Patent Grant
8816272
This disclosure relates to identification of substances using mass spectrometry.
Mass spectrometers are widely used for the detection of chemical substances. In a typical mass spectrometer, molecules or particles are excited or ionized, and these excited species often break down to form ions of smaller mass or react with other species to form other characteristic ions. The ion formation pattern can be interpreted by a system operator to infer the identity of the compound.
In general, in a first aspect, the disclosure features mass spectrometers that include an ion source, an ion trap, an ion detector, and a gas pressure regulation system, where during operation of the mass spectrometers, the gas pressure regulation system is configured to maintain a gas pressure of between 100 mTorr and 100 Torr in at least two of the ion source, the ion trap, and the ion detector, and the ion detector is configured to detect ions generated by the ion source according to a mass-to-charge ratio of the ions.
Embodiments of the mass spectrometers can include any one or more of the following features.
During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr in the ion trap and the ion detector. During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr in the ion source and the ion trap. During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr in the ion source and the ion detector. During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr in the ion source, the ion trap, and the ion detector.
The ion source can include a glow discharge ionization source. The ion source can include a capacitive discharge ionization source. The ion source can include a dielectric barrier discharge ionization source.
The gas pressure regulation system can include a gas pump configured to control the gas pressure in the at least two of the ion source, the ion trap, and the ion detector. The mass spectrometers can include a controller configured to activate the gas pump to control the gas pressure in the at least two of the ion source, the ion trap, and the ion detector. The gas pump can include a scroll pump.
During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 500 mTorr and 10 Torr in the at least two of the ion source, the ion trap, and the ion detector. During operation, the gas pressure regulation system can be configured to maintain gas pressures in at least two of the ion source, the ion trap, and the ion detector that differ by an amount less than 10 Torr. During operation, the gas pressure regulation system can be configured to maintain gas pressures in the ion source, the ion trap, and the ion detector that differ by an amount less than 10 Torr. During operation, the gas pressure regulation system can be configured to maintain the same gas pressure in at least two of the ion source, the ion trap, and the ion detector. During operation, the gas pressure regulation system can be configured to maintain the same gas pressure in the ion source, the ion trap, and the ion detector.
The mass spectrometers can include: a gas path, where the ion source, the ion trap, and the ion detector are connected to the gas path; and a gas inlet connected to the gas path and configured so that, during operation, gas particles to be analyzed are introduced into the gas path through the gas inlet, and a pressure of the gas particles to be analyzed in the gas path is between 100 mTorr and 100 Torr. The gas inlet can be configured so that during operation, a mixture of gas particles including the gas particles to be analyzed and atmospheric gas particles are drawn into the gas inlet, and the mixture of gas particles is not filtered to remove atmospheric gas particles before being introduced into the gas path.
The mass spectrometers can include a sample gas inlet connected to the gas path, and a buffer gas inlet connected to the gas path, where the sample gas inlet and the buffer gas inlet are configured so that during operation of the mass spectrometer: gas particles to be analyzed are introduced into the gas path through the sample gas inlet; buffer gas particles are introduced into the gas path through the buffer gas inlet; and a combined pressure of the gas particles to be analyzed and the buffer gas particles in the gas path is between 100 mTorr and 100 Torr. The buffer gas particles can include nitrogen molecules and/or noble gas molecules.
The ion source and the ion trap can be enclosed within a housing that includes a first plurality of electrodes, and the mass spectrometers can further include a support base featuring a second plurality of electrodes configured to releasably engage the first plurality of electrodes so that the housing can be repeatedly connected to and disconnected from the support base. The mass spectrometers can include an attachment mechanism configured to secure the housing to the support base when the first plurality of electrodes is engaged with the second plurality of electrodes. The attachment mechanism can include at least one of a clamp and a cam.
The first plurality of electrodes can include pins, and the second plurality of electrodes can include sockets configured to receive the pins.
The ion detector can be enclosed within the housing. The gas pressure regulation system can include a pump, and the pump can be enclosed within the housing.
The support base can include a voltage source coupled to the second plurality of electrical contacts, and a controller connected to the voltage source, where the controller is further connected to the ion source and the ion trap when the housing is connected to the support base. During operation, the controller can be configured to determine the gas pressure in the at least one of the ion source, the ion trap, and the ion detector, and control the gas pressure by activating the gas pressure regulation system.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features methods that include maintaining a gas pressure of between 100 mTorr and 100 Torr in at least two of an ion source, an ion trap, and an ion detector of a mass spectrometers, and detecting ions generated by the ion source according to a mass-to-charge ratio of the ions.
Embodiments of the methods can include any one or more of the following features.
The methods can include maintaining a gas pressure of between 100 mTorr and 100 Torr in the ion trap and the ion detector. The methods can include maintaining a gas pressure of between 100 mTorr and 100 Torr in the ion source and the ion trap. The methods can include maintaining a gas pressure of between 100 mTorr and 100 Torr in the ion source and the ion detector. The methods can include maintaining a gas pressure of between 100 mTorr and 100 Torr in the ion source, the ion trap, and the ion detector. The methods can include maintaining a gas pressure of between 500 mTorr and 10 Torr in the at least two of the ion source, the ion trap, and the ion detector. The methods can include maintaining gas pressures in at least two of the ion source, the ion trap, and the ion detector that differ by an amount less than 10 Torr. The methods can include maintaining gas pressures in the ion source, the ion trap, and the ion detector that differ by an amount less than 10 Torr. The methods can include maintaining the same gas pressure in at least two of the ion source, the ion trap, and the ion detector. The methods can include maintaining the same gas pressure in the ion source, the ion trap, and the ion detector.
The methods can include introducing gas particles to be analyzed into a gas path connecting the ion source, the ion trap, and the ion detector through a gas inlet, so that a pressure of the gas particles to be analyzed in the gas path is between 100 mTorr and 100 Torr. The methods can include introducing a mixture of gas particles into a gas path connecting the ion source, the ion trap, and the ion detector through a gas inlet, where the mixture of gas particles includes gas particles to be analyzed and atmospheric gas particles, and the mixture of gas particles is not filtered to remove atmospheric gas particles before being introduced into the gas path.
The methods can include introducing gas particles to be analyzed into a gas path connecting the ion source, the ion trap, and the ion detector through a sample gas inlet, and introducing buffer gas particles into the gas path through a buffer gas inlet, where a combined pressure of the gas particles to be analyzed and the buffer gas particles in the gas path is between 100 mTorr and 100 Torr. The buffer gas particles can include nitrogen molecules and/or noble gas molecules.
Embodiments of the methods can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features mass spectrometers that include a support base featuring a first plurality of electrodes, and a pluggable module featuring a second plurality of electrodes, where the pluggable module is configured to releasably connect to the support base by engaging the second plurality of electrical connectors with the first plurality of electrical connectors, and where the pluggable module includes an ion trap connected to a gas path.
Embodiments of the mass spectrometers can include any one or more of the following features.
The pluggable module can include an ion trap connected to the gas path. The second plurality of electrodes can include pins, and the first plurality of electrodes can include sockets configured to receive the pins.
The support base comprises a first attachment mechanism and the pluggable module comprises a second attachment mechanism configured to engage with the first attachment mechanism.
The first and second attachment mechanisms can be configured so that the pluggable module releasably connects to the support base in only one orientation. One of the first and second attachment mechanisms can include an asymmetric extended member, and the other one of the first and second attachment mechanisms can include a recess configured to receive the extended member. At least one of the first and second attachment mechanisms can include a flexible sealing member. At least one of the first and second attachment mechanisms can include at least one of a clamp and a cam.
The mass spectrometers can include a gas inlet connected to the gas path. The mass spectrometers can include an ion detector attached to the support base. The pluggable module can include an ion detector connected to the gas path. The ion detector can be positioned on the support base so that when the pluggable module is connected to the support base, the ion detector is connected to the gas path.
The mass spectrometers can include a pump attached to the support base. The pluggable module can include a pump connected to the gas path. The pump can be positioned on the support base so that when the pluggable module is connected to the support base, the pump is connected to the gas path. The pump can include a scroll pump.
The ion source can include a glow discharge ionization source and/or capacitive discharge ionization source.
The mass spectrometers can include an ion detector connected to the gas path, and a controller attached to the support base and connected to the ion trap. During operation of the mass spectrometers, the controller can be configured to detect ions generated by the ion source using the detector, determine information related to an identity of the detected ions, and display the information using an output interface.
The mass spectrometers can include a pump connected to the gas path and configured to maintain the pressure of the gas particles in a range from 100 mTorr to 100 Torr. The mass spectrometers can include a controller connected to the ion trap and the pump, where during operation of the mass spectrometers, the controller can be configured to determine a pressure of gas particles in the gas path, and activate the pump to maintain the pressure of the gas particles in a range from 100 mTorr to 100 Torr.
The pump can be configured to maintain the pressure of the gas particles in a range from 100 mTorr to 100 Torr.
The mass spectrometers an include an enclosure surrounding the support base and the pluggable module, where the enclosure includes an opening positioned adjacent to the pluggable module to allow a user of the mass spectrometers to connect and disconnect the pluggable module from the support base through the opening. The mass spectrometers can include a covering member that, when deployed, seals the opening in the enclosure. The covering member can include a retractable door. The covering member can include a lid that fully detaches from the enclosure.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features mass spectrometer systems that include any of the mass spectrometers disclosed herein that feature a first pluggable module, and one or more additional pluggable modules, where each of the additional pluggable modules includes an ion trap and a third plurality of electrodes, and each of the additional pluggable modules is configured to releasably connect to the support base by engaging the third plurality of electrodes with the first plurality of electrodes.
Embodiments of the systems can include any one or more of the following features.
At least one of the additional pluggable modules can include an ion trap that is substantially similar to the ion trap of the first pluggable module.
The first pluggable module can include an ion source, and at least one of the additional pluggable modules can include an ion source that differs from the ion source of the first pluggable module. For example, the ion source of the first pluggable module can include a glow discharge ionization source, and at least one of the additional pluggable modules can include an ionization source that is different from a glow discharge ionization source (e.g., an electrospray ionization source, a dielectric barrier discharge ionization source, and/or a capacitive discharge ionization source).
At least one of the additional pluggable modules can include an ion trap that differs from the ion trap of the first pluggable module. A diameter of the ion trap of the first pluggable module can differ from a diameter of an ion trap of at least one of the additional pluggable modules. Alternatively, or in addition, a cross-sectional shape of the ion trap of the first pluggable module can differ from a cross-sectional shape of an ion trap of at least one of the additional pluggable modules.
The first pluggable module can include an ion detector and each of the additional pluggable modules can include an ion detector, and the ion detector of the first pluggable module can differ from the ion detector of at least one of the additional pluggable modules.
At least one surface of the first pluggable module can include a first coating, and at least one surface of at least one of the additional pluggable modules can include a second coating different from the first coating.
Embodiments of the systems can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features mass spectrometers that include a support base, an ion source mounted to the support base, an ion trap mounted to the support base, an ion detector mounted to the support base, and an electrical power source mounted to the support base and electrically connected through the support base to the ion source, the ion trap, and the ion detector, where during operation of the mass spectrometers, the electrical power source is configured to provide electrical power to the ion source, the ion trap, and the ion detector.
Embodiments of the mass spectrometers can include any one or more of the following features.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
The mass spectrometers can include a gas pressure regulation system mounted to the support base and electrically connected through the support base to the electrical power source, where during operation of the mass spectrometers, the electrical power source is configured to provide electrical power to the gas pressure regulation system. The mass spectrometers can include a controller mounted to the support base and electrically connected through the support base to the ion source, the ion trap, the ion detector, and the gas pressure regulation system. The ion source, the ion trap, and the ion detector can be connected to a gas path, and during operation of the mass spectrometers, the gas pressure regulation system can be configured maintain a gas pressure in the gas path in a range from 100 mTorr to 100 Torr (e.g., in a range from 500 mTorr to 10 Torr). The gas pressure regulation system can include a scroll pump.
The support base can include a printed circuit board.
The mass spectrometers can include a gas inlet connected to the gas path, where the gas inlet is configured so that during operation of the mass spectrometers, a mixture of gas particles are introduced into the gas path through the gas inlet, the mixture including gas particles to be analyzed and atmospheric gas particles, and the mixture of gas particles is introduced into the gas path without filtering the atmospheric gas particles. The gas inlet can include a valve that is electrically connected to the controller, and during operation of the mass spectrometers, the controller can be configured to introduce the mixture of gas particles into the gas path through the gas inlet during an interval of at least 30 seconds.
During operation of the mass spectrometers, the controller can be configured to use the ion detector to detect ions generated by the ion source, and adjust a duty cycle of the ion source based on the detected ions. The controller can be configured to adjust the duty cycle of the ion source by adjusting a time interval during which the ion source generates ions. The controller can be configured to adjust the duty cycle of the ion source by adjusting at least one of a duration and a magnitude of an electrical potential applied to an electrode of the ion source.
During operation of the mass spectrometers, the controller can be configured to determine information related to an identity of the detected ions, and display the information using an output interface.
The ion source can include a glow discharge ionization source and/or a dielectric barrier discharge ionization source.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features mass spectrometers that include: an ion source, an ion trap, and a detector connected to a gas path; a gas inlet connected to the gas path and featuring a valve; a pressure regulation system configured to control gas pressure in the gas path; and a controller connected to the valve, the ion source, the ion trap, and the detector, where during operation of the mass spectrometers, the pressure regulation system is configured to maintain a gas pressure in the gas path of greater than 100 mTorr, and the controller is configured to: (a) activate the valve to introduce a mixture of gas particles into the gas path, where the mixture comprises gas particles to be analyzed and atmospheric gas particles, and where the mixture of gas particles is introduced without filtering the atmospheric gas particles; (b) activate the ion source to generate ions from the gas particles to be analyzed; and (c) activate the detector to detect the ions according to a mass-to-charge ratio for the ions.
Embodiments of the mass spectrometers can include any one or more of the following features.
The atmospheric gas particles can include at least one of molecules of nitrogen and molecules of oxygen. The pressure regulation system can configured to maintain a gas pressure in the gas path of greater than 500 mTorr (e.g., greater than 1 Torr). The controller can be configured to activate the valve to continuously introduce the mixture of gas particles into the gas path over a period of at least 10 seconds (e.g., over a period of at least 30 seconds, over a period of at least 1 minute, over a period of at least 2 minutes).
The mass spectrometers can include: a housing enclosing the ion source and the ion trap, and featuring a first plurality of electrodes connected to the ion source and the ion trap; and a support base featuring a second plurality of electrodes configured to engage the first plurality of electrodes, where the housing forms a pluggable module configured to releasably connect to the support base. The controller can be connected to the support base.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
During operation, the controller can be configured to adjust a duty cycle of the ion source based on the detected ions. For example, the controller can be configured to adjust the ion source so that ions are produced from the gas particles to be analyzed for a continuous period of 10 seconds or more (e.g., for a continuous period of 30 seconds or more, for a continuous period of 1 minute or more, for a continuous period of 2 minutes or more).
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features methods that include: introducing a mixture of gas particles into a gas path of a mass spectrometer, where the mixture includes gas particles to be analyzed and atmospheric gas particles, and where the mixture of gas particles is introduced without filtering the atmospheric gas particles; maintaining a gas pressure in the gas path of greater than 100 mTorr; generating ions from the gas particles to be analyzed using an ion source connected to the gas path; and detecting the ions according to a mass-to-charge ratio for the ions using a detector connected to the gas path.
Embodiments of the methods can include any one or more of the following features.
The atmospheric gas particles can include at least one of molecules of nitrogen and molecules of oxygen.
The methods can include maintaining a gas pressure in the gas path of greater than 500 mTorr (e.g., greater than 1 Torr). The methods can include continuously introducing the mixture of gas particles into the gas path over a period of at least 10 seconds (e.g., over a period of at least 30 seconds, over a period of at least 2 minutes). The methods can include adjusting the ion source so that ions are produced from the gas particles to be analyzed for a continuous period of 10 seconds or more (e.g., for a continuous period of 30 seconds or more, for a continuous period of 2 minutes or more).
Embodiments of the methods can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features mass spectrometers that include an ion source, an ion trap, an ion detector, a pressure regulation system featuring a single mechanical pump configured to control gas pressure in the ion source, ion trap, and ion detector, and a controller connected to the ion source, the ion trap, and the ion detector, where the single mechanical pump operates at a frequency of less than 6000 cycles per minute to control the gas pressure, and where during operation of the mass spectrometers, the controller is configured to activate the ion detector to detect ions generated by the ion source according to a mass-to-charge ratio of the ions.
Embodiments of the mass spectrometers can include any one or more of the following features.
The single mechanical pump can include a scroll pump. The single mechanical pump can operate at a frequency of less than 4000 cycles per minute to control the gas pressure.
During operation of the mass spectrometers, the single mechanical pump can maintain a gas pressure of between 100 mTorr and 100 Torr in at least two of the ion source, the ion trap, and the ion detector. During operation of the mass spectrometers, the single mechanical pump can maintain a gas pressure of between 500 mTorr and 10 Torr in at least two of the ion source, the ion trap, and the ion detector. During operation of the mass spectrometers, the single mechanical pump can maintain a common gas pressure in at least two of the ion source, the ion trap, and the ion detector. During operation of the mass spectrometers, the single mechanical pump can maintain gas pressures in the ion source, the ion trap, and the ion detector that differ by 10 mTorr or less.
The controller can be connected to the pump, and during operation of the mass spectrometers, the controller can be configured to control the frequency of the pump. During operation of the mass spectrometers, the controller is configured to detect ions generated by the ion source using the ion detector, and adjust the frequency of the pump based on the detected ions.
The ion source can include a glow discharge ionization source, a dielectric barrier discharge ionization source, and/or a capacitive discharge ionization source.
The mass spectrometers can include a housing enclosing the ion source and the ion trap, and featuring a first plurality of electrodes connected to the ion source and the ion trap, and a support base featuring a second plurality of electrodes configured to engage the first plurality of electrodes, where the housing is a pluggable module configured to releasably connect to the support base. The housing can enclose the pump. The controller can be mounted on the support base. The support base can include a printed circuit board. The electronic processor can be electrically connected to the ion source and the ion trap through the support base.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers is less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features methods that include using a single mechanical pump to control gas pressure in an ion source, an ion trap, and an ion detector of a mass spectrometer, and using the ion detector to detect ions generated by the ion source according to a mass-to-charge ratio of the ions, where using the single mechanical pump to control gas pressure includes operating the pump at a frequency of less than 6000 cycles per minute to control the gas pressure.
Embodiments of the methods can include any one or more of the following features.
The methods can include operating the pump at a frequency of less than 4000 cycles per minute to control the gas pressure. The methods can include maintaining a gas pressure of between 100 mTorr and 100 Torr (e.g., between 500 mTorr and 10 Torr) in at least two of the ion source, the ion trap, and the ion detector.
The methods can include maintaining a common gas pressure in at least two of the ion source, the ion trap, and the ion detector. The methods can include maintaining gas pressures in the ion source, the ion trap, and the ion detector that differ by 10 mTorr or less.
The methods can include adjusting the frequency of the pump based on the detected ions (e.g., based on abundances of the detected ions).
Embodiments of the methods can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features mass spectrometers that include an ion source, an ion trap, an ion detector, a user interface, and a controller connected to the ion source, the ion trap, the ion detector, and the user interface, where during operation of the mass spectrometers, the controller is configured to, detect ions generated by the ion source using the ion detector, determine a chemical name associated with the detected ions, and display the chemical name on the user interface, and where the user interface includes a control that, when activated by a user after the display of the chemical name, causes the controller to display a spectrum of the detected ions on the user interface.
Embodiments of the mass spectrometers can include any one or more of the following features.
Displaying the spectrum of the detected ions includes displaying abundances of the detected ions as a function of a mass-to-charge ratio of the ions. The control can include at least one of a button, a switch, and a region of a touchscreen display. During operation of the mass spectrometers, the controller can be further configured to display hazards associated with the detected ions on the user interface.
The ion source can be at least one of a glow discharge ionization source, a capacitive discharge ionization source, and a dielectric barrier discharge ionization source.
During operation of the mass spectrometers, the controller can be configured so that the spectrum of the detected ions is not displayed unless the control is activated.
The ion detector can include a Faraday detector.
The mass spectrometers can include a pressure regulation system, where during operation of the mass spectrometers, the pressure regulation system is configured to maintain a gas pressure of between 100 mTorr and 100 Torr (e.g., between 500 mTorr and 10 Torr) in the ion trap and the ion detector.
The pressure regulation system can include a scroll pump.
The mass spectrometers can include a pluggable module featuring the ion source, the ion trap, and a first plurality of electrodes connected to the ion source and the ion trap, and a support base featuring a voltage source and a second plurality of electrodes configured to engage the first plurality of electrodes, where the pluggable module is configured to releasably connect to the support base.
The pluggable module can include the ion detector. The pluggable module can include a pressure regulation system.
The mass spectrometers can include a housing enclosing the pluggable module and the support base, and featuring an opening positioned adjacent to the pluggable module and configured to allow the pluggable module to be inserted through the opening to releasably connect to the support base.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features mass spectrometers that include an ion source, an ion trap, an ion detector, a user interface, and a controller connected to the ion source, the ion trap, the ion detector, and the user interface, where the user interface includes a control that can be activated to one of at least two states by a user of the mass spectrometer, and where during operation of the mass spectrometer, the controller is configured to detect ions generated by the ion source using the ion detector, determine a chemical name associated with the detected ions, and: if the control is activated to a first state, display the chemical name on the user interface; and if the control is activated to a second state, display a spectrum of the detected ions on the user interface.
Embodiments of the mass spectrometers can include any one or more of the following features.
If the control is activated to the second state, the controller can be further configured to display the chemical name on the user interface. Displaying the spectrum of the detected ions can include displaying abundances of the detected ions as a function of a mass-to-charge ratio of the ions. The control can include at least one of a button, a switch, and a region of a touchscreen display.
The ion source can be at least one of a glow discharge ionization source, a capacitive discharge ionization source, and/or a dielectric barrier discharge ionization source.
The mass spectrometers can include a pressure regulation system connected to the controller, where during operation of the mass spectrometers, the pressure regulation system is configured to maintain a gas pressure of between 100 mTorr and 100 Torr (e.g., between 500 mTorr and 10 Torr) in the ion trap and the ion detector. The pressure regulation system can include a scroll pump.
The mass spectrometers can include: a pluggable module that includes the ion source, the ion trap, and a first plurality of electrodes connected to the ion source and the ion trap; and a support base that includes a voltage source and a second plurality of electrodes configured to engage the first plurality of electrodes, where the pluggable module is configured to releasably connect to the support base. The pluggable module can include the ion detector and/or a pressure regulation system.
The mass spectrometers can include a housing enclosing the pluggable module and the support base, and featuring an opening positioned adjacent to the pluggable module and configured to allow the pluggable module to be inserted through the opening to releasably connect to the support base.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features mass spectrometers that include an ion source, an ion trap, an ion detector, a sample inlet, and a pressure regulation system, where the ion source, the ion trap, the ion detector, the sample inlet, and the pressure regulation system are connected to a gas path, and where during operation of the mass spectrometers, gas particles are introduced into the gas path only through the sample inlet, the pressure regulation system is configured to maintain a gas pressure in the gas path of between 100 mTorr and 100 Torr, and the ion detector is configured to detect ions generated by the ion source from the gas particles according to a mass-to-charge ratio of the ions.
Embodiments of the mass spectrometers can include any one or more of the following features.
The pressure regulation system can be configured to maintain the gas pressure between 500 mTorr and 10 Torr. The pressure regulation system can be configured to maintain the gas pressure above 500 mTorr.
The ion source can include at least one of a glow discharge ionization source, a capacitive discharge ionization source, and a dielectric barrier discharge ionization source.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
The pressure regulation system can include a scroll pump.
The sample inlet can be configured so that the gas particles that are introduced into the gas path include gas particles to be analyzed and atmospheric gas particles.
The mass spectrometers can include a valve connected to the sample inlet and a controller connected to the valve, where during operation of the mass spectrometers, the controller can be configured to continuously introduce the gas particles into the gas path through the sample inlet for a period of at least 30 seconds (e.g., for a period of at least 1 minute, for a period of at least 2 minutes).
The mass spectrometers can include a controller connected to the ion source, where during operation of the mass spectrometers, the controller can be configured to adjust an electrical potential applied to the ion source so that ions are continuously produced from the gas particles by the ion source for a period of at least 30 seconds (e.g., for a period of at least 1 minute, for a period of at least 2 minutes).
The mass spectrometers can include a pluggable module featuring the ion source, the ion trap, and a first plurality of electrodes connected to the ion source and the ion trap, and a support base featuring a voltage source and a second plurality of electrodes configured to engage the first plurality of electrodes, where the pluggable module is configured to releasably connect to the support base. The pluggable module can include the pressure regulation system.
The mass spectrometers can include a housing enclosing the pluggable module and the support base, and featuring an opening positioned adjacent to the pluggable module and configured to allow the pluggable module to be inserted through the opening to releasably connect to the support base.
The pressure regulation system can include a single mechanical pump, where during operation of the mass spectrometers, the single mechanical pump is configured to operate at a frequency of 6000 cycles per minute or less to maintain the gas pressure in the gas path.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features methods that include introducing a mixture of gas particles into a gas path of a mass spectrometer through a single gas inlet, where the mixture of gas particles includes only gas particles to be analyzed and atmospheric gas particles, maintaining a gas pressure in the gas path of between 100 mTorr and 100 Torr, and detecting ions generated from the gas particles to be analyzed according to a mass-to-charge ratio of the ions.
Embodiments of the methods can include any one or more of the following features.
The methods can include maintaining the gas pressure between 500 mTorr and 10 Torr. The methods can include maintaining the gas pressure above 500 mTorr.
The methods can include continuously introducing the mixture of gas particles into the gas path through the single gas inlet for a period of at least 30 seconds (e.g., for a period of at least 1 minute, for a period of at least 2 minutes).
The methods can include adjusting an electrical potential applied to an ion source of the mass spectrometer so that ions are continuously generated from the gas particles to be analyzed for a period of at least 30 seconds (e.g., for a period of at least 1 minute, for a period of at least 2 minutes).
The methods can include operating a single mechanical pump at a frequency of 6000 cycles per minute or less to maintain the gas pressure in the gas path.
Embodiments of the methods can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features mass spectrometers that include an ion source featuring an exit electrode through which ions leave the ion source, an ion trap featuring an entry electrode positioned adjacent to the exit electrode, an ion detector, and a pressure regulation system, where: the exit electrode includes one or more apertures defining a cross-sectional shape of the exit electrode, and the entry electrode includes one or more apertures defining a cross-sectional shape of the entry electrode; the cross-sectional shape of the exit electrode substantially matches the cross-sectional shape of the entry electrode; and during operation of the mass spectrometers, the pressure regulation system is configured to maintain a gas pressure of at least 100 mTorr in the ion trap, and the ion detector is configured to detect ions generated by the ion source according to a mass-to-charge ratio of the ions.
Embodiments of the mass spectrometers can include any one or more of the following features.
The ion trap can include one or more ion chambers, the one or more ion chambers defining a cross-sectional shape of the ion trap, and the cross-sectional shape of the ion trap can substantially match the cross-sectional shape of the entry electrode.
The one or more apertures of the exit electrode can include multiple apertures arranged in a rectangular or square array. The one or more apertures of the exit electrode can include multiple apertures arranged in a hexagonal array. The one or more apertures of the exit electrode can include an aperture having a rectangular cross-sectional shape. The one or more apertures of the exit electrode can include an aperture having a spiral cross-sectional shape. The one or more apertures of the exit electrode can include an aperture having a serpentine cross-sectional shape. The one or more apertures of the exit electrode can include 4 or more apertures (e.g., 8 or more apertures, 24 or more apertures, 100 or more apertures). The one or more apertures of the exit electrode can include a plurality of apertures arranged in a serpentine pattern.
The mass spectrometers can include a voltage source connected to the exit electrode and to a first electrode of the ion source, and a controller connected to the voltage source, where during operation of the mass spectrometers, the controller can be configured to operate the ion source in one of at least two modes by applying different electrical potentials to the first electrode and the exit electrode, the different electrical potentials being referenced to a common ground potential. In a first one of the at least two modes, the controller can be configured to apply electrical potentials to the first electrode and to the exit electrode so that the first electrode is at a positive electrical potential relative to the common ground potential, and in a second one of the at least two modes, the controller can be configured to apply electrical potentials to the first and second electrodes so that the first electrode is at a negative electrical potential relative to the common ground.
The mass spectrometers can include a user interface featuring a selectable control configured so that when the control is activated during operation of the mass spectrometer, the controller changes the operating mode of the ion source.
The ion source can include a glow discharge ionization source.
The mass spectrometers can include a detector connected to the controller, where during operation of the mass spectrometer, the controller can be configured to detect ions generated by the ion source using the ion detector, and adjust the electrical potentials applied to the first electrode and the exit electrode based on the detected ions to control a duration of time during which the ion source continuously generates ions. During operation of the mass spectrometers, the ion source can generate ions in a plurality of ionization cycles that define an ion source frequency, each ionization cycle can include a first interval during which ions are generated, and a second interval during which ions are not generated, the first and second intervals defining a duty cycle, and the controller can be configured to adjust the duty cycle to a value between 1% and 40% (e.g., to a value between 1% and 20%, to a value between 1% and 10%).
During operation of the mass spectrometers, the controller can be configured to determine when the ion source should be cleaned based on the detected ions, adjust the duty cycle of the ion source to a value between 50% and 90%, and operate the ion source for a period of at least 30 seconds to clean the ion source.
The pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr (e.g., between 500 mTorr and 10 Torr) in the ion trap.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features mass spectrometers that include an ion source, an ion trap, an ion detector, a pressure regulation system, a voltage source connected to the ion source, the ion trap, the ion detector, and the pressure regulation system, and a controller connected to the ion source, the ion trap, the ion detector, and the voltage source, where during operation of the mass spectrometers, the controller is configured to activate the ion source to generate ions from gas particles, activate the ion detector to detect ions generated by the ion source, and adjust a resolution of the mass spectrometers based on the detected ions.
Embodiments of the mass spectrometers can include any one or more of the following features.
The controller can be connected to the pressure regulation system and configured to adjust the resolution by activating the pressure regulation system to change a gas pressure in at least one of the ion source and the ion trap. The controller can be configured to increase the resolution by activating the pressure regulation system to reduce the gas pressure in the at least one of the ion source and the ion trap.
The controller can be configured to repeatedly apply an electrical potential using the voltage source to a central electrode of the ion trap to eject ions from the trap, the repeated applications of the electrical potential defining a repetition frequency of the electrical potential, and adjust the resolution by changing the repetition frequency of the electrical potential. The controller can be configured to increase the resolution by increasing the repetition frequency of the electrical potential.
The controller can be configured to adjust the resolution by changing a maximum amplitude of an electrical potential applied to a central electrode of the ion trap by the voltage source.
The controller can be configured to apply an axial electrical potential difference between electrodes at opposite ends of the ion trap using the voltage source, and adjust the resolution by changing a magnitude of the axial electrical potential difference. The controller can be configured to increase the resolution by increasing a magnitude of the axial electrical potential difference.
The controller can be configured to repeatedly apply an electrical potential difference between electrodes of the ion source using the voltage source to generate the ions, the repeated applications of the electrical potential defining a repetition frequency of the ion source, and adjust the resolution by changing the repetition frequency of the ion source. The controller can be configured to synchronize the repetition frequency of the ion source and the repetition frequency of the electrical potential applied to the central electrode of the ion trap.
The controller can be configured to: repeatedly apply an electrical potential difference between electrodes of the ion source using the voltage source, where the repeated applications of the electrical potential define a repetition period of the ion source and the repetition period includes a first time interval during which the electrical potential difference is applied between the electrodes of the ion source, and a second time interval during which the electrical potential difference is not applied between the electrodes of the ion source; and adjust the resolution by adjusting a duty cycle of the ion source, where the duty cycle corresponds to a ratio of the first time interval to the repetition period. The controller can be configured to increase the resolution by decreasing the duty cycle of the ion source.
The mass spectrometers can include a gas path, where the ion source, the ion trap, the ion detector, and the pressure regulation system are connected to the gas path, and a buffer gas inlet connected to the gas path, and featuring a valve connected to the controller, where the controller is configured to control the valve to adjust a rate at which buffer gas particles are introduced into the gas path through the buffer gas inlet to adjust the resolution. The controller can be configured to increase the rate at which buffer gas particles are introduced into the gas path to increase the resolution.
During operation of the mass spectrometers, the controller can be configured to: repeatedly activate the ion source to generate ions from gas particles, activate the ion detector to detect ions generated by the ion source, and adjust the resolution of the mass spectrometer based on the detected ions, until the resolution of the mass spectrometer reaches a threshold value; activate the ion detector to detect ions generated from the gas particles when the resolution of the mass spectrometer is at least as large as the threshold value; determine information about an identity of the gas particles based on ions detected when the resolution of the mass spectrometer is at least as large as the threshold value; and display the information on a user interface. The information can include a chemical name of the gas particles and/or information about hazards associated with the gas particles and/or information about a class of substances to which the gas particles correspond.
During operation of the mass spectrometers, the controller can be configured to adjust the voltage source so that an electrical potential is applied to a central electrode of the ion trap only when the resolution reaches the threshold value.
During operation of the mass spectrometers, the pressure regulation system can be configured to maintain a gas pressure in at least two of the ion source, the ion trap, and the ion detector of between 100 mTorr and 100 Torr (e.g., between 500 mTorr and 10 Torr).
The mass spectrometers can include a pluggable module featuring the ion source, the ion trap, the detector, and a first plurality of electrodes connected to the ion source, the ion trap, and the detector, and a support base featuring a second plurality of electrodes configured to engage the first plurality of electrodes, where the voltage source and the controller are mounted on the support base, and where the pluggable module is configured to releasably connect to the support base.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features methods that include introducing gas particles into an ion source of a mass spectrometer, generating ions from the gas particles, detecting the ions using a detector of the mass spectrometer, and adjusting a resolution of the mass spectrometer based on the detected ions.
Embodiments of the methods can include any one or more of the following features.
Adjusting the resolution can include changing a gas pressure in at least one of the ion source and the ion trap. The methods can include increasing the resolution by reducing the gas pressure in the at least one of the ion source and the ion trap.
The methods can include repeatedly applying an electrical potential to a central electrode of the ion trap to eject ions from the trap, the repeated applications of the electrical potential defining a repetition frequency of the electrical potential, and adjusting the resolution by changing the repetition frequency of the electrical potential. The methods can include increasing the resolution by increasing the repetition frequency of the electrical potential. The methods can include adjusting the resolution by changing a maximum amplitude of an electrical potential applied to a central electrode of the ion trap.
The methods can include applying an axial electrical potential difference between electrodes at opposite ends of the ion trap, and adjusting the resolution by changing a magnitude of the axial electrical potential difference. The methods can include increasing the resolution by increasing a magnitude of the axial electrical potential difference.
The methods can include repeatedly applying an electrical potential difference between electrodes of the ion source to generate the ions, the repeated applications of the electrical potential defining a repetition frequency of the ion source, and adjusting the resolution by changing the repetition frequency of the ion source. The methods can include synchronizing the repetition frequency of the ion source and the repetition frequency of the electrical potential applied to the central electrode of the ion trap.
The methods can include: repeatedly applying an electrical potential difference between electrodes of the ion source, where the repeated applications of the electrical potential define a repetition period of the ion source, and the repetition period includes a first time interval during which the electrical potential difference is applied between the electrodes of the ion source, and a second time interval during which the electrical potential difference is not applied between the electrodes of the ion source; and adjusting the resolution by adjusting a duty cycle of the ion source, where the duty cycle corresponds to a ratio of the first time interval to the repetition period. The methods can include increasing the resolution by decreasing the duty cycle of the ion source.
The methods can include adjusting a rate at which buffer gas particles are introduced into a gas path of the mass spectrometer to adjust the resolution. The methods can include increasing the rate at which buffer gas particles are introduced into the gas path to increase the resolution.
The methods can include: repeatedly activating the ion source to generate ions from gas particles, activating the ion detector to detect ions generated by the ion source, and adjusting the resolution of the mass spectrometer based on the detected ions, until the resolution of the mass spectrometer reaches a threshold value; activating the ion detector to detect ions generated from the gas particles when the resolution of the mass spectrometer is at least as large as the threshold value; determining information about an identity of the gas particles based on ions detected when the resolution of the mass spectrometer is at least as large as the threshold value; and displaying the information on a user interface. The information can include a chemical name of the gas particles and/or information about hazards associated with the gas particles and/or information about a class of substances to which the gas particles correspond.
The methods can include applying an electrical potential to a central electrode of the ion trap only when the resolution reaches the threshold value.
The methods can include maintaining a gas pressure in at least two of the ion source, the ion trap, and the ion detector of between 100 mTorr and 100 Torr (e.g., between 500 mTorr and 10 Torr).
Embodiments of the methods can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features mass spectrometers that include an ion source, an ion trap, an ion detector, a gas pressure regulation system featuring a single mechanical pump, and a controller connected to the ion source, the ion trap, and the ion detector, where during operation of the mass spectrometers, the gas pressure regulation system is configured to maintain a gas pressure of between 100 mTorr and 100 Torr in at least two of the ion source, the ion trap, and the ion detector, and the controller is configured to activate the ion detector to detect ions generated by the ion source according to a mass-to-charge ratio of the ions, and where the single mechanical pump operates at a frequency of less than 6000 cycles per minute to maintain the gas pressure.
Embodiments of the mass spectrometers can include one or more of the following features. During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr in the ion trap and the ion detector. During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr in the ion source and the ion trap. During operation, the gas pressure regulation system can be configured to maintain a gas pressure of between 100 mTorr and 100 Torr in the ion source, the ion trap, and the ion detector.
The mechanical pump can be a scroll pump.
During operation, the gas pressure regulation system can be configured to maintain gas pressures in at least two of the ion source, the ion trap, and the ion detector that differ by an amount less than 10 Torr. During operation, the gas pressure regulation system can be configured to maintain gas pressures in the ion source, the ion trap, and the ion detector that differ by an amount less than 10 Torr. During operation, the gas pressure regulation system can be configured to maintain the same gas pressure in at least two of the ion source, the ion trap, and the ion detector.
The mass spectrometers can include a gas path, where the ion source, the ion trap, the ion detector, and the gas pressure regulation system are connected to the gas path, and a gas inlet connected to the gas path and configured so that, during operation of the mass spectrometers, gas particles to be analyzed are introduced into the gas path through the gas inlet, and a total gas pressure in the gas path is between 100 mTorr and 100 Torr. The gas inlet can be configured so that during operation of the mass spectrometers, a mixture of gas particles including the gas particles to be analyzed and atmospheric gas particles are drawn into the gas inlet, where the mixture of gas particles is not filtered to remove atmospheric gas particles before being introduced into the gas path.
The mass spectrometers can include a gas path, where the ion source, the ion trap, the ion detector, and the gas pressure regulation system are connected to the gas path, a sample gas inlet connected to the gas path, and a buffer gas inlet connected to the gas path, where the sample gas inlet and the buffer gas inlet are configured so that during operation of the mass spectrometer, gas particles to be analyzed are introduced into the gas path through the sample gas inlet, buffer gas particles are introduced into the gas path through the buffer gas inlet, and a combined pressure of the gas particles to be analyzed and the buffer gas particles in the gas path is between 100 mTorr and 100 Torr. The buffer gas particles can include at least one of nitrogen molecules and noble gas molecules.
The mass spectrometers can include a pluggable module featuring the ion source, the ion trap, and a first plurality of electrodes connected to the ion source and the ion trap, and a support base featuring a second plurality of electrodes configured to releasably engage the first plurality of electrodes, so that the pluggable module can be connected to and disconnected from the support base. The mass spectrometers can include an attachment mechanism configured to secure the pluggable module to the support base when the first plurality of electrodes is engaged with the second plurality of electrodes. The first plurality of electrodes can include pins, and the second plurality of electrodes can include sockets configured to receive the pins.
The pluggable module can include the ion detector, and the first plurality of electrodes can be connected to the ion detector. The pluggable module can include the mechanical pump.
The mass spectrometers can include a voltage source, where the voltage source and the controller are attached to the support base and connected to the second plurality of electrodes.
The support base can include a printed circuit board. The controller can be connected to the ion source and the ion trap when the pluggable module is connected to the support base.
The single mechanical pump can operate at a frequency of less than 4000 cycles per minute to maintain the gas pressure.
A maximum dimension of the mass spectrometers can be less than 35 cm. A total mass of the mass spectrometers can be less than 4.5 kg.
Embodiments of the mass spectrometers can also include any of the other features disclosed herein, in any combination, as appropriate.
In another aspect, the disclosure features methods that include using a single mechanical pump operating at a frequency of less than 6000 cycles per minute to maintain a gas pressure in at least two of an ion source, an ion trap, and an ion detector of a mass spectrometer, and detecting ions generated by the ion source according to a mass-to-charge ratio of the ions, where the gas pressure in the at least two of the ion source, the ion trap, and the ion detector is maintained between 100 mTorr and 100 Torr.
Embodiments of the methods can include any one or more of the following features.
The gas pressure in the ion source and the ion trap can be maintained between 100 mTorr and 100 Torr. The gas pressure in the ion trap and the detector can be maintained between 100 mTorr and 100 Torr. The methods can include maintaining gas pressures in at least two of the ion source, the ion trap, and the ion detector that differ by an amount less than 10 Torr. The methods can include maintaining the same gas pressure in the ion source, the ion trap, and the ion detector.
The methods can include introducing a mixture of gas particles into a gas path connecting the ion source, the ion trap, and the ion detector, where the mixture of gas particles includes gas particles to be analyzed and atmospheric gas particles, and the mixture of gas particles is not filtered to remove atmospheric gas particles before being introduced into the gas path.
The methods can include operating the mechanical pump at a frequency of less than 4000 cycles per minute to control the gas pressure.
Embodiments of the methods can also include any of the other features disclosed herein, in any combination, as appropriate.
In a further aspect, the disclosure features mass spectrometry systems that include an ion source, an ion trap, an ion detector, and an electronic processor connected to the ion source, the ion trap, and the ion detector, and configured to operate the ion source and ion trap in at least two ionization modes during a survey time period of 500 ms or less, where in a first ionization mode of the at least two ionization modes, the electronic processor is configured to operate the ion source to generate a plurality of positively charged ions from sample molecules or particles in the system, and in a second ionization mode of the at least two ionization modes, the electronic processor is configured to operate the ion source to generate a plurality of negatively charged ions from sample molecules or particles in the system.
Embodiments of the systems can include any one or more of the following features.
In the first ionization mode, the electronic processor can be configured to operate the ion trap and the ion detector to detect positively charged ions corresponding to a first range of masses, and in the second ionization mode, the electronic processor can be configured to operate the ion trap and the ion detector to detect negatively charged ions corresponding to a second range of masses. The first and second ranges of masses can be different. Alternatively, the first and second ranges of masses can be the same.
The at least two ionization modes can include a third ionization mode, and in the third ionization mode, the electronic processor can be configured to operate the ion source to generate a plurality of positively charged ions from sample molecules or particles in the system. In the third ionization mode, the electronic processor can be configured to operate the ion trap and the ion detector to detect positively charged ions corresponding to a third range of masses. The third range of masses can be different from the first range of masses. The third range of masses can correspond to masses that are larger than masses corresponding to the first range of masses.
The at least two ionization modes can include a fourth ionization mode, and in the fourth ionization mode, the electronic processor can be configured to operate the ion source to generate a plurality of negatively charged ions from sample molecules or particles in the system. In the fourth ionization mode, the electronic processor can be configured to operate the ion trap and the ion detector to detect negatively charged ions corresponding to a fourth range of masses. The fourth range of masses can be the same as the third range of masses. Alternatively, the fourth range of masses can be different from the third range of masses. The fourth range of masses can be different from the second range of masses. The fourth range of masses can correspond to masses that are larger than masses corresponding to the second range of masses.
The electronic processor can be configured to apply a first electrical potential to a detection element of the ion detector to detect positively charged ions, and a second electrical potential different from the first electrical potential to the detection element to detect negatively charged ions. The electronic processor can be configured to apply the first electrical potential to the detection element during a first portion of the survey time period, and to apply the second electrical potential to the detection element during a second portion of the survey time period that is different from the first portion. During the first portion of the survey time period, the electronic processor can be configured to operate the ion source in the first ionization mode, and during the second portion of the survey time period, the electronic processor can be configured to operate the ion source in the second ionization mode.
The ion detector can include a plurality of detection elements. The electronic processor can be configured to apply the first electrical potential to each of the detection elements to detect positively charged ions, and the second electrical potential to each of the detection elements to detect negatively charged ions. The electronic processor can be configured to apply the first electrical potential to a first subset of the detection elements, and the second electrical potential to a second subset of the detection elements. The electronic processor can be configured to apply the first electrical potential to the first subset of the detection elements during a first portion of the survey time period, and to apply the second electrical potential to the second subset of the detection elements during a second portion of the survey time period that is different from the first portion. During the first portion of the survey time period, the electronic processor can be configured to operate the ion source in the first ionization mode, and during the second portion of the survey time period, the electronic processor can be configured to operate the ion source in the second ionization mode.
The electronic processor can be configured to apply the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during a common portion of the survey time period. The electronic processor can be configured to apply the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during the entire survey time period.
The electronic processor can be configured to apply a first electrical potential to a detection element of the ion detector to detect positively charged ions, and a second electrical potential different from the first electrical potential to the detection element to detect negatively charged ions. The electronic processor can be configured to apply the first electrical potential to the detection element during portions of the survey time period in which the ion source is operated in the first and third ionization modes. The electronic processor can be configured to apply the second electrical potential to the detection element during portions of the survey time period in which the ion source is operated in the second and fourth ionization modes.
The ion detector can include a plurality of detection elements. The electronic processor can be configured to apply a first electrical potential to each of the detection elements to detect positively charged ions, and a second electrical potential to each of the detection elements to detect negatively charged ions. The electronic processor can be configured to apply the first electrical potential to a first subset of the detection elements, and the second electrical potential to a second subset of the detection elements. The electronic processor can be configured to apply the first electrical potential to the first subset of the detection elements during portions of the survey time period in which the ion source is operated in the first and third ionization modes, and to apply the second electrical potential to the second subset of the detection elements during portions of the survey time period in which the ion source is operated in the second and fourth ionization modes. The portions of the survey time period during which the ion source is operated in the first and third ionization modes can be different from the portions of the survey time period during which the ion source is operated in the second and fourth ionization modes.
The electronic processor can be configured to apply the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during at least one common portion of the survey time period. The electronic processor can be configured to apply the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during the entire survey time period.
The survey time period can be 100 ms or less. The survey time period can be between 50 ms and 100 ms.
The electronic processor is configured to detect ion currents corresponding to each of the at least two ionization modes using the ion detector, where each ion current corresponds to ions generated from sample molecules or particles when the ion source is operated in a different one of the ionization modes, and determine a preferred ionization scheme for the sample molecules or particles based on the ion currents. The electronic processor can be configured to determine a preferred ionization scheme by selecting a preferred ionization mode from among the at least two ionization modes. The electronic processor can be configured to select the preferred ionization mode based on magnitudes of the ion currents.
The electronic processor can be configured to determine the preferred ionization scheme by selecting a set of modes from among the at least two ionization modes. The set of modes can include one ionization mode. The set of modes can include two ionization modes. The set of modes can include the first and second ionization modes. The set of modes can include each of the at least two ionization modes. The at least two ionization modes can include more than two ionization modes, and the set of modes can include two ionization modes.
The electronic processor can be configured to detect ion currents corresponding to each of the at least two ionization modes using the ion detector, where each ion current corresponds to ions generated from sample molecules or particles when the ion source is operated in a different one of the ionization modes, and determine a preferred ionization scheme for the sample molecules or particles based on the ion currents by selecting a set of modes from among the at least two ionization modes. The set of modes can include the third and fourth ionization modes. The set of modes can include the first and third ionization modes. The set of modes can include the second and fourth ionization modes.
The electronic processor can be configured to adjust the ion trap and the ion detector to detect ions corresponding to a range of masses based on the ion currents. The electronic processor can be configured to adjust a duty cycle of the ion source based on the ion currents. The duty cycle of the ion source can be adjusted to a value of 5% or less (e.g., 2% or less).
The systems can include a pump connected to the ion source, the ion trap, the ion detector, and the electronic processor, where the electronic processor is configured to activate the pump to maintain a gas pressure in the ion trap and the ion detector of 1 Torr or more during the survey time period. The electronic processor can be configured to activate the pump to maintain a gas pressure in the ion trap and the ion detector of 10 Torr or more during the survey time period.
The electronic processor can be configured to apply an electrical potential to electrodes of the ion trap to trap the generated ions within the ion trap for a trapping time of 2 ms or less. The electronic processor can be configured to apply an electrical potential to electrodes of the ion trap so that the generated ions are not trapped within the ion trap.
The first and third ranges of masses can correspond to a first common mass range, the second and fourth ranges of masses can correspond to a second common mass range, the electronic processor can be configured to operate the ion source and ion trap in the first and third ionization modes at the same time during a first portion of the survey time period and to operate the ion detector to detect masses within the first common mass range during the first survey time period, and the electronic processor can be configured to operate the ion source and ion trap in the second and fourth ionization modes at the same time during a second portion of the survey time period and to operate the ion detector to detect masses within the second common mass range during the second survey time period.
The electronic processor can be configured to operate the ion source and ion trap again in each of the at least two ionization modes during a second survey time period, to detect ion currents corresponding to each of the at least two ionization modes during the second survey time period using the ion detector, and to determine the preferred ionization scheme based on the ion currents detected during the first and second survey time periods.
The two or more ionization modes can include four ionization modes, where the set of ionization modes includes three or fewer ionization modes, and where the electronic processor is configured to operate the ion source and ion trap again in each one of the set of ionization modes during a second survey time period, and to detect ion currents corresponding to each one of the set of ionization modes during the second survey time period. The electronic processor can be configured to determine the preferred ionization scheme based on the ion currents detected during the second survey time period. The preferred ionization scheme can include each one of the ionization modes from the set of modes. The preferred ionization scheme can include a subset of the set of ionization modes.
Embodiments of the systems can also include any of the other features disclosed herein, including features disclosed in connection with different embodiments, in any combination as appropriate.
In another aspect, the disclosure features methods that include operating an ion source, an ion trap, and an ion detector of a mass spectrometry system in at least two ionization modes during a survey time period of 500 ms or less, where in a first ionization mode of the at least two ionization modes, the ion source generates a plurality of positively charged ions from sample molecules or particles in the system, and in a second ionization mode of the at least two ionization modes, the ion source generates a plurality of negatively charged ions from sample molecules or particles in the system.
Embodiments of the methods can include any one or more of the following features.
In the first ionization mode, the ion detector can detect positively charged ions corresponding to a first range of masses, and in the second ionization mode, the ion detector can detect negatively charged ions corresponding to a second range of masses. The first and second ranges of masses can be different. Alternatively, the first and second ranges of masses can be the same.
The at least two ionization modes can include a third ionization mode, and in the third ionization mode, the ion source can generate a plurality of positively charged ions from sample molecules or particles in the system. In the third ionization mode, the ion detector can detect positively charged ions corresponding to a third range of masses. The third range of masses can be different from the first range of masses. The third range of masses can correspond to masses that are larger than masses corresponding to the first range of masses.
The at least two ionization modes can include a fourth ionization mode, and in the fourth ionization mode, the ion source can generate a plurality of negatively charged ions from sample molecules or particles in the system. In the fourth ionization mode, the ion detector can detect negatively charged ions corresponding to a fourth range of masses. The fourth range of masses can be the same as the third range of masses. Alternatively, the fourth range of masses can be different from the third range of masses. The fourth range of masses can be different from the second range of masses. The fourth range of masses can correspond to masses that are larger than masses corresponding to the second range of masses.
The methods can include applying a first electrical potential to a detection element of the ion detector to detect positively charged ions, and a second electrical potential different from the first electrical potential to the detection element to detect negatively charged ions. The methods can include applying the first electrical potential to the detection element during a first portion of the survey time period, and applying the second electrical potential to the detection element during a second portion of the survey time period that is different from the first portion. The methods can include, during the first portion of the survey time period, operating the ion source in the first ionization mode, and during the second portion of the survey time period, operating the ion source in the second ionization mode.
The methods can include, where the ion detector includes a plurality of detection elements, applying the first electrical potential to each of the detection elements to detect positively charged ions, and applying the second electrical potential to each of the detection elements to detect negatively charged ions. The methods can include applying the first electrical potential to a first subset of the detection elements, and applying the second electrical potential to a second subset of the detection elements. The methods can include applying the first electrical potential to the first subset of the detection elements during a first portion of the survey time period, and applying the second electrical potential to the second subset of the detection elements during a second portion of the survey time period that is different from the first portion. The methods can include, during the first portion of the survey time period, operating the ion source in the first ionization mode, and during the second portion of the survey time period, operating the ion source in the second ionization mode.
The methods can include applying the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during a common portion of the survey time period. The methods can include applying the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during the entire survey time period.
The methods can include: applying a first electrical potential to a detection element of the ion detector to detect positively charged ions, and a second electrical potential different from the first electrical potential to the detection element to detect negatively charged ions; applying the first electrical potential to the detection element during portions of the survey time period in which the ion source is operated in the first and third ionization modes; and applying the second electrical potential to the detection element during portions of the survey time period during which the ion source is operated in the second and fourth ionization modes.
The ion detector can include a plurality of detection elements, and the methods can include applying a first electrical potential to each of the detection elements to detect positively charged ions, and a second electrical potential to each of the detection elements to detect negatively charged ions. The methods can include applying the first electrical potential to a first subset of the detection elements, and the second electrical potential to a second subset of the detection elements. The methods can include applying the first electrical potential to the first subset of the detection elements during portions of the survey time period in which the ion source is operated in the first and third ionization modes, and applying the second electrical potential to the second subset of the detection elements during portions of the survey time period in which the ion source is operated in the second and fourth ionization modes. The portions of the survey time period during which the ion source is operated in the first and third ionization modes can be different from the portions of the survey time period during which the ion source is operated in the second and fourth ionization modes.
The methods can include applying the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during at least one common portion of the survey time period. The methods can include applying the first electrical potential to the first subset of the detection elements and the second electrical potential to the second subset of the detection elements during the entire survey time period.
The survey time period can be 100 ms or less. The survey time period can be between 50 ms and 100 ms.
The methods can include detecting ion currents corresponding to each of the at least two ionization modes using the ion detector, where each ion current corresponds to ions generated from sample molecules or particles when the ion source is operated in a different one of the ionization modes, and determining a preferred ionization scheme for the sample molecules or particles based on the ion currents. The methods can include determining a preferred ionization scheme by selecting a preferred ionization mode from among the at least two ionization modes. The methods can include selecting the preferred ionization mode based on magnitudes of the ion currents.
The methods can include determining the preferred ionization scheme by selecting a set of modes from among the at least two ionization modes. The set of modes can include one ionization mode. The set of modes can include two ionization modes. The set of modes can include the first and second ionization modes. The set of modes can include each of the at least two ionization modes. The at least two ionization modes can include more than two ionization modes, and the set of modes can include two ionization modes.
The methods can include detecting ion currents corresponding to each of the at least two ionization modes using the ion detector, where each ion current corresponds to ions generated from sample molecules or particles when the ion source is operated in a different one of the ionization modes, and determining a preferred ionization scheme for the sample molecules or particles based on the ion currents by selecting a set of modes from among the at least two ionization modes. The set of modes can include the third and fourth ionization modes. The set of modes can include the first and third ionization modes. The set of modes can include the second and fourth ionization modes.
The methods can include adjusting the ion trap and the ion detector to detect ions corresponding to a range of masses based on the ion currents. The methods can include adjusting a duty cycle of the ion source based on the ion currents. The methods can include adjusting the duty cycle of the ion source to a value of 5% or less (e.g., 2% or less).
The methods can include activating a pump connected to the ion source, the ion trap, and the ion detector to maintain a gas pressure in the ion trap and the ion detector of 1 Torr or more during the survey time period. The methods can include activating the pump to maintain a gas pressure in the ion trap and the ion detector of 10 Torr or more during the survey time period.
The methods can include applying an electrical potential to electrodes of the ion trap to trap the generated ions within the ion trap for a trapping time of 2 ms or less. The methods can include applying an electrical potential to electrodes of the ion trap so that the generated ions are not trapped within the ion trap.
The first and third ranges of masses can correspond to a first common mass range and the second and fourth ranges of masses correspond to a second common mass range, and the methods can include operating the ion source and ion trap in the first and third ionization modes at the same time during a first portion of the survey time period and operating the ion detector to detect masses within the first common mass range during the first survey time period, and operating the ion source and ion trap in the second and fourth ionization modes at the same time during a second portion of the survey time period and operating the ion detector to detect masses within the second common mass range during the second survey time period.
The methods can include operating the ion source and ion trap again in each of the at least two ionization modes during a second survey time period, detecting ion currents corresponding to each of the at least two ionization modes during the second survey time period using the ion detector, and determining the preferred ionization scheme based on the ion currents detected during the first and second survey time periods.
The two or more ionization modes can include four ionization modes and the set of ionization modes can include three or fewer ionization modes, and the methods can include operating the ion source and ion trap again in each one of the set of ionization modes during a second survey time period, and detecting ion currents corresponding to each one of the set of ionization modes during the second survey time period. The methods can include determining the preferred ionization scheme based on the ion currents detected during the second survey time period. The preferred ionization scheme can include each one of the ionization modes from the set of modes. The preferred ionization scheme comprises a subset of the set of ionization modes.
Embodiments of the methods can also include any of the other features or steps disclosed herein, including features and steps disclosed in connection with different embodiments, in any combination as appropriate.
In a further aspect, the disclosure features mass spectrometry systems that include an ion source, an ion trap, an ion detector, a pump coupled to the ion source, the ion trap, and the ion detector, and an electronic processor connected to the ion source, the ion trap, the ion detector, and the pump, and configured so that when sample molecules or particles are introduced into the system, the electronic processor analyzes the sample by activating the pump and performing: a first analysis within a survey time period of 10 s or less, where during the first analysis, a gas pressure in at least one of the ion trap and the ion detector is 0.5 Torr or more; and a second analysis, where during the second analysis, a gas pressure in at least one of the ion trap and the ion detector is less than 0.5 Torr.
Embodiments of the systems can include any one or more of the following features.
The electronic processor can be configured so that during the first analysis, the gas pressure in the at least one of the ion trap and the ion detector is 1 Torr or more (e.g., 5 Torr or more). The electronic processor can be configured so that during the second analysis, the gas pressure in the at least one of the ion trap and the ion detector is less than 200 mTorr.
The survey time period can be 1 s or less. The survey time period can be in a range from 50 ms to 100 ms.
During the first analysis, the electronic processor can be configured to determine a preferred ionization scheme for the sample molecules or particles. The electronic processor can be configured to determine the preferred ionization scheme by: operating the ion source to generate positive ions from a first portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to the first portion; operating the ion source to generate negative ions from a second portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to the second portion; and determining the preferred ionization scheme based on the measured ion currents. The electronic processor can be configured to determine the preferred ionization scheme by operating the ion trap and ion detector to measure multiple ion currents corresponding to the first portion, a first one of the multiple ion currents corresponding to a first range of ion masses and a second one of the multiple ion currents corresponding to a second range of ion masses different from the first range. The electronic processor can be configured to determine the preferred ionization scheme by operating the ion trap and ion detector to measure multiple ion currents corresponding to the second portion, a first one of the multiple ion currents corresponding to a third range of ion masses and a second one of the multiple ion currents corresponding to a fourth range of ion masses different from the third range. The first and third ranges can be the same. Alternatively, the first and third ranges can be different. The second and fourth ranges can be the same. Alternatively, the second and fourth ranges can be different.
The electronic processor can be configured to determine the preferred ionization scheme by: operating the ion source to generate positive ions from a first portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a first range of masses of positive ions; operating the ion source to generate positive ions from a second portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a second range of masses of positive ions different from the first range; operating the ion source to generate negative ions from a third portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a third range of masses of negative ions; operating the ion source to generate negative ions from a fourth portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a fourth range of masses of negative ions different from the third range; and determining the preferred ionization scheme based on the measured ion currents.
The preferred ionization scheme can include one or more ionization modes, each ionization mode corresponding to a different combination of electrical potentials applied to electrodes of the ion source to generate ions from the sample molecules or particles, and electrical potentials applied to the ion trap and ion detector to detect ions having a mass within a selected range.
The electronic processor can be configured to perform multiple first analyses of the sample, each within a survey time period of 10 s or less, to determine the preferred ionization scheme for the sample molecules or particles. The survey time period for each successive first analysis of the sample can be the same as, or less then, the survey time period of an immediately preceding first analysis of the sample.
The electronic processor can be configured to perform an intermediate analysis of the sample after the first analysis and before the second analysis, where during the intermediate analysis, the gas pressure in the at least one of the ion trap and the ion detector is 0.5 Torr or more. During the intermediate analysis, the gas pressure in the at least one of the ion trap and the ion detector can be the same as the gas pressure in the at least one of the ion trap and the ion detector during the first analysis. The electronic processor can be configured to operate the ion source, the ion trap, and the ion detector according to the preferred ionization scheme during the intermediate analysis to generate ions from the sample molecules or particles and to detect the generated ions. The electronic processor can be configured to determine information about an environment of the sample based on the ions detected in the intermediate analysis. The information about the sample environment can include information about contaminating species that are present in the sample. The information about the sample environment can include information about matrix materials within the sample.
The electronic processor can be configured to adjust an operating mode of the system based on the information about the environment of the sample. The electronic processor can be configured to adjust the operating mode by changing electrical potentials applied to the ion source. The electronic processor can be configured to adjust the operating mode by changing electrical potentials applied to the ion trap.
The electronic processor can be configured so that during the second analysis, the electronic processor determines information about an identity of the sample. The electronic processor can be configured to determine the information about the identity of the sample by: acquiring a first set of mass spectral information by detecting ions generated from sample molecules or particles; comparing the first set of mass spectral information to reference information to determine candidates representing potential matches to the identity of the sample; acquiring a second set of mass spectral information by detecting ions generated from sample molecules or particles; and analyzing the second set of mass spectral information to distinguish among the candidates and determine the information about the identity of the sample. The electronic processor can be configured to compare the first set of mass spectral information to reference information by analyzing the first set of mass spectral information with a set of matched target detection filters.
Embodiments of the systems can also include any of the other features disclosed herein, including features disclosed in connection with different embodiments, in any combination as appropriate.
In another aspect, the disclosure features methods that include analyzing a sample introduced into a mass spectrometry system featuring a pump coupled to an ion source, an ion trap, and an ion detector by activating the pump and performing: a first analysis within a survey time period of 10 s or less, where during the first analysis, a gas pressure in at least one of the ion trap and the ion detector is 0.5 Torr or more; and a second analysis, where during the second analysis, a gas pressure in at least one of the ion trap and the ion detector is less than 0.5 Torr.
Embodiments of the methods can include any one or more of the following features.
During the first analysis, the gas pressure in the at least one of the ion trap and the ion detector can be 1 Torr or more (e.g., 5 Torr or more). During the second analysis, the gas pressure in the at least one of the ion trap and the ion detector can be less than 200 mTorr.
The survey time period can be 1 s or less. The survey time period can be in a range from 50 ms to 100 ms.
The methods can include, during the first analysis, determining a preferred ionization scheme for the sample molecules or particles. Determining the preferred ionization scheme can include: operating the ion source to generate positive ions from a first portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to the first portion; operating the ion source to generate negative ions from a second portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to the second portion; and determining the preferred ionization scheme based on the measured ion currents. The methods can include determining the preferred ionization scheme by operating the ion trap and ion detector to measure multiple ion currents corresponding to the first portion, a first one of the multiple ion currents corresponding to a first range of ion masses and a second one of the multiple ion currents corresponding to a second range of ion masses different from the first range. The methods can include determining the preferred ionization scheme by operating the ion trap and ion detector to measure multiple ion currents corresponding to the second portion, a first one of the multiple ion currents corresponding to a third range of ion masses and a second one of the multiple ion currents corresponding to a fourth range of ion masses different from the third range. The first and third ranges can be the same. Alternatively, the first and third ranges can be different. The second and fourth ranges can be the same. Alternatively, the second and fourth ranges can be different.
The methods can include determining the preferred ionization scheme by: operating the ion source to generate positive ions from a first portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a first range of masses of positive ions; operating the ion source to generate positive ions from a second portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a second range of masses of positive ions different from the first range; operating the ion source to generate negative ions from a third portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a third range of masses of negative ions; operating the ion source to generate negative ions from a fourth portion of the sample molecules or particles, and operating the ion trap and ion detector to measure an ion current corresponding to a fourth range of masses of negative ions different from the third range; and determining the preferred ionization scheme based on the measured ion currents.
The preferred ionization scheme can include one or more ionization modes, each ionization mode corresponding to a different combination of electrical potentials applied to electrodes of the ion source to generate ions from the sample molecules or particles, and electrical potentials applied to the ion trap and ion detector to detect ions having a mass within a selected range.
The methods can include performing multiple first analyses of the sample, each within a survey time period of 10 s or less, to determine the preferred ionization scheme for the sample molecules or particles. The survey time period for each successive first analysis of the sample can be the same as, or less then, the survey time period of an immediately preceding first analysis of the sample.
The methods can include performing an intermediate analysis of the sample after the first analysis and before the second analysis, wherein during the intermediate analysis, the gas pressure in the at least one of the ion trap and the ion detector is 0.5 Torr or more. During the intermediate analysis, the gas pressure in the at least one of the ion trap and the ion detector can be the same as the gas pressure in the at least one of the ion trap and the ion detector during the first analysis. The methods can include operating the ion source, the ion trap, and the ion detector according to the preferred ionization scheme during the intermediate analysis to generate ions from the sample molecules or particles and to detect the generated ions. The methods can include determining information about an environment of the sample based on the ions detected in the intermediate analysis. The information about the sample environment can include information about contaminating species that are present in the sample. The information about the sample environment can include information about matrix materials within the sample.
The methods can include adjusting an operating mode of the mass spectrometry system based on the information about the environment of the sample. The methods can include adjusting the operating mode by changing electrical potentials applied to the ion source. The methods can include adjusting the operating mode by changing electrical potentials applied to the ion trap.
The methods can include, during the second analysis, determining information about an identity of the sample. Determining the information about the identity of the sample can include: acquiring a first set of mass spectral information by detecting ions generated from sample molecules or particles; comparing the first set of mass spectral information to reference information to determine candidates representing potential matches to the identity of the sample; acquiring a second set of mass spectral information by detecting ions generated from sample molecules or particles; and analyzing the second set of mass spectral information to distinguish among the candidates and determine the information about the identity of the sample. The methods can include comparing the first set of mass spectral information to reference information by analyzing the first set of mass spectral information with a set of matched target detection filters.
Embodiments of the methods can also include any of the other features or steps disclosed herein, including features and steps disclosed in connection with different embodiments, in any combination as appropriate.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the subject matter herein, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims.
Like reference symbols in the various drawings indicate like elements.
I. General Overview
Mass spectrometers that are used for identification of chemical substances are typically large, complex instruments that consume considerable power. Such instruments are frequently too heavy and bulky to be portable, and thus are limited to applications in environments where they can remain essentially stationary. Further, conventional mass spectrometers are typically expensive and require highly trained operators to interpret the spectra of ion formation patterns that the instruments produce to infer the identities of chemical substances that are analyzed.
To achieve high sensitivity and resolution, conventional mass spectrometers typically use a variety of different components that are designed for operation at low gas pressures. For example, conventional ion detectors such as electron multipliers do not operate effectively at pressures above approximately 10 mTorr. As another example, thermionic emitters that are used in conventional ion sources are also best suited for operation at pressures less than 10 mTorr, and generally cannot be used when even moderate concentrations of oxygen are present. Further, conventional mass spectrometers typically include mass analyzers with geometries specifically designed only for operation at pressures of less than 10 mTorr, and in particular, at pressures in the microTorr range. As a result, not only are conventional mass spectrometers configured for operation at low pressures, but conventional mass spectrometers—due to the components they use—generally cannot be operated at higher gas pressures. Higher gas pressures can, for example, destroy certain components of conventional spectrometers. Less dramatically, certain components may simply fail to operate at higher gas pressures, or may operate so poorly that the spectrometers can no longer acquire useful mass spectral information. As a result, mass spectrometers with significantly different configurations and components are needed for operation at high pressures (e.g., pressures larger than 100 mTorr).
To achieve low pressures, conventional mass spectrometers typically include a series of pumps for evacuating the interior volume of a spectrometer. For example, a conventional mass spectrometer can include a rough pump that rapidly reduces the internal pressure of the system, and a turbomolecular pump that further reduces the internal pressure to microTorr values. Turbomolecular pumps are large and consume considerable electrical power. Such considerations are only of secondary importance in conventional mass spectrometers, however; the consideration of primary importance is achieving high resolution in measured mass spectra. By using the foregoing components operating at low pressure, conventional mass spectrometers commonly can achieve resolutions of 0.1 atomic mass units (amu) or better.
In contrast to heavy, bulky conventional mass spectrometers, the compact mass spectrometers disclosed herein are designed for low power, high efficiency operation. To achieve low power operation, the compact mass spectrometers disclosed herein do not include turbomechanical or other power hungry vacuum pumps. Instead, the compact mass spectrometers typically include only a single mechanical pump operating at low frequency, which reduces power consumption significantly.
By using smaller pumps, the compact mass spectrometers disclosed herein typically operate within a pressure range of 100 mTorr to 100 Torr, which is significantly higher than the operating pressure range for conventional mass spectrometers. Conventional mass spectrometers are not modifiable to operate at these higher pressures, because the components used in conventional instruments (e.g., electron multipliers, thermionic emitters, and ion trap) do not function within the pressure range in which the compact mass spectrometers disclosed herein operate. Further, conventional mass spectrometers are generally not modified to operate at higher internal pressures, because doing so typically would result in poorer resolution in the mass spectra measured with such devices. Because obtaining mass spectra with the highest possible resolution is generally the goal when using such devices, there is little reason to modify the devices to provide poorer resolution.
However, the compact mass spectrometers disclosed herein provide different types of information to a user than conventional mass spectrometers. Specifically, the compact mass spectrometers disclosed herein typically report information such as a name of a chemical substance being analyzed, hazard information associated with the substance, and/or a class to which the substance belongs. The compact mass spectrometers disclosed herein can also report, for example, whether the substance either is or is not a particular target substance. Typically, the mass spectra recorded are not displayed to the user unless the user activates a control that causes the display of the spectra. As a result, unlike conventional mass spectrometers, the compact mass spectrometers disclosed herein do not need to obtain mass spectra with the highest possible resolution. Instead, as long as the spectra obtained are of high enough quality to determine the information that is reported to the user, further increases in resolution are not a critical performance criterion.
By operating at lower resolution (typically, mass spectra are obtained at resolutions of between 1 amu and 10 amu), the compact mass spectrometers disclosed herein consume significantly less power than conventional mass spectrometers. For example, the compact mass spectrometers disclosed herein feature miniature ion traps that operate efficiently at pressures from 100 mTorr to 100 Torr to separate ions of different mass-to-charge ratio, while at the same time consuming far less power than conventional mass analyzers such as ion traps due to their reduced size. For example, as the size of a cylindrical ion trap decreases, the maximum voltage applied to the trap to separate ions decreases, and the frequency with which the voltage is applied increases. As a result, the size of inductors and/or resonators used in power supply circuitry is reduced, and the sizes and power consumption requirements of other components used to generate the maximum voltage are also reduced.
Further, the compact mass spectrometers disclosed herein feature efficient ion sources such as glow discharge ionization sources and/or capacitive discharge ionization sources that further reduce power consumption relative to ion sources such as thermionic emitters that are commonly found in conventional mass spectrometers. Efficient, low power detectors such as Faraday detectors are used in the compact mass spectrometers disclosed herein, rather than the more power hungry electron multipliers that are present in conventional mass spectrometers. As a result of these low power components, the compact mass spectrometers disclosed herein operate efficiently and consume relatively small amounts of electrical power. They can be powered by standard battery-based power sources (e.g., Li ion batteries), and are portable with a handheld form factor.
Because they provide high resolution mass spectra directly to the user, conventional mass spectrometers are generally ill-suited for applications that involve mobile scanning of substances by personnel without special training. In particular, for applications such as on-the-spot security scanning in transportation hubs such as airports and train stations, conventional mass spectrometers are impractical solutions. In contrast, such applications instead benefit from mass spectrometers that are compact, require relatively low power to operate, and provide information that can readily be interpreted by personnel without advanced training, as described above. Compact, low cost mass spectrometers are also useful for a variety of other applications. For example, such devices can be used in laboratories to provide rapid characterization of unknown chemical compounds. Due to their low cost and tiny footprint, laboratories can provide workers with personal spectrometers, reducing or eliminating the need to schedule analysis time at a centralized mass spectrometry facility. Compact mass spectrometers can also be used for applications such as medical diagnostics testing, both in clinical settings and in residences of individual patients. Technicians performing such testing can readily interpret the information provided by such spectrometers to provide real-time feedback to patients, and also to provide rapidly updated information to medical facilities, physicians, and other health care providers.
This disclosure features compact, low power mass spectrometers that provide a variety of information to users including identification of chemical substances scanned by the spectrometers and/or associated contextual information, including information about a class to which substances belong (e.g., acids, bases, strong oxidizers, explosives, nitrated compounds), information about hazards associated with the substances, and safety instructions and/or information. The spectrometers operate at internal gas pressures that are higher than conventional mass spectrometers. By operating at higher pressures, the size and power consumption of the compact mass spectrometers is significantly reduced relative to conventional mass spectrometers. Moreover, even though the spectrometers operate at higher pressures, the resolution of the spectrometers is sufficient to permit accurate identification and quantification of a wide variety of chemical substances.
Controller 108 is connected to ion source 102, ion trap 104, detector 118, pressure regulation subsystem 120, voltage source 106, valve 129, and optional buffer gas source 150 via control lines 127a-127g, respectively. Control lines 127a-127g permit controller 108 (e.g., electronic processor 110 in controller 108) to issue operating commands to each of the components to which it is connected. Such commands can include, for example, signals that activate ion source 102, ion trap 104, detector 118, pressure regulation subsystem 120, valve 129, and buffer gas source 150. Commands that activate the various components of spectrometer 100 can include instructions to voltage source 106 to apply electrical potentials to elements of the components. For example, to activate ion source 102, controller 108 can transmit instructions to voltage source 106 to apply electrical potentials to electrodes in ion source 102. As another example, to activate ion trap 104, controller 108 can transmit instructions to voltage source 106 to apply electrical potentials to electrodes in ion trap 104. As a further example, to activate detector 118, controller 108 can transmit instructions to voltage source 106 to apply electrical potentials to detection elements in detector 118. Controller 108 can also transmit signals to activate pressure regulation subsystem 120 (e.g., through voltage source 106) to control the gas pressure in the various components of spectrometer 100, and to valve 129 (e.g., through voltage source 106) to allow gas particles to enter spectrometer 100 through sample inlet 124.
Further, controller 108 can receive signals from each of the components of spectrometer 100 through control lines 127a-127g. For example, such signals can include information about the operational characteristics of ion source 102 and/or ion trap 104 and/or detector 118 and/or pressure regulation subsystem 120. Controller 108 can also receive information about ions detected by detector 118. The information can include ion currents measured by detector 118, which are related to abundances of ions with specific mass-to-charge ratios. The information can also include information about specific voltages applied to electrodes of ion trap 104 as particular ion abundances are measured by detector 118. The specific applied voltages are related to specific values of mass-to-charge ratio for the ions. By correlating the voltage information with the measured abundance information, controller 108 can determine abundances of ions as a function of mass-to-charge ratio, and can present this information using display 116 in the form of mass spectra.
Voltage source 106 is connected to ion source 102, ion trap 104, detector 118, pressure regulation subsystem 120, and controller 108 via control lines 126a-e, respectively. Voltage source 106 provides electrical potentials and electrical power to each of these components through control lines 126a-e. Voltage source 106 establishes a reference potential that corresponds to an electrical ground at a relative voltage of 0 Volts. Potentials applied by voltage source 106 to the various components of spectrometer 100 are referenced to this ground potential. In general, voltage source 106 is configured to apply potentials that are positive and potentials that are negative, relative to the reference ground potential, to the components of spectrometer 100. By applying potentials of different signs to these components (e.g., to the electrodes of the components), electric fields of different signs can be generated within the components, which cause ions to move in different directions. Thus, by applying suitable potentials to the components of spectrometer 100, controller 108 (through voltage source 106) can control the movement of ions within spectrometer 100.
Ion source 102, ion trap 104, and detector 118 are connected such that an internal pathway for gas particles and ions, gas path 128, extends between these components. Sample inlet 124 and pressure regulation subsystem 120 are also connected to gas path 128. Optional buffer gas source 150, if present, is connected to gas path 128 as well. Portions of gas path 128 are shown schematically in
The trapped ions circulate within ion trap 104. To analyze the circulating ions, voltage source 106, under the control of controller 108, varies the amplitude of a radiofrequency trapping field applied to one or more electrodes of ion trap 104. The variation of the amplitude occurs repetitively, defining a sweep frequency for ion trap 104. As the amplitude of the field is varied, ions with specific mass-to-charge ratios fall out of orbit and some are ejected from ion trap 104. The ejected ions are detected by detector 118, and information about the detected ions (e.g., measured ion currents from detector 118, and specific voltages that are applied to ion trap 104 when particular ion currents are measured) is transmitted to controller 108.
Although sample inlet 124 is positioned in
Communication interface 117 can, in general, be a wired or wireless communication interface (or both). Through communication interface 117, controller 108 can be configured to communicate with a wide variety of devices, including remote computers, mobile phones, and monitoring and security scanners. Communication interface 117 can be configured to transmit and receive data over a variety of networks, including but not limited to Ethernet networks, wireless WiFi networks, cellular networks, and Bluetooth wireless networks. Controller 108 can communicate with remote devices using communication interface 117 to obtain a variety of information, including operating and configuration settings for spectrometer 100, and information relating to substances of interest, including records of mass spectra of known substances, hazards associated with particular substances, classes of compounds to which substances of interest belong, and/or spectral features of known substances. This information can be used by controller 108 to analyze sample measurements. Controller 108 can also transmit information to remote devices, including alerting messages when certain substances (e.g., hazardous and/or explosive substances) are detected by spectrometer 100.
The mass spectrometers disclosed herein are both compact and capable of low power operation. To achieve both compact size and low power operation, the various spectrometer components, including ion source 102, ion trap 104, detector 118, pressure regulation subsystem 120, and voltage source 106, are carefully designed and configured to minimize space requirements and power consumption. In conventional mass spectrometers, the vacuum pumps used to achieve low internal operating pressures (e.g., 1×10−3 Torr or considerably less) are both large and consume significant amounts of electrical power. For example, to reach such pressures, conventional mass spectrometers typically employ a series of two or more pumps, including a rough pump that rapidly reduces the internal system pressure from atmospheric pressure to about 0.1-10 Torr, and one or more turbomolecular pumps that reduce the internal system pressure from 10 Torr to the desired internal operating pressure. Both rough pumps and turbomolecular pumps are mechanical pumps that require significant quantities of electrical power to run. Rough pumps (which can include, for example, piston-based pumps) typically generate significant mechanical vibrations. Turbomolecular pumps are typically sensitive to both vibrations and mechanical shocks, and produce effects that are similar to a gyroscope due to their high rotational speeds. As a result, conventional mass spectrometers include power sources sufficient to meet the consumption requirements of their vacuum pumps, and isolation mechanisms (e.g., vibrational and/or rotational isolation mechanisms) to ensure that these pumps remain operating. Conventional mass spectrometers may even require that while operating, the turbomolecular pumps therein cannot be moved, as doing so may result in mechanical vibrations that would destroy these pumps. As a result, the combination of vacuum pumps and electrical power sources used in conventional mass spectrometers makes them large, heavy, and immobile.
In contrast, the mass spectrometer systems and methods disclosed herein are compact, mobile, and achieve low power operation. These characteristics are realized in part by eliminating the turbomolecular, rough, and other large mechanical pumps that are common to conventional spectrometers. In place of these large pumps, small, low power single mechanical pumps are used to control gas pressure within the mass spectrometer systems. The single mechanical pumps used in the mass spectrometer systems disclosed herein cannot reach pressures as low as conventional turbomolecular pumps. As a result, the systems disclosed herein operate at higher internal gas pressures than conventional mass spectrometers.
As will be explained in greater detail below, operating at higher pressure generally degrades the resolution of a mass spectrometer, due to a variety of mechanisms such as collision-induced line broadening and charge exchange among molecular fragments. As used herein, “resolution” is defined as the full width at half-maximum (FWHM) of a measured mass peak. The resolution of a particular mass spectrometer is determined by measuring the FWHM for all peaks that appear within the range of mass-to-charge ratios from 100 to 125 amu, and selecting the largest FWHM that corresponds to a single peak (e.g., peak widths that correspond to closely spaced sets of two or more peaks are excluded) as the resolution. To determine the resolution, a chemical substance with a well known mass spectrum, such as toluene, can be used.
While the resolution of a mass spectrometer may be degraded when operating at higher pressures, the mass spectrometers disclosed herein are configured so that reduced resolution does not compromise the usefulness of the spectrometers. Specifically, the mass spectrometers disclosed herein are configured so that when a chemical substance of interest is scanned using a spectrometer, the spectrometer reports to the user information relating to an identity of the substance, rather than a mass-resolved spectrum of molecular ions, as is common in conventional mass spectrometers. In some embodiments, the algorithms used in the mass spectrometers disclosed herein can compare measured ion fragmentation patterns to information about known fragmentation patterns to determine information such as an identity of the substance of interest, hazard information relating to the substance of interest, and/or one or more classes of compounds to which the substance of interest belongs. In certain embodiments, the algorithms can include expert systems to determine information about the identity of the substance of interest. For example, digital filters can be used to search for particular features in measured spectra for a substance of interest, and the substance can be identified as corresponding to a particular target substance or not corresponding to the target substance based on the presence or absence of the features in the spectra.
When controller 108 performs the foregoing analyses, reduced resolution due to operation at high pressure can be compensated for by the systems disclosed herein. That is, provided a reliable correspondence between a measured fragmentation pattern and reference information can be achieved, the lower resolution due to high pressure operation is of little consequence to users of the mass spectrometers disclosed herein. Thus, even though the mass spectrometers disclosed herein operate at higher pressures than conventional mass spectrometers, they remain useful for a wide variety of applications such as security scanning, medical diagnostics, and laboratory analysis, in which the user is primarily concerned with identifying a substance of interest rather than examining the substance's ion fragmentation pattern in detail, and where the user may not have advanced training in the interpretation of mass spectra.
By using a single, small mechanical pump, the weight, size, and power consumption of the mass spectrometers disclosed herein is substantially reduced relative to conventional mass spectrometers. Thus, the mass spectrometers disclosed herein generally include pressure regulation subsystem 120, which features a small mechanical pump, and which is configured to maintain an internal gas pressure (e.g., a gas pressure in gas path 128, and in ion source 102, ion trap 104, and detector 118, all of which are connected to gas path 128) of between 100 mTorr and 100 Torr (e.g., between 100 mTorr and 500 mTorr, between 500 mTorr and 100 Torr, between 500 mTorr and 10 Torr, between 500 mTorr and 5 Torr, between 100 mTorr and 1 Torr). In some embodiments, the pressure regulation subsystem is configured to maintain an internal gas pressure in the mass spectrometers disclosed herein of more than 100 mTorr (e.g., more than 500 mTorr, more than 1 Torr, more than 10 Torr, more than 20 Torr).
At the foregoing pressures, the mass spectrometers disclosed herein detect ions at a resolution of 10 amu or better. For example, in some embodiments, the resolution of the mass spectrometers disclosed herein, measured as described above, is 10 amu or better (e.g., 8 amu or better, 6 amu or better, 5 amu or better, 4 amu or better, 3 amu or better, 2 amu or better, 1 amu or better). In general, any of these resolutions can be achieved at any of the foregoing pressures using the mass spectrometers disclosed herein.
In addition to a pump, pressure regulation subsystem 120 can include a variety of other components. In some embodiments, pressure regulation subsystem 120 includes one or more pressure sensors. The one or more pressure sensors can be configured to measure gas pressure in a fluid conduit to which pressure regulation subsystem 120 is connected, e.g., gas path 128. Measurements of gas pressure can be transmitted to a pump within pressure regulation subsystem 120, and/or to controller 108, and can be displayed on display 116. In certain embodiments, pressure regulation subsystem 120 can include other elements for fluid handling such as one or more valves, apertures, sealing members, and/or fluid conduits.
To ensure that the pressure regulation subsystem functions efficiently to control the internal pressure in the mass spectrometers disclosed herein, the internal volume of the spectrometers (e.g., the volume that is pumped by the pressure regulation subsystem) is significantly reduced relative to the internal volume of conventional mass spectrometers. Reducing the internal volume has the added benefit of reducing the overall size of the mass spectrometers disclosed herein, making them compact, portable, and capable of one-handed operation by a user.
As shown in
In some embodiments, the mass spectrometers disclosed herein are fully integrated on a single support base.
Integration on a single support base such as a printed circuit board provides a number of important advantages. Support base 140 provides a stable platform for the components of spectrometer 100, ensuring that each of the components is mounted stably and securely, and reducing the likelihood that components will be damaged during rough handling of spectrometer 100. In addition, mounting all components on a single support base simplifies manufacturing of spectrometer 100, as support base 140 provides a reproducible template for the positioning and connection of the various components to one another. Further, by integrating all of the control lines onto the support base, such that both electrical power and control signals are transmitted between components through support base 140, the integrity of the electrical connections between components can be maintained—such connections are less susceptible to wear and/or breakage than connections formed by individual wires extending between components.
Further, by integrating the components of spectrometer 100 onto a single support base, spectrometer 100 has a compact form factor. In particular, a maximum dimension of support base 140 (e.g., a largest linear distance between any two points on support base 140) can be 25 cm or less (e.g., 20 cm or less, 15 cm or less, 10 cm or less, 8 cm or less, 7 cm or less, 6 cm or less).
As shown in
In some embodiments, the mass spectrometers disclosed herein include a pluggable, replaceable module in which multiple system components are integrated.
Module 148 also includes a plurality of electrodes 142 that extend outward from the module. Within module 148, electrodes 142 are connected to each of the components within the module, e.g., to ion source 102, ion trap 104, and detector 118.
Also shown in
Electrodes 144 of support base 140 are connected to controller 108 and voltage source 106, as shown in
Pressure regulation subsystem 120, which is mounted to support base 140, is connected to a manifold 121 via conduit 123 Manifold 121, which includes one or more apertures 125, is positioned on support base 140 so that when module 148 is connected to support base 140, a sealed fluid connection is established between manifold 121 and module 148. In particular, a fluid connection is established between apertures 125 in manifold 121 and corresponding apertures in module 148 (not shown in
Other configurations of module 148 are also possible. In some embodiments, for example, detector 118 is not part of module 148, and is instead mounted to support base 140. In such a configuration, detector 118 is positioned on support base 140 so that when module 148 is connected to support base 140, a sealed fluid connection is established between ion trap 104 and detector 118. Establishing a sealed fluid connection allows circulating ions within ion trap 104 to be ejected from the trap and detected using detector 118, and also allows pressure regulation subsystem 120 to maintain reduced gas pressure (e.g., between 100 mTorr and 100 Torr) in detector 118.
In certain embodiments, pressure regulation subsystem 120 can be integrated into module 148. For example, pressure regulation subsystem 120 can be attached to the underside of ion trap 104 and connected directly to gas path 128 within module 148. Pressure regulation subsystem 120 is also electrically connected to electrodes 142 of module 148. When module 148 is connected to support base 140, pressure regulation subsystem 120 can transmit and receive electrical signals to/from controller 108 and voltage source 106 through electrodes 142.
The modular configuration of mass spectrometer 100 shown in
The modular configuration shown in
A module 148 with reduced functionality (e.g., a module that has become contaminated with analyte particles that adhere to interior walls of ion source 102, ion trap 104, and/or detector 118) can be regenerated and returned to use. In some embodiments, to return a module 148 to normal operation, the module can be heated while it is installed within spectrometer 100. Heating can be accomplished using a heating element 127 mounted on support base 140. As shown in
Controller 108 can be configured to activate heating element 127 by directing voltage source 106 to apply suitable electrical potentials to heating element 127. Commencement of heating, and the temperature and duration of heating, can be controlled by a user of spectrometer 100, e.g., by activating a control on display 116 and/or by entering user configuration settings into storage unit 114. In certain embodiments, controller 108 can be configured to determine automatically when regeneration of module 148 is appropriate. For example, controller 108 can monitor detected ion currents over a period of time, and if the ion current falls by more than a threshold amount (e.g., 25% or more, 50% or more, 60% or more, 70% or more) within a particular time period (e.g., 1 hour or more, 5 hours or more, 10 hours or more, 24 hours or more, 2 days or more, 5 days or more, 10 days or more), then controller 108 determines that regeneration of module 148 is needed.
Although heating element 127 is mounted on support base 140 in
In certain embodiments, module 148 can be removed from spectrometer 100 for regeneration. For example, when module 148 exhibits reduced functionality (e.g., as determined by a user of spectrometer 100, or as determined automatically by controller 108 using the above criteria), module 148 can be removed from spectrometer 100 and heated to restore it to normal operating condition. Heating can be accomplished in a variety of ways, including heating in general purpose ovens. In some embodiments, spectrometer 100 can include a dedicated plug-in heater that includes a slot configured to receive module 148. When a module is inserted into the slot and the heater is activated, the module is heated to restore its functionality.
While ion source 102, ion trap 104, and detector 118 are generally configured to detect and identify a wide variety of chemical substances, in certain embodiments these components can be specifically tailored for detection of certain classes of substances. In some embodiments, ion source 102 can be specifically configured for use with certain substances. For example, different electrical potentials can be applied to the electrodes of ion source 102 to generate either positive or negative ions from gas particles. Further, the magnitudes of the electrical potentials applied to the electrodes of ion source 102 can be varied to control the efficiency with which certain substances ionize. In general, different substances have different affinities for ionization depending upon their chemical structure. By adjusting the polarity and the electrical potential difference between electrodes of ion source 102, ionization of a variety of substances can be carefully controlled.
In certain embodiments, ion trap 104 can be specifically configured for use with certain substances. For example, the internal dimensions (e.g., the internal diameter) of ion trap 104 can be selected to favor trapping and detection of ions with higher mass-to-charge ratio.
In some embodiments, internal gas pressures within one or more of ion source 102, ion trap 104, and detector 118 can be selected to favor softer or harder ionization mechanisms, or positive or negative ion generation. Further, the magnitudes and polarities of the electrical potentials applied to the electrodes of ion source 102 and ion trap 104 can be selected to favor certain ionization mechanisms. As discussed above, different substances have different affinities for ionization, and may ionize more efficiently in one manner (e.g., according to one mechanism) than another. By adjusting the gas pressures and electrical potentials applied to various electrodes within spectrometer 100, the spectrometer can be adapted to specifically detect a wide variety of substances and classes of substances. In addition, by adjusting the geometry of ion trap 104 and/or the electrical potentials applied to its electrodes, the mass window of ion trap 104 (e.g., the range of ion mass-to-charge ratios that can be maintained in circulating orbit within ion trap 104) can be selected.
In certain embodiments, ion source 102 can include a particular type of ionizer tailored for certain types of substances. For examples, ionization sources based on glow discharge ionization, electrospray mass ionization, capacitive discharge ionization, dielectric barrier discharge ionization, and any of the other ionizer types disclosed herein can be used in ion source 102.
In some embodiments, detector 118 can be specifically tailored for certain types of detection tasks. For example, detector 118 can any one or more of the detectors disclosed herein. The detectors can be arranged in specific configurations, e.g., in array form, with a plurality of detection elements such as a plurality of Faraday cup detectors, as will be discussed subsequently, and/or in any arrangement within detector 118. In addition to being tailored for detection of certain substances, detector 118 can also be tailored for use with certain types of ion sources and ion traps. For example, the arrangement and types of detection elements within detector 118 can be selected to correspond to the arrangement of ion chambers within ion trap 104, particularly where ion trap 104 includes multiple ion chambers.
In certain embodiments, one or more internal surfaces of module 148 (e.g., of ion source 102 and/or ion trap 104 and/or detector 118) can include one or more coatings and/or surface treatments. The coatings and/or surface treatments can be adapted for specific applications, including detection of specific types of substances, operation within specific gas pressure ranges, and/or operation at certain applied electrical potentials. Examples of coatings and surface treatments that can be used to tailor module 148 for specific substances and/or applications include Teflon® (more generally, fluorinated polymer coatings), anodized surfaces, nickel, and chrome.
Other components of module 148 can also be adapted to detect specific substances or classes of substances. For example, sample inlet 124 can be equipped with a filter (e.g., filter 706 in
Accordingly, in some embodiments, mass spectrometer 100 can include multiple replaceable modules 148. Some of the modules can be the same, and can function as direct replacements for one another (e.g., in the event of contamination). Other modules can be configured for different modes of operation. For example, the multiple replaceable modules 148 can be configured to detect different classes of substances. A user operating spectrometer 100 can select a suitable module for a particular class of substances, and can plug in the selected module to support base 140 prior to initiating an analysis. To analyze a different class of substances, the user can disengage the first module from support base 140, select a new module, and plug in the new module to support base 140. As a result, re-configuring the components of mass spectrometer 100 for a variety of different applications is rapid and straightforward. Modules can also be specifically configured to different types of measurements (e.g, using different ionization methods, different trapping and/or ejection potentials applied to the electrodes of ion trap 104, and/or different detection methods). In general, each of the multiple replaceable modules 148 can include any of the features disclosed herein. Thus, some of the modules can differ based on their ion sources, some of the modules can differ based on their ion traps, and some of the modules can differ based on their detectors. Certain modules may differ from one another based on more than one of these components.
In some embodiments, one or more attachment mechanisms can be used to secure module 148 to support base 140. Referring to
In certain embodiments, attachment mechanisms 195 and 197 can be keyed so that module 148 will only connect to support base 140 in a single orientation. Keying the attachment mechanisms has the advantage that it prevents a user from installing module 148 in an incorrect orientation.
In some embodiments, other attachment mechanisms can be used. For example, support base 140 and/or module 148 can include a clamp 199 that fixes module 148 to support base 140. One or more clamps can be used. In addition, clamps can be used in addition to other attachment mechanisms.
In the following sections, the various components of mass spectrometer 100 will be discussed in greater detail, and various operating modes of spectrometer 100 will also be discussed.
II. Ion Source
In general, ion source 102 is configured to generate electrons and/or ions. Where ion source 102 generates ions directly from gas particles that are to be analyzed, the ions are then transported from ion source 102 to ion trap 104 by suitable electrical potentials applied to the electrodes of ion source 102 and ion trap 104. Depending upon the magnitude and polarity of the potentials applied to the electrodes of ion source 102 and the chemical structure of the gas particles to be analyzed, the ions generated by ion source 102 can be positive or negative ions. In some embodiments, electrons and/or ions generated by ion source 102 can collide with neutral gas particles to be analyzed to generate ions from the gas particles. During operation of ion source 102, a variety of ionization mechanisms can occur at the same time within ion source 102, depending upon the chemical structure of the gas particles to be analyzed and the operating parameters of ion source 102.
By operating at higher internal gas pressures than conventional mass spectrometers, the compact mass spectrometers disclosed herein can use a variety of ion sources. In particular, ion sources that are small and that require relatively modest amounts of electrical power to operate can be used in spectrometer 100. In some embodiments, for example, ion source 102 can be a glow discharge ionization (GDI) source. In certain embodiments, ion source 102 can be a capacitive discharge ion source.
A variety of other types of ion sources can also be used in spectrometer 100, depending upon the amount of power required for operation and their size. For example, other ion sources suitable for use in spectrometer 100 include dielectric barrier discharge ion sources and thermionic emission sources. As a further example, ion sources based on electrospray ionization (ESI) can be used in spectrometer 100. Such sources can include, but are not limited to, sources that employ desorption electrospray ionization (DESI), secondary ion electrospray ionization (SESI), extractive electrospray ionization (EESI), and paper spray ionization (PSI). As yet another example, ion sources based on laser desorption ionization (LDI) can be used in spectrometer 100. Such sources can include, but are not limited to, sources that employ electrospray-assisted laser desorption ionization (ELDI), and matrix-assisted laser desorption ionization (MALDI). Still further, ion sources based on techniques such as atmospheric solid analysis probe (ASAP), desorption atmospheric pressure chemical ionization (DAPCI), desorption atmospheric pressure photoionization (DAPPI), and sonic spray ionization (SSI) can be used in spectrometer 100. Ion sources based on arrays of nanofibers (e.g., arrays of carbon nanofibers) are also suitable for use. Other aspects and features of the foregoing ion sources, and other examples of ion sources suitable for use in spectrometer 100, are disclosed, for example, in the following publications, the entire contents of each of which is incorporated by reference herein: Alberici et al., “Ambient mass spectrometry: bringing MS into the ‘real world,’” Anal. Bioanal. Chem. 398: 265-294 (2010); Harris et al. “Ambient Sampling/Ion Mass Spectrometry: Applications and Current Trends,” Anal. Chem. 83: 4508-4538 (2011); and Chen et al., “A Micro Ionizer for Portable Mass Spectrometers using Double-gated Isolated Vertically Aligned Carbon Nanofiber Arrays,” IEEE Trans. Electron Devices 58(7): 2149-2158 (2011).
GDI sources are particularly advantageous for use in spectrometer 100 because they are compact and well suited for low power operation. The glow discharge that occurs when these sources are active occurs only when gas pressures are sufficient, however. Typically, for example, GDI sources are limited in operation to gas pressures of approximately 200 mTorr and above. At pressures lower than 200 mTorr, sustaining a stable glow discharge can be difficult. As a result, GDI sources are not used in conventional mass spectrometers, which operate at pressures of 1 mTorr or less. However, because the mass spectrometers disclosed herein typically operate at gas pressures of between 100 mTorr and 100 Torr, GDI sources can be used.
As shown in
Aperture 202 is surrounded by an insulating tube 204. In
In some embodiments, additional gas particles can be introduced into GDI source 200 to assist in the generation of electrons and/or ions in the source. For example, as explained above in connection with
Alternatively, in some embodiments, a mixture of gas particles that includes the gas particles to be analyzed and atmospheric gas particles are the only gas particles that are introduced into GDI chamber 230. In such embodiments, only the gas particles to be analyzed may be ionized in GDI chamber 230. In certain embodiments, both the gas particles to be analyzed and admitted atmospheric gas particles may be ionized in GDI chamber 230.
Although aperture 202 is positioned in the center of the front electrode 210 in
Thus, depending upon where the gas particles to be analyzed are introduced intro spectrometer 100 (e.g., the position of sample inlet 124), ions can be generated from the gas particles at a variety of different locations. Ion generation can occur directly in ion source 102, and the generated ions can be transported into ion trap 104 by applying suitable electrical potentials to the electrodes of ion source 102 and ion trap 104. Ion generation can also occur within ion trap 104, when charged particles such as ions (e.g., buffer gas ions) and electrons generated by ion source 102 enter ion trap 104 and collide with gas particles to be analyzed. Ion generation can occur in multiple places at once (e.g., in both ion source 102 and ion trap 104), with all of the generated ions eventually becoming trapped within ion trap 104. Although the discussion in this section focuses largely on direct generation of ions from gas particles of interest within ion source 102, the aspects and features disclosed herein are also applicable generally to the secondary generation of ions from gas particles of interest in other components of spectrometer 100.
A variety of different spacings between electrodes 210 and 220 can be used. In general, the efficiency with which ions are generated is determined by a number of factors, including the potential difference between electrodes 210 and 220, the gas pressure within GDI source 200, the distance 234 between electrodes 210 and 220, and the chemical structure of the gas particles that are ionized. Typically, distance 234 is relatively small to ensure that GDI source 200 remains compact. In some embodiments, for example, distance 234 between electrodes 210 and 220 is be 1.5 cm or less (e.g., 1 cm or less, 0.75 cm or less, 0.5 cm or less, 0.25 cm or less, 0.1 cm or less).
The gas pressure in GDI chamber 230 is generally regulated by pressure regulation subsystem 120. In some embodiments, the gas pressure in GDI chamber 230 is approximately the same as the gas pressure in ion trap 104 and/or detector 118. In certain embodiments, the gas pressure in GDI chamber 230 differs from the gas pressure in ion trap 104 and/or detector 118. Typically, the gas pressure in GDI chamber 230 is 100 Torr or less (e.g., 50 Torr or less, 20 Torr or less, 10 Torr or less, 5 Torr or less, 1 Torr or less, 0.5 Torr or less) and/or 100 mTorr or more (e.g., 200 mTorr or more, 300 mTorr or more, 500 mTorr or more, 1 Torr or more, 10 Torr or more, 20 Torr or more).
During operation, GDI source 200 generates a self-sustaining glow discharge (or plasma) when a voltage difference is applied between front electrode 210 and back electrode 220 by voltage source 106 under the control of controller 108. In some embodiments, the voltage difference can be 200V or higher (e.g., 300V or higher, 400V or higher, 500V or higher, 600V or higher, 700V or higher, 800V or higher) to sustain the glow discharge. As discussed above, detector 118 detects the ions generated by GDI source 200, and the potential difference between electrodes 210 and 220 can be adjusted by controller 108 to control the rate at which ions are generated by GDI source 200.
In some embodiments, GDI source 200 is directly mounted to support base 140, and electrodes 210 and 220 are directly connected to voltage source 106 through support base 140, as shown in
By applying electrical potentials of differing polarity relative to the ground potential established by voltage source 106. GDI source 200 can be configured to operate in different ionization modes. For example, during typical operation of GDI source 200, a small fraction of gas particles is initially ionized in GDI chamber 230 due to random processes (e.g., thermal collisions). In some embodiments, electrical potentials are applied to front electrode 210 and back electrode 220 such that front electrode 210 serves as the cathode and back electrode 220 serves as the anode. In this configuration, positive ions generated in GDI chamber 230 are driven towards the front electrode 210 due to the electric field within the chamber. Negative ions and electrons are driven towards the back electrode 220. The electrons and ions can collide with other gas particles, generating a larger population of ions. Negative ions and/or electrons exit GDI chamber 230 through the back electrode 220.
In certain embodiments, suitable electrical potentials are applied to front electrode 210 and back electrode 220 so that front electrode 210 serves as the anode and back electrode 220 serves as the cathode. In this configuration, positively charged ions generated in GDI chamber 230 leave the chamber through back electrode 220. The positively charged ions can collide with other gas particles, generating a larger population of ions.
In some embodiments, user interface 112 can include a control that allows a user to select one of the above ionization modes. The selection of an appropriate ionization mode can depend upon the nature of the substance to be analyzed by spectrometer 100. Certain substances are more efficiently ionized as positive ions, and the operating mode can be chosen such that back electrode 220 functions as the cathode. Positive ions generated while operating in this mode exit GDI source 200 through back electrode 220. Alternatively, certain substances are more efficiently ionized as negative ions, and the operating mode can be chosen such that back electrode 220 functions as the anode. Negative ions generated while operating in this mode exit GDI source 200 through back electrode 220. In general, controller 108 is configured to monitor ion currents measured by detector 118, and to select a suitable operating mode for GDI source based on the ion currents. Alternatively, or in addition, a user of spectrometer 100 can select a suitable operating mode using a control displayed on user interface 114, or by entering appropriate configuration settings into storage unit 114 of spectrometer 100.
After ions are generated and leave GDI chamber 230 through back electrode 220 in either operating mode, the ions enter ion trap 104 through end cap electrode 304. In general, back electrode 220 can include one or more apertures 240. The number of apertures 240 and their cross-sectional shapes are generally chosen to create a relatively uniform spatial distribution of ions incident on end cap electrode 304. As the ions generated in GDI chamber 230 leave the chamber through the one or more apertures 240 in back electrode 220, the ions spread out spatially from one another due to collisions and space-charge interactions. As a result, the overall spatial distribution of ions leaving GDI source 200 diverges. By selecting a suitable number of apertures 240 having particular cross-sectional shapes, the spatial distribution of ions leaving GDI source 200 can be controlled so that the distribution overlaps or fills all of the apertures 292 formed in end cap electrode 304. In some embodiments, an additional ion optical element (e.g., an ion lens) can be positioned between back electrode 220 and end cap electrode 304 to further manipulate the spatial distribution of ions emerging from GDI source 200. However, a particular advantage of the compact ion sources disclosed herein is that suitable ion distributions can be obtained without any additional elements between back electrode 220 and end cap electrode 304.
In some embodiments, back electrode 220 includes a single aperture 240. The cross-sectional shape of aperture 240 can be circular, square, rectangular, or can correspond more generally to any regularly or irregularly shaped n-sided polygon. In certain embodiments, the cross-sectional shape of aperture 240 can be irregular.
In some embodiments, back electrode 220 includes more than one aperture 240. In general, back electrode 220 can include any number of apertures (e.g., 2 or more, 4 or more, 8 or more, 16 or more, 24 or more, 48 or more, 64 or more, 100 or more, 200 or more, 300 or more, 500 or more), spaced by any amount, provided that back electrode 220 remains mechanically stable enough to use in GDI source 200.
As shown in
More generally, end cap electrode 304 can include multiple apertures 294. The types of apertures, their arrangements, and the criteria for selecting particular types of apertures for end cap electrode 304 are, in general, similar to the types, arrangements, and criteria discussed above in connection with back electrode 220. Accordingly, the foregoing discussion applies equally to apertures 294 formed in end cap electrode 304.
As shown in
More particularly, as shown for example in
In some embodiments, the pattern of apertures 240 formed in back electrode 220 exactly matches the pattern of apertures 294 formed in end cap electrode 304, i.e., there is a one-to-one correspondence between the apertures. In general, as the extent to which the apertures are matched in back electrode 220 and end cap electrode 304 increases, distance 244 between back electrode 220 and end cap electrode 304 can be reduced, because ions emerging from back electrode 220 more uniformly fill apertures 294 in end cap electrode 304. When the matching of apertures between the electrodes is exact or nearly exact, distance 244 can even be reduced to zero (i.e., back electrode 220 can be positioned directly adjacent to end cap electrode 304), making GDI source 200 highly compact. Further, as the extent of matching between apertures increases, the number of ions entering apertures 294 can be maximized by reducing the number of ions that strike portions of end cap electrode 304 between the apertures. As a result, the ion collection efficiency of ion trap 104 is increased. Further, by increasing the efficiency with which ions generated by ion source 102 are collected within ion trap 104, the overall sizes of back electrode 220 and end cap electrode 304 can be reduced relative to single aperture electrodes and/or electrodes with unmatched apertures.
In some embodiments, back electrode 220 and end cap electrode 304 can be formed as a single element, and ions formed in GDI chamber 230 can directly enter the ion trap 104 by passing through the element. In such embodiments, the combined back and end cap electrode can include a single aperture or multiple apertures, as described above.
Further, in certain embodiments, the end cap electrodes of ion trap 104 can function as the front electrode 210 and the back electrode 220 of GDI source 200. As will be discussed in more detail subsequently, ion trap 104 includes two end cap electrodes 304 and 306 positioned on opposite sides of the trap. By applying suitable potentials (e.g., as described above with reference to front electrode 210 and back electrode 220) to these electrodes, end cap electrode 304 can function as front electrode 210, and end cap electrode 306 can function as back electrode 220. Accordingly, in these embodiments, ion trap 104 also functions as a glow discharge ion source 102.
Various operating modes can be used to generate charged particles in GDI source 200. For example, in some embodiments, a continuous operating mode is used.
In some embodiments, GDI source 200 is configured for pulsed operation.
Ions are generated for the duration of time 274 when bias potential 272 is applied to the electrodes. In some embodiments, the timing of the pulsed bias potential 272 during pulsed mode operation can be synchronized with modulation signal 412 used to generate high voltage RF signal 482, which is applied to the center electrode of ion trap 104, as will be discussed in more detail subsequently. Graph 280 in
Pulsed mode operation can have several advantages. For example, the repetition frequency, and the duration and/or amplitude of the pulsed bias potential 272 can be adapted to the amount of gas particles to be analyzed that are present and the gas pressure in ion trap 104. In general, controller 108 monitors the ion current measured by detector 118, and based on the magnitude of the ion current, controller 108 can adjust one or more of the parameters associated with pulsed mode operation.
In some embodiments, for example, controller 108 can adjust the amplitude of bias potential 272. Increasing the bias potential can increase the rate at which ions are produced in GDI source 200.
In certain embodiments, controller 108 can adjust the repetition frequency of bias potential 272. For some analytes of interest, increasing the repetition frequency can increase the rate at which ions are generated in GDI source 200. For other analytes, decreasing the repetition frequency can increase the rate at which ions are generated in GDI source 200. Controller 108 can be configured to adjust the repetition frequency in adaptive fashion until the rate of ion generation in GDI source 200 reaches a suitable value.
In some embodiments, controller 108 can be configured to adjust the duty cycle of GDI source 200. Referring to graph 270, the duty cycle of GDI source 200 refers to the ratio of the duration of time 274 during which bias potential 272 is applied to the total period 276. Controller 108 can be configured to adjust the duty cycle of GDI source 200. For example, the duty cycle can be reduced to reduce the rate at which ions are produced in GDI source 200. By reducing the rate at which ions are produced, the signal-to-noise ratio of the measured ion signal can be improved, and unwanted ghost peaks can be eliminated (e.g., peaks due to unwanted charged particles that are produced by GDI source 200 when measuring ions with source 200 turned off. Alternatively, the duty cycle can be increased to increase the rate at which ions are produced in GDI source 200.
In certain embodiments, controller 108 can be configured to adjust the duty to a value between 1% and 50% (e.g., between 1% and 40%, between 1% and 30%, between 1% and 20%, between 1% and 10%).
Another important advantage of pulsed mode operation is that the bias potential applied between electrodes 210 and 220 is turned off when unneeded, e.g., when source 200 has already generated ions. Turning off the bias potential during most of the duty cycle of source 200 can lead to a significant reduction in the amount of power required to operate spectrometer.
In addition, pulsed mode operation avoids the use of a gate or shield positioned between GDI source 200 and detector 118. Eliminating gates and shields, which are commonly used in conventional mass spectrometers, conserves considerable space, and further reduces the amount of power required to operate spectrometer 100.
In some embodiments, the operating condition of GDI source 200 can be checked using an automated calibration process. For example, a user can activate the calibration process where one or more known reference samples are sequentially analyzed. Detection of phantom peaks (i.e., peaks that should not exist in the measured spectra) can indicate that the GDI source 200 is contaminated. For example, either of electrodes 210 and 220 can become embedded with sticky particles or debris that may result in the detection of phantom peaks. In some calibration processes, no samples are injected, and phantom peaks are detected against a background of spectrometer noise. Determination of whether the GDI source 200 needs to be replaced can be based on the calibration results, e.g, based on the number and size of phantom peaks detected.
To facilitate replacement, in some embodiments ion source 102 can be configured as a separate module from the other components of spectrometer 100. For example, as shown in
In some embodiments, GDI source 200 can be cleaned instead of being replaced. For example, GDI source 200 can be cleaned by applying a potential bias to electrodes 210 and 220 that corresponds to an inverse duty cycle.
In some embodiments, controller 108 is configured to adjust the duty cycle during cleaning to a value between 50% and 100% (e.g., between 50% and 90%, between 50% and 80%, between 50% and 70%, between 50% and 60%). The inverse duty cycle can be applied for a total time period of 5 s or more (e.g., 10 s or more, 20 s or more, 30 s or more, 40 s or more, 50 or more, 1 minute or more, 2 minutes or more, 3 minutes or more, 5 minutes or more).
Other methods can also be used to clean the electrodes of GDI source 200 if they become contaminated. In some embodiments, cleaning gas can be injected into GDI chamber 230 to facilitate the removal of sticky particles on electrodes 210 and 220. Suitable cleaning gases can include noble gases, for example. Further, in certain embodiments, cleaning of the electrodes of GDI source 200 can also be facilitated by heating the electrodes 210 and 220. In some embodiments, electrodes 210 and 220 can be removed from GDI chamber 230 and cleansed in a suitable cleaning solution.
The foregoing discussion focused on the measurement of phantom peaks to determine whether GDI source 200 is contaminated. More generally, other methods can also be used in addition to, or as an alternative to, phantom peak detection. For example, controller 108 can be configured to monitor the measurement of ion currents by detector 118. If the ion signal measured by detector 118 flickers or suddenly changes (e.g., jumps or drops down) by more than a threshold amount, or if the average detected ion/electron signal has decays below a particular threshold value, controller 108 can determine automatically that cleaning or replacement of GDI source 200 is desirable.
A variety of materials can be used to form the electrodes in ion source 102, including electrodes 210 and 220 in GDI source 200. In certain embodiments, the electrodes of ion source 102 can be made from materials such as copper, aluminum, silver, nickel, gold, and/or stainless steel. In general, materials that are less prone to adsorption of sticky particles are advantageous, as the electrodes formed from such materials typically require less frequent cleaning or replacement.
The foregoing discussion has focused on the use of GDI source 200 in spectrometer 100. However, the features, design criteria, algorithms, and aspects described above are equally applicable to other types of ion sources that can be used in spectrometer 100, such as capacitive discharge sources and thermionic emitter sources. In particular, capacitive discharge sources are well suited for use at the relatively high gas pressures at which spectrometer 100 operates. As such, the foregoing description applies to such sources as well. For example,
Due to the use of compact, closely spaced electrodes, the overall size of ion source 102 can be small. The maximum dimension of ion source 102 refers to the maximum linear distance between any two points on the ion source. In some embodiments, the maximum dimension of ion source 102 is 8.0 cm or less (e.g., 6.0 cm or less, 5.0 cm or less, 4.0 cm or less, 3.0 cm or less, 2.0 cm or less, 1.0 cm or less).
III. Ion Trap
As explained above in Section I, ions generated by ion source 102 are trapped within ion trap 104, where they circulate under the influence of electrical fields created by applying electrical potentials to the electrodes of ion trap 104. The potentials are applied to the electrodes of ion trap 104 by voltage source 106, after receiving control signals from controller 108. To eject the circulating ions from ion trap 104 for detection, controller 108 transmits control signals to voltage source 106 which cause voltage source 106 to modulate the amplitude of a radiofrequency (RF) field within ion trap 104. Modulation of the amplitude of the RF field causes the circulating ions within ion trap 104 to fall out of orbit and exit ion trap 104, entering detector 118 where they are detected.
As explained above in Section I, to ensure that mass spectrometer 100 is both compact and consumes a relatively small amount of electrical power during operation, mass spectrometer 100 uses only a single, small mechanical pump in pressure regulation subsystem 120 to regulate its internal gas pressure. As a result, mass spectrometer 100 operates at internal gas pressures that are higher than internal pressures in conventional mass spectrometers. To ensure that gas particles drawn in to spectrometer 100 are quickly ionized and analyzed, the internal volume of mass spectrometer 100 is considerably smaller than the internal volume of conventional mass spectrometers. By reducing the internal volume of spectrometer 100, pressure regulation subsystem 120 is capable of drawing gas particles quickly into spectrometer 100. Further, by ensuring quick ionization and analysis, a user of spectrometer 100 can rapidly obtain information about a particular substance. A smaller internal volume of spectrometer 100 has the added advantage of a smaller internal surface area that is susceptible to contamination during operation. Conventional mass spectrometers use a variety of different mass analyzers, many of which have large internal volumes that are maintained at low pressure during operation, and/or consume large amounts of power during operation. For example, certain mass spectrometers use linear quadrupole mass filters, which have large internal volumes due to their extension in the axial direction, which enables mass filtering and large charge storage capacities. Some conventional mass spectrometers use magnetic sector mass filters, which are also typically large and may consume large amounts of power to generate mass-filtering magnetic fields. Conventional mass spectrometers can also use hyperbolic ion traps, which can have large internal volumes, and can also be difficult to manufacture.
In contrast to the foregoing conventional ion trap technologies, the mass spectrometers disclosed herein use compact, cylindrical ion traps for trapping and analyzing ions.
During operation, ions generated by ion source 102 enter ion trap 104 through aperture 320 in electrode 304. Voltage source 106 applies potentials to electrodes 304 and 306 to create an axial field (e.g., symmetric about axis 318) within ion trap 104. The axial field confines the ions axially between electrodes 304 and 306, ensuring that the ions do not leave ion trap through aperture 320, or through aperture 322 in electrode 306. Voltage source 106 also applies an electrical potential to central electrode 302 to generate a radial confinement field within ion trap 104. The radial field confines the ions radially within the internal aperture of electrode 302.
With both axial and radial fields present within ion trap 104, the ions circulate within the trap. The orbital geometry of each ion is determined by a number of factors, including the geometry of electrodes 302, 304, and 306, the magnitudes and signs of the potentials applied to the electrodes, and the mass-to-charge ratio of the ion. By changing the amplitude of the electrical potential applied to central electrode 302, ions of specific mass-to-charge ratios will fall out of orbit within trap 104 and exit the trap through electrode 306, entering detector 118. Therefore, to selectively analyze ions of different mass-to-charge ratios, voltage source 106 (under the control of controller 108) changes the amplitude of the electrical potential applied to electrode 302 in step-wise fashion. As the amplitude of the applied potential changes, ions of different mass-to-charge ratio are ejected from ion trap 104 and detected by detector 118.
Electrodes 302, 304, and 306 in ion trap 104 are generally formed of a conductive material such as stainless steel, aluminum, or other metals. Spacers 308 and 310 are generally formed of insulating materials such as ceramics, Teflon® (e.g., fluorinated polymer materials), rubber, or a variety of plastic materials.
The central openings in end-cap electrodes 304 and 306, in central electrode 302, and in spacers 308 and 310 can have the same diameter and/or shape, or different diameters and/or shapes. For example, in the embodiment shown in
In general, the diameter c0 of the central opening in electrode 302 can be selected as desired to achieve a particular target resolving power when selectively ejecting ions from ion trap 104, and also to control the total internal volume of spectrometer 100. In some embodiments, c0 is approximately 0.6 mm or more (e.g., 0.8 mm or more, 1.0 mm or more, 1.2 mm or more, 1.4 mm or more, 1.6 mm or more, 1.8 mm or more). The diameter c2 of the central opening in end-cap electrodes 304 and 306 can also be selected as desired to achieve a particular target resolving power when ejecting ions from ion trap 104, and to ensure adequate confinement of ions that are not being ejected. In certain embodiments, c2 is approximately 0.25 mm or more (e.g., 0.35 mm or more, 0.45 mm or more, 0.55 mm or more, 0.65 mm or more, 0.75 mm or more).
The axial length c1 of the combined openings in electrode 302 and spacers 308 and 310 can also be selected as desired to ensure adequate ion confinement and to achieve a particular target resolving power when ejecting ions from ion trap 104. In some embodiments, c1 is approximately 0.6 mm or more (e.g., 0.8 mm or more, 1.0 mm or more, 1.2 mm or more, 1.4 mm or more, 1.6 mm or more, 1.8 mm or more).
It has been determined experimentally that the resolving power of spectrometer 100 is greater when c0 and c1 are selected such that c1/c0 is greater than 0.83. Therefore, in certain embodiments, c0 and c1 are selected so that the value of c1/c0 is 0.8 or more (e.g., 0.9 or more, 1.0 or more, 1.1 or more, 1.2 or more, 1.4 or more, 1.6 or more).
Due to the relatively small size of ion trap 104, the number of ions that can simultaneously be trapped in ion trap 104 is limited by a variety of factors. One such factor is space-charge interactions among the ions. As the density of trapped ions increases, the average spacing between the trapped, circulating ions decreases. As the ions (which all have either positive or negative charges) are forced closer together, the magnitude of repulsive forces between the trapped ions increases.
To overcome limitations on the number of ions that can simultaneously be trapped in ion trap 104 and increase the capacity of spectrometer 100, in some embodiments spectrometer 100 can include an ion trap with multiple chambers.
In some embodiments, the number of ion chambers 330 in ion trap 104 can be matched to the number of apertures formed in end cap electrode 304. As described in Section II, end cap electrode 304 can, in general, include one or more apertures. When end cap electrode 304 includes a plurality of apertures, ion trap 104 can also include a plurality of ion chambers 330, so that each aperture formed in end cap electrode 304 corresponds to a different ion chamber 330. In this manner, ions generated within ion source 102 can be efficiently collected by ion trap 104, and trapped within ion chambers 330. The use of multiple chambers, as described above, reduces space-charge interactions among the trapped ions, increasing the trapping capacity of ion trap 104. In general, the positions and cross-sectional shapes of ion chambers 330 can be the same as the arrangements and shapes of apertures 240 and 294 discussed in Section II.
As an example, referring to
In certain embodiments, the number, arrangement, and/or cross-sectional shapes of ion chambers 330 are not matched to the arrangement of apertures in end cap electrode 304. For example, end cap electrode 304 can include only one or a small number of apertures 294, and ion trap 304 can nonetheless include a plurality of ion chambers 330. Because the use of multiple ion chambers 330 increases the trapping capacity of ion trap 104, using multiple ion chambers can provide advantages even if the arrangement of the ion chambers is not matched to the arrangement of apertures in end cap electrode 304.
Additional features of ion trap 104 are disclosed, for example, in U.S. Pat. No. 6,469,298, in U.S. Pat. No. 6,762,406, and in U.S. Pat. No. 6,933,498, the entire contents of each of which are incorporated herein by reference.
IV. Voltage Source
Voltage source 106 provides operating power and electrical potentials to the components of spectrometer 100 based on signals transmitted by controller 108 over control line 127e. As discussed above in Section I, important advantages of the mass spectrometers disclosed herein are their compact size and significantly reduced power consumption, relative to conventional mass spectrometers. While spectrometer 100 can generally operate with a variety of voltage sources, to reduce power consumption by spectrometer 100 as much as possible, it is advantageous if voltage source 106 is a high efficiency source.
However, high efficiency voltage sources that are both small in size, and that generate voltages sufficient to drive the components of spectrometer 100, are not readily obtained commercially.
The design of power supply 106 allows spectrometer 100 to be operated at high power efficiency throughout the various sweeping stages of the high voltage RF signal 482. At each stage, the power efficiency is defined as the ratio of the input electrical power to the output electrical power. In some embodiments, the efficiency of power supply 106 can be 40% or higher (e.g., 50% or higher, 60% or higher, 70% or higher, 80% or higher, 90% or higher) at all stages of the voltage amplification. In contrast, conventional power amplifiers (e.g., emitter followers or class-A amplifiers) typically have a maximum efficiency at the highest amplification level, but significantly reduced efficiencies at lower amplification levels. As such, conventional power amplifiers can be inefficient and unsuitable for applications requiring sweeping voltage amplifications.
In addition to high efficiency operation, voltage source 106 enables relatively low power sources (e.g., batteries) to provide the electrical power and potentials needed to activate the various components of spectrometer 100. As a result, spectrometer 100 has a compact form factor and is considerably lighter than conventional mass spectrometers.
Referring to
During operation, PID control loop 420 receives a modulation signal 412 from a modulation signal generator 410, which may or may not be a component of voltage source 106.
Switch-mode supply 430 is configured to receive input power signal 442 from power source 440, which can include a battery (e.g., a Li-ion, Li-Poly, NiCd, or NiMH battery). The voltage supplied by power source 440 is typically between about 0.5 V and about 13V. As an example, the voltage can be about 7.2V. Switch-mode supply 430 amplifies input power signal 442 based on control signal 422, resulting in a modulated voltage signal 432, which is sent to linear regulator 450 (if present). An example of modulated voltage signal 432 is shown in
In some embodiments, switch-mode supply 430 includes a switching regulator for efficient power amplification. During operation, input power signal 442 can be less than, equal to, or greater than output voltage signal 432. This feature is particularly advantageous when power source 440 is a battery. Unlike linear power supplies, switch-mode supply 430 (which is a nonlinear amplifier) can dissipate little or no power when switching between various amplification states, leading to high power conversion. In addition, switch-mode supply 430 is typically more compact and lighter conventional linear power supplies due to the smaller internal transformer size and weight.
Linear regulator 450 is optionally included in voltage source 106. If linear regulator 150 is not present in voltage source 106, then modified voltage signal 432 is directly sent from switch-mode supply 430 to class-D amplifier 460. Alternatively, when linear regulator 450 is present in voltage source 106, then linear regulator 150 receives both modulated voltage signal 432 from switch-mode supply 430, and control signal 424 from PID control loop 420.
Linear regulator 450 functions to filter irregularities in modified voltage signal 432. The filtered voltage signal 442 from linear regulator 450 is received by class-D amplifier 442. Typically, linear regulator 450 includes a low-dropout voltage regulator, where a constant low drop voltage can ensure that the overall efficiency of the voltage source 106 is only slightly lowered due to the presence of linear regulator 450. In certain embodiments, control signal 424 received by the linear regulator 450 is used to modify the envelope of the output voltage signal 442 to be suitable for measuring mass spectra for specific substances.
Reference wave generator 470 is optionally included in voltage source 106. If present, reference wave generator 470 provides a reference wave signal 472 to class-D amplifier 460. In general, reference wave signal 472 has a frequency in the radio frequency range (e.g., from about 0.1 MHz to about 50 MHz). For example, in some embodiments, reference wave signal 472 can have a frequency of 1 MHz or higher (e.g., 2 MHz or higher, 4 MHz or higher, 6 MHz or higher, 8 MHz or higher, 15 MHz or higher, 30 MHz or higher).
Class-D amplifier 460 receives both reference wave signal 472 (if reference wave generator 470 is present) and filtered voltage signal 442 (or modified voltage signal 432, if linear regulator 450 is not present) and generates a modulated RF signal 462 from these input signals.
RF signal 462 is received by resonant circuit 480, which is also shown schematically in
In some embodiments, resonant circuit 480 has a Q-factor of 60 or more (e.g., 80 or more, 100 or more). When RF signal 462 is applied to the resonant circuit 480, a high voltage RF signal 482 is generated on capacitor 488. In general, the waveform of high voltage RF signal 482 is the same as, or approximately the same as, the waveform of RF signal 462, except that the amplitude of high voltage RF signal 482 is significantly larger than the amplitude of RF signal 462. For example, in some embodiments, the maximum amplitude of high voltage RF signal 482 is 100V or higher (e.g., 500V or higher, 1000V or higher, 1500V or higher, 2000V or higher). In general, the high Q-factor of resonant circuit 480 allows for the generation of large amplitude voltages in RF signal 482.
The combination of class-D amplifier 462 and resonant circuit 480 is advantageous for a number of reasons, including low power consumption and frequency adjustment. A further important advantages arises from the fact that a pure sinusoidal reference wave signal 472 is not required for operation. Instead, the combination of class-D amplifier 462 and resonant circuit 480 can use reference wave signals with a variety of waveform shapes. Certain waveform shapes, such as square waves, can often be generated with higher fidelity than pure sinusoidal waveforms. As a result, the combination of class-D amplifier 462 and resonant circuit 480 permits operation with reference wave signals of high stability.
Returning to
The feedback signal received from resonant circuit by signal monitor 490 can be transmitted to PID control loop 420 and/or reference wave generator 470 as control signal 492. Based on control signal 492, PID control loop 420 can send modified control signals 422 and 424 to switch-mode supply 430 and linear regulator 450, respectively, to optimize the waveform and amplitude of high voltage RF signal 482. For example, PID control loop 420 can modify the envelope of modified voltage signal 432 based on control signal 492, thereby maximizing the amplitude of high voltage RF signal 482.
In some embodiments, the resonant frequency of resonant circuit 480 may not exactly match the frequency of reference wave signal 472. For example, this may occur due to inaccurate values of the inductance of inductor 486 and/or the capacitance of capacitor 488. Further, the inductance of inductor 486 and/or the capacitance of capacitor 488 can change over time. This can also occur, for example, if class-D amplifier 460 distorts the output frequency of RF signal 462, so that the frequency of RF signal 462 no longer matches the frequency of reference signal wave 472. This mismatch may potentially reduce the efficiency of voltage source 106 because resonant circuit 480 ceases to be an effective resonator for RF signal 462.
Several techniques can be implemented to compensate for this mismatch. In some embodiments, the frequency of reference wave signal 472 can be scanned by reference wave generator 470 while monitoring the control signal 492. Reference wave generator 470 can select the optimum frequency for reference wave signal 472 as the frequency that maximizes the amplitude of control signal 492.
In certain embodiments, the capacitance of capacitor 488 can be varied in resonant circuit 480, to determine which capacitance value maximizes the amplitude of control signal 492. For this purpose, capacitor 488 can be a variable capacitor.
The foregoing techniques for compensating for frequency mismatch can be implemented directly in hardware, in software, or both. For example, controller 108 can be configured to perform one or more of these methods to compensate for frequency mismatch. Controller 108 can be configured to perform these methods automatically and/or on an ongoing basis to continually optimize frequency matching. Alternatively, controller 108 can be configured to only perform these methods upon receiving an instruction from a user, e.g., when a user activates a control on user interface 112. When executed by controller 108, the techniques for compensating for frequency mismatch disclosed herein typically are complete within 5 minutes or less (e.g., 3 minutes or less, 2 minutes or less, 1 minute or less).
High voltage RF signal 482 is applied to ion trap 104 (e.g., to central electrode 302 of ion trap 104) to selectively eject trapped ions for detection by detector 118. The range of mass-to-charge ratios that can be analyzed using ion trap 104 depends upon, among other factors, the profile of RF signal 482 (e.g., the envelope and maximum amplitude). By varying these features of RF signal 482, voltage source 106 (under the control of controller 108) can select the range of mass-to-charge ratios that are analyzed.
In some embodiments, voltage source 106 can include multiple reference wave generators 470 and/or multiple resonant circuits 480. During operation, a combination of a particular reference wave generator 470 and a particular resonant circuit 480 can be selected by controller 108 to generate a suitable high voltage RF signal 482 for analyzing a particular range of mass-to-charge ratios using ion trap 104. To change the range of mass-to-charge ratios that are analyzed, controller 108 selects a different reference wave generator 470 and/or resonant circuit 480.
V. Detector
Detector 118 is configured to detect charged particles leaving ion trap 104. The charged particles can be positive ions, negative ions, electrons, or a combination of these.
A wide variety of different detectors can be used in spectrometer 100.
For example, base 502 can have a variety of cross-sectional shapes, including square, rectangular, elliptical, circular, or any other regular or irregular shape. Base 502 can be flat or curved, for example.
In general, Faraday cup 500 can relatively small. The maximum dimension of Faraday cup 500 corresponds to the largest linear distance between any two points on the cup. In some embodiments, for example, the maximum dimension of Faraday cup 500 is 30 mm or less (e.g., 20 mm or less, 10 mm or less, 5 mm or less, 3 mm or less).
Typically, the thickness of base 502 and/or the thickness of sidewall 504 are chosen to ensure efficient detection of charged particles. In some embodiments, for example, the thickness of base 502 and/or of sidewall 504 are 5 mm or less (e.g., 3 mm or less, 2 mm or less, 1 mm or less).
The sidewall 504 and base 502 of Faraday cup 500 are generally formed from one or more metals. Metals that can be used to fabricate Faraday cup 500 include, for example, copper, aluminum, and silver. In some embodiments, Faraday cup 500 can include one or more coating layers on the surfaces of base 502 and/or sidewall 504. The coating layer(s) can be formed from materials such as copper, aluminum, silver, and gold.
During operation of spectrometer 100, as charged particles are ejected from ion trap 104, the charged particles can drift or be accelerated into Faraday cup 500. Once inside Faraday cup 500, the charged particles are captured at the surface of Faraday cup 500 (e.g., the surface of base 502 and/or sidewall 504). Charged particles that are captured either by base 502 or sidewall 504 generate an electrical current, which is measured (e.g., by an electrical circuit within detector 118) and reported to controller 108. If the charged particles are ions, the measured current is an ion current, and its amplitude is proportional to the abundance of the measured ions.
To obtain a mass spectrum of an analyte, the amplitude of the electrical potential applied to central electrode 302 of ion trap 104 is varied (e.g., a variable amplitude signal, high voltage RF signal 482, is applied) to selectively eject ions of particular mass-to-charge ratios from ion trap 104. For each change in amplitude corresponding to a different mass-to-charge ratio, an ion current corresponding to ejected ions of the selected mass-to-charge ratio is measured using Faraday cup 500. The measured ion current as a function of the potential applied to electrode 302—which corresponds to the mass spectrum—is reported to controller 108, In some embodiments, controller 108 converts applied voltages to specific mass-to-charge ratios based on algorithms and/or calibration information for ion trap 104.
Following ejection from ion trap 104 through end cap electrode 306, charged particles can be accelerated to impact detector 118 by forming an electric field between the detector 118 and end cap electrode 306. In certain embodiments, where detector 118 includes Faraday cup 500 for example, the conducting surface of the Faraday cup 500 is maintained at the ground potential established by voltage source 106, and a positive potential is applied to end cap electrode 306. With these applied potentials, positive ions are repelled from end cap electrode 306 toward the grounded conducting surface of Faraday cup 500. Further, electrons passing through end cap electrode 306 are attracted toward end cap electrode 306, and thus do not impact Faraday cup 500. This configuration therefore leads to improved signal-to-noise ratio. More generally, in this configuration, Faraday cup 500 can be at a potential other than ground, as long as it is at a lower potential than end cap electrode 306.
In some embodiments, it is desirable to detect negatively charged particles (e.g., negative ions and/or electrons). To detect such particles, Faraday cup 500 is biased to a higher voltage than end cap electrode 306 to attract negatively charged particles to the Faraday cup 500.
In some embodiments, detector 118 can include a Faraday cup 500 with two regions separated by an insulating region. Different bias potentials can be applied to each region. For example,
In some embodiments, detector 118 can be directly secured to housing 122. For example,
In certain embodiments, housing 122 can be configured such that detector 118 can be easily mounted or removed. For example, as shown in
In some embodiments, Faraday cup 500 can implemented as a component of pluggable, replaceable module 148, as described in Section I. In a modular configuration, Faraday cup 500 can be formed, for example, as a recess in a plate of conducting material. The plate can be directly attached to another component of module 148, such as ion trap 104, so that the aperture in end cap electrode 306 is aligned with the recess, and ions ejected from ion trap 104 enter the Faraday cup directly. Modules with different Faraday cup dimensions can be used to provide selective detection of different types of analytes.
In some embodiments, a biased repelling grid or magnetic field can be placed in front of a Faraday cup 500 to prevent secondary charged particle emission, which may distort the measurement of ejected ions from ion trap 104. Alternatively, in certain embodiments, the secondary emission from Faraday cup 500 can be used for detection of the ejected ions.
While the preceding discussion has focused on Faraday cup detectors due to their low power operation and compact size, more generally a variety of other detectors can be used in spectrometer 100. For example, other suitable detectors include electron multipliers, photomultipliers, scintillation detectors, image current detectors, Daly detectors, phosphor-based detectors, and other detectors in which incident charged particles generate photons which are then detected (i.e., detectors that employ a charge-to-photon transduction mechanism).
VI. Pressure Regulation Subsystem
Pressure regulation subsystem 120 is generally configured to regulate the gas pressure in gas path 128, which includes the interior volumes of ion source 102, ion trap 104, and detector 118. As discussed above in Section I, during operation of spectrometer 100, pressure regulation subsystem 120 maintains a gas pressure within spectrometer 100 that is 100 mTorr or more (e.g., 200 mTorr or more, 500 mTorr or more, 700 mTorr or more, 1 Torr or more, 2 Torr or more, 5 Torr or more, 10 Torr or more), and/or 100 Torr or less (e.g., 80 Torr or less, 60 Torr or less, 50 Torr or less, 40 Torr or less, 30 Torr or less, 20 Torr or more).
In some embodiments, pressure regulation subsystem 120 maintains gas pressures within the above ranges in certain components of spectrometer 100. For example, pressure regulation subsystem 120 can maintain gas pressures of between 100 mTorr and 100 Torr (e.g., between 100 mTorr and 10 Torr, between 200 mTorr and 10 Torr, between 500 mTorr and 10 Torr, between 500 mTorr and 50 Torr, between 500 mTorr and 100 Torr) in ion source 102 and/or ion trap 104 and/or detector 118. In certain embodiments, the gas pressures in at least two of ion source 102, ion trap 104, and detector 118 are the same. In some embodiments, the gas pressure in all three components is the same.
In certain embodiments, gas pressures in at least two of ion source 102, ion trap 104, and detector 118 differ by relatively small amounts. For example, pressure regulation subsystem 120 can maintain gas pressures in at least two of ion source 102, ion trap 104, and detector 118 that differ by 100 mTorr or less (e.g., 50 mTorr or less, 40 mTorr or less, 30 mTorr or less, 20 mTorr or less, 10 mTorr or less, 5 mTorr or less, 1 mTorr or less). In some embodiments, the gas pressures in all three of ion source 102, ion trap 104, and detector 118 differ by 100 mTorr or less (e.g., 50 mTorr or less, 40 mTorr or less, 30 mTorr or less, 20 mTorr or less, 10 mTorr or less, 5 mTorr or less, 1 mTorr or less).
As shown in
The orbital motion of scroll flanges 602 and 604 allows scroll pump 600 to generate only very small amplitude vibrations and low noise during operation. As such, scroll pump 600 can be directly coupled to ion trap 104 without introducing substantial detrimental effects during mass spectrum measurements. To further reduce vibrational coupling, orbiting scroll flange 602 can be counterbalanced with simple masses. Because scroll pumps have few moving parts and generate only very small amplitude vibrations, the reliability of such pumps is generally very high.
Scroll pump 600 is typically compact in size, and has a small mass. In some embodiments, for example, the maximum dimension of scroll pump 600 (e.g., the largest linear distance between any two points on scroll pump 600) is less than 10 cm (e.g., less than 8 cm, less than 6 cm, less than 5 cm, less than 4 cm, less than 3 cm, less than 2 cm). In certain embodiments, the weight of scroll pump 600 is less than 1.0 kg (e.g., less than 0.8 kg, less than 0.7 kg, less than 0.6 kg, less than 0.5 kg, less than 0.4 kg, less than 0.3 kg, less than 0.2 kg).
The small size and weight of scroll pump 600 allows it to be incorporated into spectrometer 100 in a variety of configurations. In some embodiments, for example, as shown in
Scroll pumps suitable for use in pressure regulation subsystem 120 are available, for example, from Agilent Technologies Inc. (Santa Clara, Calif.). In addition to scroll pumps, other pumps can also be used in pressure regulation subsystem 120. Examples of suitable pumps include diaphragm pumps, diaphragm pumps, and roots blower pumps.
Using a small, single mechanical pump provides a number of advantages relative to the pumping schemes used in conventional mass spectrometers. In particular, conventional mass spectrometers typically use multiple pumps, at least one of which operates at high rotational frequency. Large mechanical pumps operating at high rotational frequencies generate mechanical vibrations that can couple into the other components of the spectrometer, generating undesirable noise in measured information. In addition, even if measures are taken to isolate the components from such vibrations, the isolation mechanisms typically increase the size of the spectrometers, sometimes considerably. Furthermore, large pumps operating at high frequencies consume large amounts of electrical power. Accordingly, conventional mass spectrometers include large power supplies for meeting these requirements, further enlarging the size of such instruments.
In contrast, a single mechanical pump such as a scroll pump can be used in the spectrometers disclosed herein to control gas pressures in each of the components of the system. By operating the mechanical pump at a relatively low rotational frequency, the mechanical coupling of vibrations into other components of the spectrometer can be substantially reduced or eliminated. Further, by operating at low rotational frequencies, the amount of power consumed by the pump is small enough that its modest requirements can be met by voltage source 106.
It has been determined experimentally that in some embodiments, by operating the single mechanical pump at a frequency of less than 6000 cycles per minute (e.g., less than 5000 cycles per minute, less than 4000 cycles per minute, less than 3000 cycles per minute, less than 2000 cycles per minute), the pump is capable of maintaining desired gas pressures within spectrometer 100, and at the same time, its power consumption requirements can be met by voltage source 106.
VII. Housing
As described above in Section I, mass spectrometer 100 includes a housing 122 that encloses the components of the spectrometer.
In some embodiments, display 116 is a passive or active liquid crystal or light emitting diode (LED) display. In certain embodiments, display 116 is a touchscreen display. Controller 108 is connected to display 116, and can display a variety of information to a user of mass spectrometer 100 using display 116. The information that is displayed can include, for example, information about an identity of one or more substances that are scanned by spectrometer 100. The information can also include a mass spectrum (e.g., measurements of abundances of ions detected by detector 118 as a function of mass-to-charge ratio). In addition, information that is displayed can include operating parameters and information for mass spectrometer 100 (e.g., measured ion currents, voltages applied to various components of mass spectrometer 100, names and/or identifiers associated with the current module 148 installed in spectrometer 100, warnings associated with substances that are identified by spectrometer 100, and defined user preferences for operation of spectrometer 100). Information such as defined user preferences and operating settings can be stored in storage unit 114 and retrieved by controller 108 for display
In some embodiments, as shown in
When display 116 is a touchscreen display, a portion, or even all, of user interface 112 can be implemented as a series of touchscreen controls on display 116. That is, some or all of the controls of user interface 112 can be represented as touch-sensitive areas of display 116 that a user can activate by contacting display 116 with a finger.
As described in Section I, in some embodiments, mass spectrometer 100 includes a replaceable, pluggable module 148 that includes ion source 102, ion trap 104, and (optionally) detector 118. When mass spectrometer 100 includes a pluggable module 148, housing 122 can include an opening to allow a user to access the interior of housing 122 to replace module 148, without disassembling housing 122.
In
In general, mass spectrometer 100 can include a variety of different sample inlets 124. For example, in some embodiments, sample inlet 124 includes an aperture configured to draw gas particles directly from the environment surrounding spectrometer 100 into gas path 128. Sample inlet 124 can include one or more filters 706. For example, in some embodiments, filter 706 is a HEPA filter, and prevents dust and other solid particles from entering spectrometer 100. In certain embodiments, filter 706 includes a molecular sieve material that traps water molecules.
As discussed previously, conventional mass spectrometers operate at low internal gas pressures. To maintain low gas pressures, conventional mass spectrometers include one or more filters attached to sample inlets. These filters are selective, and filter out particles of certain types of substances, such as atmospheric gas particles (e.g., nitrogen and/or oxygen molecules) from entering the mass spectrometer. The filters can also be specifically tailor for certain classes of analytes such as biological molecules, and can filter out other types of molecules. As a result, the filters that are used in conventional mass spectrometers—which can include pinch valves, and membrane filters formed from materials such as polydimethylsiloxane which permit selective transport of substances—filter the incoming stream of gas particles to remove certain types of particles from the stream. Without such filters, conventional mass spectrometers could not function, as the low internal gas pressure could not be maintained, and some of the particles admitted into the mass spectrometers would prevent operation of certain components. As an example, thermionic ion sources that are used in conventional mass spectrometers do not operate in the presence of even moderate concentrations of atmospheric oxygen.
The use of substance-specific filters in conventional mass spectrometers has a number of disadvantages. For example, because the filters are selective, fewer analytes can be analyzed without changing filters and/or operating conditions, which can be cumbersome. In particular, for an untrained user of a mass spectrometer, re-configuring the spectrometer for specific analytes by choosing an appropriate selective filter may be difficult. Further, the filters used in conventional mass spectrometers introduce a time delay, because analyte particles do not diffuse instantly through the filters. Depending upon the selectivity of the filters and the concentration of the analyte, a considerable delay can be introduced between the time the analyte is first encountered, and the time when sufficient quantities of analyte ions are detected to generate mass spectral information.
However, because the mass spectrometers disclosed herein operate at higher pressures, there is no need to include a filter such as a membrane filter to maintain low gas pressures within the spectrometer. By operating without the types of filters that are used in conventional mass spectrometers, the spectrometers disclosed herein can analyze a greater number of different types of samples without significant re-configuration, and can perform analyses faster. Moreover, because the components of the spectrometers disclosed herein are generally not sensitive to atmospheric gases such as nitrogen and oxygen, these gases can be admitted to the spectrometers along with particles of the analyte of interest, which significantly increases the speed of analysis and decreases the operating requirements (e.g., the pumping load on pressure regulation subsystem 120) of the other components of the spectrometers.
Accordingly, in general, the filters used in the spectrometers disclosed herein (e.g, filter 706) do not filter atmospheric gas particles (e.g., nitrogen molecules and oxygen molecules) from the stream of gas particles entering sample inlet 124. In particular, filter 706 allows at least 95% or more of the atmospheric gas particles that encounter the filter to pass through.
Different types of filters 706 can be replaceable, and can be changed by a user of spectrometer 100 if they become dirty or ineffective. In some embodiments, mass spectrometer 100 can include multiple filters 706, and a user can selectively install any one or more of the filters depending upon the nature of the sample that is being analyzed.
In certain embodiments, sample inlet 124 can be configured to receive a substance to be analyzed by direct injection. For example, filter 706 can be replaced by a sample injection port attached to sample inlet 124. During use of spectrometer 100, a substance injected into sample inlet 124 through the sample injection port is introduced into gas path 128, ionized by ion source 102, and analyzed by ion trap 104 and detector 118.
In some embodiments, spectrometer 100 can include a variety of sample introduction modules that can be attached to housing 122 to introduce different types of analytes into spectrometer 100. A sample introduction module 750 is shown schematically in
In general, various sample introduction modules can be used with spectrometer 100. For example, in some embodiments, module 750 is a vapor thermal desorption module. In certain embodiments, module 750 is a low temperature plasma module. In some embodiments, module 750 is an electrospray ionization module. Each of these modules can be used interchangeably with spectrometer 100 to analyze a wide variety of different samples.
In addition to replaceable modules 750, spectrometer 100 can also include a variety of sensors. For example, in some embodiments, mass spectrometer 100 can include a limit sensor 708 coupled to controller 108. Limit sensor 708 detects gas particles in the environment surrounding mass spectrometer, and reports gas concentrations to controller 108. During operation of mass spectrometer 100 by a user, controller 108 monitors the length of time and concentration of gases measured by limit sensor 708, and displays a warning to the user (e.g., via display 116) if the exposure of the user to gas particles exceeds a threshold concentration or threshold time limit. Information about threshold exposure concentrations and time limits can be stored in storage unit 114, for example, and retrieved by controller 108. Example limit sensors that can be used in mass spectrometer 100 include combustible/LEL gas sensors, photoionization sensors, electrochemical sensors, and temperature and humidity sensors.
In certain embodiments, mass spectrometer 100 can include an explosion hazard sensor 710. Explosion hazard sensor 710, which is connected to controller 108, detects the presence of explosive substances in the vicinity of spectrometer 100. Threshold concentrations for a variety of explosive substances can be stored in storage unit 114, and retrieved by controller 108. During operation of spectrometer 100, when concentrations of one or more explosive substances measured by sensor 710 exceed threshold values, controller 108 can display a warning message to the user of spectrometer 100 via display 116. In some embodiments, the warning message can advise the user to either stop using spectrometer 100, or to use it inside an auxiliary shield (e.g., a cage) to prevent ignition of the one or more explosive substances. Explosion hazard sensors that can be used with mass spectrometer 100 include, for example, combustible sensors, available from MSA (Cranberry Township, PA), and RAE Systems (San Jose, Calif.).
Housing 122 is generally shaped so that it can be comfortably operated by a user using either one hand or two hands. In general, housing 122 can have a wide variety of different shapes. However, due to the selection and integration of components of spectrometer 100 disclosed herein, housing 122 is generally compact. As shown in
Further, due to the selection of components within spectrometer 100, the overall weight of spectrometer 100 is significantly reduced relative to conventional mass spectrometers. In certain embodiments, for example, the total weight of spectrometer 100 is 4.5 kg or less (e.g., 4.0 kg or less, 3.0 kg or less, 2.0 kg or less, 1.5 kg or less, 1.0 kg or less, 0.5 kg or less).
VIII. Operating Modes
In general, mass spectrometer 100 operates according to a variety of different operating modes.
In some embodiments, controller 108 can initiate a scan automatically based on one or more sensor readings. For example, when spectrometer 100 includes limit sensors such as photoionization detectors and/or LEL sensors, controller 108 can monitor signals from these sensors. If the sensors indicate that a substance of potential interest has been detected, for example, controller 108 can initiate a scan. In general, a wide variety of different sensor-based events or conditions can be used by controller 108 to initiate a scan automatically.
In certain embodiments, spectrometer 100 can be configured to run in “continuous scan” mode. After spectrometer 100 has been placed in continuous scan mode, a scan is repeatedly initiated after expiration of a fixed time interval. The time interval is configurable by the user, and the value of the time interval can be stored in storage unit 114 and retrieved by controller 108. Thus, in step 802 of
After the scan has been initiated, the sample is introduced into spectrometer 100 in step 804. A variety of different methods can be used to introduce the sample into the spectrometer. In some embodiments, where the sample consists of gas particles (e.g., gas particles 822 in
In certain embodiments, the sample can be introduced into spectrometer 100 via direct injection. As disclosed above in Section VII, spectrometer 100 can include a sample injection port connected to sample inlet 124. The sample injection port allows the user of spectrometer 100 to inject the sample directly into sample inlet 124 for analysis. Once injected, the sample enters gas path 128.
In certain embodiments, a sample in a partially ionized state can be drawn into spectrometer 100 by electrostatic or electrodynamic forces. For example, by applying suitable electrical potentials to electrodes in spectrometer 100, charged particles can be accelerated into spectrometer 100 (e.g., through sample inlet 124).
Next, in step 806, the sample is ionized in ion source 102. As disclosed above, a sample inlet 124 can be positioned in different locations along gas path 128, relative to the other components of spectrometer 100. For example, in some embodiments, sample inlet 124 is positioned so that gas particles introduced into spectrometer 100 enter ion trap 104 first from sample inlet 124. In certain embodiments, sample inlet 124 is positioned so that gas particles introduced into spectrometer 100 enter ion source 102 first from sample inlet 124. In some embodiments, sample inlet 124 is positioned so that gas particles enter detector 118 first from sample inlet 124. Still further, sample inlet 124 can be positioned so that gas particles that enter spectrometer 100 enter gas path 128 at a point between ion source 102 and/or ion trap 104 and/or detector 118.
After the sample (e.g., as gas particles 822) has been introduced into spectrometer 100 at a point along gas path 128, some of the gas particles enter ion source 102. If sample inlet 124 is not positioned so that gas particles 822 enter ion source 102 directly, then movement of gas particles 822 into ion source 102 occurs by diffusion. Once inside ion source 102, controller 108 activates ion source 102 to ionize the gas particles, as disclosed in Section II.
Next, the ions generated in step 806 are trapped in ion trap 104 in step 808. As disclosed in Section II above, movement of the ions from ion source 102 to ion trap 104 generally occurs under the influence of electric fields generated between ion source 102 and ion trap 104. Once inside ion trap 104, the ions are trapped by electric fields internal to the trap, and circulate within the opening in central electrode 302, and between end cap electrodes 304 and 306. The electric fields within ion trap 104 are generated by voltage source 106 under the control of controller 108, which applies suitable electrical potentials to electrodes 302, 304, and 306 to generate the trapping fields.
In step 810, the trapped, circulating ions in ion trap 104 are selectively ejected from the trap. As disclosed above in Section III, selective ejection of ions from trap 104 occurs under the control of controller 108, which transmits signals to voltage source 106 to vary the amplitude of the applied RF voltage to the central electrode 302. As the amplitude of the potential is varied, the amplitude of the electric field in the internal opening of central electrode 302 also varies. Further, as the amplitude of the field within central electrode 302 varies, circulating ions with specific mass-to-charge ratios fall out of circulating orbit within central electrode 302, and are ejected from ion trap 104 through one or more apertures in end cap electrode 306. Controller 108 is configured to direct voltage source 106 to sweep the amplitude of the applied potential according to a defined function (e.g., a linear amplitude sweep) to selectively eject ions of specific mass-to-charge ratios from ion trap 104 into detector 118. The rate at which the applied potential is swept can be determined automatically by controller 108 (e.g., to achieve a target resolving power of spectrometer 100), and/or can be set by a user of spectrometer 100.
After the ions have been selectively ejected from ion trap 104, they are detected by detector 118 in step 812. As disclosed in Section V, a variety of different detectors can be used to detect the ions. For example, in some embodiments, detector 118 includes a Faraday cup that is used to detect the ejected ions.
For each mass-to-charge ratio selected by the amplitude of the electrical potential applied to central electrode 302 in ion trap 104, detector 118 measures a current related to the abundance of ions detected with the selected mass-to-charge ratio. The measured currents are transmitted to controller 108. As a result, the information that controller 108 receives from detector 118 corresponds to detected abundances of ions as a function of mass-to-charge ratio for the ions. This information corresponds to a mass spectrum of the sample.
More generally, controller 108 is configured to detect ions according to a mass-to-charge ratio for the ions, which means that controller 108 detects or receives signals that correlate with the detection of ions and are related to the mass-to-charge ratio for the ions. In some embodiments, controller 108 detects ions or receives information about ions directly as a function of mass-to-charge ratio. In certain embodiments, controller 108 detects ions or receives information about ions as a function of another quantity, such as an electrical potential applied to ion trap 104, that is related to the mass-to-charge ratio for the ions. In all such embodiments, controller 108 detects ions according to a mass-to-charge ratio.
In step 814, the information received from detector 118 is analyzed by controller 108. In general, to analyze the information, controller 108 (e.g., electronic processor 110 in controller 108) compares the mass spectrum of the sample to reference information to determine whether the mass spectrum of the sample is indicative of any of the known substances. The reference information can be stored, for example, in storage unit 114, and retrieved by controller 108 to perform the analysis. In some embodiments, controller 108 can also retrieve reference information from databases that are stored at remote locations. For example, controller 108 can communicate with such databases using communication interface 117 to obtain mass spectra of known substances, for use in analyzing the information measured by detector 118.
The information measured by detector 118 is analyzed by controller 108 to determine information about an identity of the sample. If the sample includes multiple compounds, controller 108—by comparing the measured information from detector 118 to reference information—can determine information about the identities of some or all of the multiple compounds.
Controller 108 is configured to determine a variety of information about the identity of a sample. For example, in some embodiments, the information includes one or more of the sample's common name, IUPAC name, CAS number, UN number, and/or its chemical formula. In certain embodiments, the information about the identity of the sample includes information about whether the sample belongs to a certain class of substances (e.g., explosives, high energy materials, fuels, oxidizers, strong acids or bases, toxic agents). In some embodiments, the information can include information about hazards associated with the sample, handling instructions, safety warnings, and reporting instructions. In certain embodiments, the information can include information about a concentration or level of the sample measured by the spectrometer.
In certain embodiments, the information can include an indication as to whether or not the sample corresponds to a target substance. For example, when a scan is initiated in step 802, a user of spectrometer 100 can place the spectrometer in targeting mode, in which spectrometer 100 scans samples to specifically determine whether a sample corresponds to any of a series of identified target substances. Controller 108 can use a variety of data analysis techniques such as digital filtering and expert systems to search for particular spectral features in the measured mass spectral information. For a particular target substance, controller 108 can search for particular mass spectral features that are characteristic for the target substance, such as peaks at particular mass-to-charge ratios. If certain spectral features are missing from the measured mass spectral information, or if the measured information includes spectral features where none should appear, the information about the identity of the sample determined by controller 108 can include an indication that the sample does not correspond to the target substance. Controller 108 can be configured to determine such information for multiple target compounds.
After the sample analysis is complete, controller 108 displays information about the sample to the user in step 816, using display 116. The information that is displayed depends upon the operating mode of spectrometer 100 and the actions of the user. As disclosed in Section I, spectrometer 100 is configured so that it can be used by persons who do not have special training in the interpretation of mass spectra. For persons without such training, complete mass spectra (e.g., ion abundances as a function of mass-to-charge ratio) often carry little meaning. As a result, spectrometer 100 is configured so that in step 816, it does not display the measured mass spectrum of the sample to the user. Instead, spectrometer 100 displays only some (or all) of the information about the identity of the sample, as determined in step 814, to the user. For users without special training, information about the identity of the sample is of primary significance.
In addition to the information about the identity of the sample, controller 108 can also display other information. For example, in some embodiments, spectrometer 100 can access a database (e.g., stored in storage unit 114, or accessible via communication interface 117) of known hazardous materials. If the information about the identity of the sample is present in the database of hazardous materials, controller 108 can display alerting messages and/or additional information to the user. The alerting messages can include, for example, information about the relative hazardousness of the sample. The additional information can include, for example, actions that the user should consider taking, including actions to limit exposure of the user or others to the substance, and other security-related actions.
In some embodiments, spectrometer 100 is configured to display the mass spectrum of the sample to the user when a control is activated. Referring to
In some embodiments, control 824 can be configured to allow two different modes of operation. For example, when control 824 is activated to a first state by a user of spectrometer 100, information about the identity of the sample is displayed to the user on display 116 when the analysis is completed. When control 824 is activated to a second state, the mass spectral information (e.g., ion abundances as a function of mass-to-charge ratio) is displayed. Thus, control 824 can have the form of a two-way switch that permits the user to select a desired information display mode during operation of the spectrometer. In certain embodiments, when control 824 is activated to the second state, spectrometer 100 can also be configured to display information about the identity of the sample, in addition to the mass spectral information.
In step 818, the process shown in flow chart 800 terminates. If the scan was initiated in step 802 by the user activating control 820, then spectrometer 100 waits for control 820 to be activated again before initiating another scan. Alternatively, if spectrometer 100 is in continuous scan mode, then spectrometer 100 waits for a defined time interval, and then initiates another scan automatically after the interval has elapsed, or waits for another external trigger such as a sensor signal.
As discussed previously, in general, spectrometer 100 does not use a filter that filters atmospheric gas particles. As a result, when particles of an analyte are introduced into the spectrometer, atmospheric gas particles are also introduced, forming a mixture of gas particles in spectrometer 100. Because spectrometer 100 operates at pressures that are substantially higher than the internal pressures in conventional mass spectrometers, and because the components of spectrometer 100 are generally relatively insensitive to atmospheric gas particles, the spectrometers disclosed herein can be used to introduce analytes in ways that are not possible with conventional mass spectrometers. In particular, particles of an analyte can be introduced by continuously drawing in a mixture of particles of the analyte and atmospheric gas particles, without filtering any of the particles. In some embodiments, spectrometer 100 can be configured to continuously introduce a mixture of gas particles into gas path 128 through sample inlet 124 for a period of at least 10 s (e.g., at least 15 s, at least 20 s, at least 30 s, at least 45 s, at least 1 minute, at least 1.5 minutes, at least 2 minutes, at least 3 minutes, at least 4 minutes, at least 5 minutes) or more.
When particles of an analyte are continuously introduced for an extended duration of time, spectrometer 100 can also adjust the duty cycle of ion source 102 so that ion source 102 generates ions for an extended period of time (e.g., a portion of, or the entire, period during which analyte particles are introduced). As explained previously, the duty cycle of ion source 102 can generally be adjusted (e.g., by adjusting time duration 274 in
As discussed above, spectrometer 100 achieves both compactness and low power operation by eliminating certain high power-consumption components that are typically found in conventional mass spectrometers. Among these components, vacuum pumps—in particular, turbomolecular pumps—are both heavy, and consume large quantities of power. Spectrometer 100 does not include such pumps, and as a result, is both significantly lighter, and consumes significantly less power, than conventional mass spectrometers.
Using pressure regulation subsystem 120, spectrometer 100 operates at internal gas pressures that are significantly higher than the internal gas pressures of conventional mass spectrometers. In general, at higher pressures, the resolution of a mass spectrometer is degraded due to a variety of mechanisms, including collision-induced line broadening and ion-neutral charge exchange. Thus, to obtain the highest possible resolution mass spectra, the internal gas pressure in a mass spectrometer should be maintained as low as possible.
However, as explained above, useful information about a sample, including information about the identity of the sample, can be obtained and provided to a user by measuring the sample's mass spectrum when the mass spectrometer's resolution is worse than the best possible value. In particular, sufficiently precise correspondences between measured mass spectral information and reference information can be achieved even when mass spectrometer 100 operates at a higher internal gas pressure—and therefore a poorer resolution—than conventional mass spectrometers.
Because mass spectrometer 100 operates at lower resolution than a conventional mass spectrometer, mass spectrometer 100 can be further configured, in some embodiments, to adaptively adjust the operation of certain components to further reduce its overall power consumption. Components are adaptively operated either to achieve a target resolution in the measured mass spectral information, or to achieve a sufficient correspondence between the mass spectral information and reference information on a known substance or condition.
Then, in step 858, sample ions generated by ion source 102 are detected using detector 118. Step 858 can be performed without activating ion trap 104 to trap or selectively eject ions. Instead, in step 858, ions generated by ion source 102 pass directly through end cap electrodes 304 and 306 of ion trap 104, and are incident on detector 118. Voltage source 106 can be configured to apply electrical potentials to electrodes in ion source 102 and detector 118 to create an electric field between ion source 102 and detector 118 to promote the transport of ions.
Next, in step 860, controller 108 determines whether a threshold ion current has been detected by detector 118. The threshold ion current can be a user-defined and/or user-adjustable setting of spectrometer 100. Alternatively, the threshold ion current can be determined automatically by spectrometer 100 based on, for example, a measurement of dark current and/or noise in detector 118 by controller 108. If the threshold current has not yet been reached, ionization of the sample and detection of sample ions continues in steps 856 and 858. Alternatively, if the threshold ion current has been reached, controller 108 activates ion trap 104 in step 862 to trap and selectively eject ions into detector 118. The ejected ions are detected by detector 118, and the mass spectral information is analyzed by controller 108 in step 864 in an attempt to determine information about an identity of the sample.
As part of the analysis in step 864, controller 108 can determine a probability that the measured mass spectral information for the sample originates from a known substance or condition. In step 866, controller 108 compares the determined probability to a threshold probability to determine whether the analysis of the mass spectral information is limited by the resolution of spectrometer 100. If the probability is larger than the threshold value, then controller 108 displays information about the sample (e.g., an identity of the sample and/or information about an identity of the sample) using display 116, and the process concludes at step 870. However, if the probability is less than the threshold probability value in step 866, then the analysis of the mass spectral information may be limited by the resolution of spectrometer 100.
In some embodiments, step 866 includes determining whether a probability of correct detection is sufficiently large (e.g., exceeds a threshold probability value). The probability of correct detection corresponds to a probability that the mass spectral information correctly matches spectral information for a known substance. Such probabilities can be calculated in a variety of ways, including for example by using correspondences between the observed and known fragmentation patterns of target analytes, using abstract features of the observed measurements known to be predictive of analyte presence, using decision trees based on the measured conditions and observed fragmentation patterns from the unknown materials, and using dynamic properties of the unknown samples such its response to positive and negative ionization, or axial excitation. If the probability of correct detection is too low, controller 108 adjusts the configuration of the spectrometer in step 872.
In certain embodiments, step 866 includes determining whether a probability of a false alarm is sufficiently low (e.g., is smaller than a threshold probability value). The probability of a false alarm corresponds to a probability that the measured spectral information corresponds to known spectral information for one or more substances that are hazardous and/or targeted for detection by spectrometer 100 and/or a user of the spectrometer. The probability of a false alarm can be calculated, for example, from the degree of confusion in the algorithms, or the vagueness of the posterior probability distributions. If the probability of a false alarm is sufficiently low (e.g., smaller than the threshold value), then spectrometer 100 continues to step 868. Alternatively, if the probability of a false alarm exceeds the threshold value, controller 108 adjusts the configuration of the spectrometer in step 872.
To increase the enhance the resolution of spectrometer 100, controller 108 adaptively adjusts the configuration of the spectrometer, before control returns to step 862. Controller 108 is configured to adjust the configuration in a variety of ways to increase the resolution of spectrometer 100. In some embodiments, controller 108 is configured to activate buffer gas source 150 to introduce buffer gas particles into gas path 128. The introduced buffer gas particles can include, for example, nitrogen molecules, hydrogen molecules, or atoms of a noble gas such as helium, argon, neon, or krypton. Buffer gas source 150 can include a replaceable cylinder containing the buffer gas particles, and a valve connected to controller 108 via control line 127g, or a buffer gas generator. Controller 108 can be configured to activate the valve in buffer gas source 150 so that controlled quantities of buffer gas particles are released into gas path 128. Once released into gas path 128, the buffer gas particles mix with the ions generated by ion source 102, and facilitate trapping and selective ejection of the ions into detector 118, thereby increasing the resolving power of spectrometer 100.
In certain embodiments, controller 108 reduces the internal gas pressure in spectrometer 100 to increase the resolving power of spectrometer 100. To reduce the internal gas pressure, controller 108 activates pressure regulation subsystem 120 via control line 127d. Alternatively, or in addition, controller 108 can close valve 129 to reduce the internal gas pressure. In some embodiments, valve 129 can be alternately opened and closed in pulsed fashion with a particular duty cycle to reduce the internal gas pressure. In certain embodiments, spectrometer 100 can include multiple sample inlets, and valve 129 can be closed to seal sample inlet 124, while another in-line valve in a smaller diameter sample inlet can be opened. By using a different sample inlet to reduce the gas pressure in spectrometer 100, no change in pumping speed is necessary. Reducing the internal gas pressure in spectrometer 100 increases the resolution of spectrometer 100 by reducing the frequency of collisions between ions in ion source 102, ion trap 104, and detector 118.
In some embodiments, to improve the resolution of spectrometer 100, controller 108 increases the frequency at which the electrical potential applied to center electrode 302 changes. By decreasing the rate at which the applied potential changes, the rate at which the internal electric field within electrode 302 changes is also decreased. As a result, the selectivity with which ions are ejected from ion trap 104 increases, improving the resolution of spectrometer 100.
In certain embodiments, controller 108 is configured to change the axial electric field frequency or amplitude within ion trap 104 to change the resolution of spectrometer 100. Changing the axial electric field in ion trap 104 can shift the ejection boundary of the ion trap, thereby either extending or reducing the high-mass range of the spectrometer and modifying the resolving power and/or resolution of spectrometer 100.
In some embodiments, controller 108 is configured to increase the resolution of spectrometer 100 by changing a duty cycle of ion source 102. Reducing the ionization time has been observed experimentally to improve resolution in mass spectrometer 100. Thus, referring to graph 270 in
Conversely, reducing the resolution of spectrometer 100 can also be useful in certain situations. For example, referring to graphs 270 and 280 in
In certain embodiments, controller 108 is configured to increase the resolution of spectrometer 100 by increasing the duration of time over which the electrical potential applied to electrode 302 of ion trap 104 is increased (e.g., interval 286 in
In some embodiments, controller 108 is configured to change the resolution of spectrometer 100 by adjusting the ramp profile associated with the amplitude sweep of the potential applied to electrode 302. As shown in graph 280 of
As discussed above, controller 108 is configured to take any one or more of the above actions to change the resolution of spectrometer 100. The order in which these actions are taken can either be determined by spectrometer 100, or by user preferences. For example, in some embodiments, a user of spectrometer 100 can designate which of the above steps, and in which order, controller 108 takes to increase the resolution and/or reduce the power consumption of spectrometer 100. The user selections can be stored as a set of preferences in storage unit 114. Alternatively, in some embodiments, the order of actions taken by controller 108 can be permanently encoded into the logic circuitry of controller 108, or stored as non-modifiable settings in storage unit 114.
In certain embodiments, controller 108 can determine an order of actions based on other considerations. For example, to ensure that spectrometer 100 consumes as little electrical power as possible, the order of actions taken by controller 108 to improve the resolving power of spectrometer 100 can be determined according to increase in power consumption as a result of each action. Controller 108 can be configured with information about how each of the actions disclosed above increases overall power consumption, and can select an appropriate order of actions based on the power consumption information, with actions that cause the smallest increases in power consumption occurring first. Alternatively, controller 108 can be configured to measure the increase in power consumption associated with each of the actions, and can select an appropriate order of actions based on the measured power consumption values.
Although in flow chart 850 adjustments to the configuration of spectrometer 100 are based on the probability that the measured mass spectral information corresponds to known reference information, adjustments to the configuration of spectrometer 100 can also be made based on other criteria. In some embodiments, for example, adjustments to the configuration of spectrometer 100 can be made based on whether or not a target resolution of spectrometer 100 has been achieved. In step 864, controller 108 determines the actual resolution of spectrometer 100 based on the measured mass spectral information (e.g., based on the largest FWHM of a single ion peak within the measurement window of spectrometer 100). In step 866, the actual resolution is compared by controller 108 to a target resolution for spectrometer 100. If the actual resolution is less than the target resolution, then in step 872, controller 108 adjusts the configuration of spectrometer 100, as discussed above, to improve the resolution of the spectrometer.
IX. Adaptive Analysis of Samples
The methods shown in flow chart 850 of
More sophisticated methods for adaptively analyzing samples can also be implemented in spectrometer 100. In some embodiments, more sophisticated methods can employ a system operational framework that includes a combination of computational algorithms for signal conditioning, methods for adaptive hardware control, and situational classification and detection algorithms. These features work together to yield a system that operates with high sensitivity and selectivity, and at the same time is highly efficient as well.
A variety of general techniques can be used in such methods to achieve enhanced performance. For example, signal processing and conditioning methods can be used to improve the signal-to-noise ratio of measured signals (e.g., measured mass spectral information) and also of signals measured by a variety of on-board sensors (e.g., pressure sensors, temperature sensors, voltage sensors, current sensors, power sensors). Such methods can be used to provide feedback-based control of hardware components of spectrometer 100, e.g., adjusting a spectral acquisition rate by selecting the rate at which voltage source 106 sweeps the amplitude of the potential applied to trap 104 to selectively eject ions of specific mass-to-charge ratios from ion trap 104 into detector 118. By using signal processing and conditioning methods, spectrometer 100 can be used to analyze a wide variety of samples in many different environments (e.g., with varying noise levels from different sources), maintaining a level of performance that meets or exceeds desired performance criteria.
Dynamic hardware management methods can be used to ensure that spectrometer 100 is neither overloaded nor under-loaded with sample material. Such methods can include adjustment of various properties of ion source 102 to control the quantity of ions produced from a sample and injected into ion trap 104. Controlling the quantity of ions produced ensures that phenomena such as space-charge and collision-induced effects do not adversely affect the spectral resolution of spectrometer 100.
A variety of different classification techniques can be implemented at various stages within the overall analysis scheme to allow spectrometer 100 to further adapt its operation to the specific conditions that exist when analyzing a particular sample. For example, in some embodiments, an intermediate situational classification technique can by implemented to identify, at a relatively high level of generality, the type of sample present and/or the general environment of the analyzer. This information can be used to adjust operating parameters of spectrometer 100 so that the hardware components of the spectrometer operate in an efficient and highly sensitive configuration for detection of the type of sample or environment that is present.
In certain embodiments, preliminary target detection methods can be used to narrow down the identity of the sample from a large number of possibilities to a list of a few candidates with highest probability. These target detection methods can incorporate a model of noise signals within spectrometer 100 so that the methods remain robust even within a variety of environmental and operating conditions. The information derived from target detection methods can then be used in highly selective confirmatory detection techniques to provide a more conclusive identification of the sample.
By using some or all of the foregoing techniques, spectrometer 100 can operate at a high level of efficiency (e.g., reduced power consumption), and at the same time, can provide highly sensitive and selective detection for a wide range of different analytes. The combination of high sensitivity and selectivity and efficient operation is achieved because the operating parameters of spectrometer 100 are specifically adjusted for the detection of the sample at hand, and because analysis of the measured spectral information is adapted to ensure that significant computational resources of spectrometer 100 are not wasted by analyzing the spectral information in a manner that will not lead to identification. Accordingly, efficient operation of spectrometer 100 also leads to rapid identification of many different analytes.
In the first step 902 which occurs after a sample has been introduced into spectrometer 100 (using any of the methods described above), spectrometer 100 performs an ionization mode survey to determine which mode provides the most efficient analysis for the sample. Typically, spectrometer 100 alternates between four different ionization modes: a low mass positive ionization mode, a low mass negative ionization mode, a high mass positive ionization mode, and a high mass negative ionization mode. Switching between positive and negative ionization is used to determine which ionization mode produces the largest number of ions from the sample. Switching between low mass and high mass detection is used to determine the expected range of masses for the ions produced from the sample, so that the detection range of spectrometer 100 can be adapted to the expected mass range. This survey is performed extremely rapidly, typically in 500 ms or less (e.g., in 200 ms or less, in 150 ms or less, in 100 ms or less, in 80 ms or less, in 60 ms or less, in 50 ms or less), and in some embodiments, on the order of 50-100 ms.
Typically, the ionization mode survey is performed at high operating pressure. For example, during step 902, the gas pressure within ion source 102 and/or ion trap 106 and/or detector 118 is 0.5 Torr or more (e.g., 1 Torr or more, 2 Torr or more, 3 Torr or more, 5 Torr or more, 10 Torr or more). Further, ion source 102 operates with a relatively long ionization time and a short cooling time. In certain embodiments, for example, the ionization time is between 2 ms and 40 ms The relatively long ionization time implies that a duty cycle of ion source 102 during the ionization mode survey is relatively large. In some embodiments, for example, the duty cycle is 50% or more.
During the ionization mode survey, ion trap 104 is operated with a short trapping time. The short trapping time (i.e., the period of time during which ions generated from the sample remain within the trap before being ejected into detector 118), combined with the large duty cycle of ion source 102, favors sensitivity and speed of detection at the expense of selectivity. Thus, by operating ion source 102 and ion trap 104 in this manner, highly sensitive detection of ions occurs in spectrometer 100, but the ability of spectrometer 100 to resolve small differences in mass-to-charge ratios is lowered. For purposes of performing an ionization mode survey, however, this compromise is acceptable, as the objective is to determine which ionization mode yields the largest ion current, not to perform a highly selective analysis of the ions that are generated. In general, the trapping time of the ions within trap 104, which corresponds to the time interval over which the trapping voltage is swept between its maximum and minimum values, is 2 ms or less (e.g., 1 ms or less, 0.5 ms or less, 0.2 ms or less).
In some embodiments, during the ionization mode survey, ion trap 104 is operated such that ions are not trapped at all. For example, controller 108 can apply no electrical potentials to ion trap 104 so that electrons generated by ion source 102 merely pass through ion trap 104. This mode of operation causes detector 118 to operate in a manner similar to an electron capture detector. The ion current measured by detector 118 in such a configuration, which depends in part on the electron capture by analyte molecules along the path from ion source 102 to detector 118, provides a quantitative indicator of analyte present in the sample by ion source 102. By cycling through the different ionization modes as described above, the mode that produces the largest number of ions from the sample can be determined. For example, with a pulse glow-discharge source set up to predominantly act as an electron source, a significant drop in ion current at the detector suggests the presence of an electronegative analyte in the analyzer (e.g., halogenated organics, or nitro-aromatics).
In general, the ionization mode survey is performed within a relatively short period of time. For example, in some embodiments, the survey is performed within 1 second or less (e.g., 0.5 seconds or less, 0.2 seconds or less, 0.1 seconds or less, 0.08 seconds or less, 0.06 seconds or less, 0.04 seconds or less, 0.02 seconds or less). Typically, spectrometer 100 is operated in each of the four different ionization modes for approximately one quarter of the total survey time. Thus, spectrometer 100 can operate in each ionization mode for 0.25 seconds or less (e.g., 0.2 seconds or less, 0.15 seconds or less, 0.1 seconds or less, 0.08 seconds or less). More generally, however, spectrometer 100 can be operated in each of the different ionization modes for different periods of time; the amount of time during which spectrometer 100 operates in any of the modes can be adjusted, e.g., via user-selectable preferences.
In some embodiments the analysis of positive and negative ions occurs simultaneously. Since electrodynamic ion traps are charge agnostic (i.e., positive and negative charges are trapped by the same DC/RF potentials), an ionizer capable of producing simultaneous positive and negative ions from analytes and interferences (e.g., some positive ions by electron bombardment and some negative ions by electron attachment) can result in the ion trap trapping simultaneously positive and negative ions, and simultaneously ejecting positive and negative ions as the RF potential applied to the ion trap is ramped. If two or more detectors of opposite polarity are positioned at the exit of the ion trap, the positive ions can be detected by a negatively charged detector and negative ions detected by a positively charged detector. This simultaneous positive and negative collection more than doubles the efficiency of the mass spectrometer since polarity switching is avoided, and duty cycle is effectively doubled.
In some embodiments, the ionization mode survey can be repeated for multiple cycles during step 902. For example, after cycling through each of the four ionization modes, the same cycle can be repeated once more, or several more times. If the survey is repeated, the total elapsed time for step 902 is approximately a multiple of the survey time disclosed above. For example, if the survey is repeated n times, the total elapsed time can be approximately an n-fold multiple of the survey time.
In certain embodiments, if the ionization mode survey is repeated, subsequent repetitions can exclude certain ionization modes from the survey. For example, if the first cycle of the survey yielded relatively strong ion signals from both the low mass and high mass positive ionization modes, but weak or non-existent signals from the negative ionization modes, subsequent repetitions of the ionization mode survey can include operating spectrometer 100 only in the positive ionization modes. Similar considerations apply for any of the different ionization modes that are surveyed. In addition, subsequent repetitions of the ionization mode survey can further omit certain ionization modes if the measured ion signals are sufficiently small relative to stronger ion signals from other modes.
During the ionization mode survey, ion source 102 is switched between positive and negative ionization modes by changing polarities of the driving voltages applied to the electrodes of the ion source. GDI source 200 disclosed above can be operated in positive and negative ionization modes by changing the polarities of voltages that are applied to front electrode 210 and back electrode 220. For example, by applying a negative voltage to electrode 210 and a positive voltage to electrode 220, negative ions are produced at electrode 210 and accelerated toward electrode 220. By instead applying a positive voltage to electrode 210 and a negative voltage to electrode 220, positive ions are produced at electrode 210 and accelerated toward electrode 220.
In addition to changing the polarities of the applied voltages, the magnitudes of the applied voltages can also be adjusted to control the ionization modes. As an example, the magnitude of the voltage applied to back electrode 220, which is close to ion trap 104, can be adjusted to accelerate or decelerate electrodes toward ion trap 104. A higher positive voltage applied to electrode 220 will accelerate electrons as they enter ion trap 104, where they bombard molecules in the trap. Because they have been accelerated, the electrons have higher energies, and are therefore more likely to fragment the molecules they encounter into positively charged fragments (i.e., positive ions).
Alternatively, by applying a smaller positive voltage to back electrode 220, electrons are decelerated as they approach electrode 220 and have lower energies. Lower energy electrons are more likely to promote electron attachment to molecules, favoring the generation of negative ions. If a negative voltage is applied to back electrode 220, electrons are prevented from reaching ion trap 104 through electrode 220, and positive ions only are accelerated into the ion trap.
To implement positive and negative modes of operation, detector 118 can also be switched to selectively detect either positive or negative ions. For example, for Faraday cup detector 500 disclosed above, a positive voltage bias applied to the detector will ensure that negatively charged ions are drawn to the detector and counted, while a negative voltage bias will ensure than positively charged ions are drawn to the detector and counted.
In some embodiments, detector 118 can include multiple detecting elements, such as multiple Faraday cups. The multiple detecting elements can operate in tandem to measure similarly charged particles by applying voltage biases of the same polarity to each of the multiple elements. Alternatively, the multiple detecting elements measure differently charged particles by applying voltage biases of different polarity to the elements. For example, a first electrical potential can be applied to a first subset of the detecting elements, and a second (e.g., different) electrical potential can be applied to a second subset of the detecting elements.
When different potentials are applied to different subsets of the detecting elements, the potentials can be applied at different times, or at the same time. For example, during a first portion of the survey time period discussed above, a first electrical potential can be applied to a first subset of multiple detecting elements, and during a second portion of the survey time period (e.g., different from the first portion), a second electrical potential can be applied to a second subset of the detecting elements. During these different portions of the survey time period, the system can operate in different ionization modes. For example, during the first portion of the survey time period, the system can operate in an ionization mode that generates positive ions, and the first subset of the detecting elements detects positively charged ions. During the second portion of the survey time period, the system can operate in an ionization mode that generates negative ions, and the second subset of the detecting elements detects negatively charged ions.
Alternatively, in some embodiments, electrical potentials (e.g., different electrical potentials) are applied to the first and second subsets of the detection elements at the same time, so that during at least a portion of the survey time period, the first subset of detection elements detects positively charged ions, and the second subset of detection elements detects negatively charged ions at the same time.
Where the system operates in more than two ionization modes during the survey time period, suitable electrical potentials can be applied to subsets of the detecting elements to detect ions generated during operation in each of the ionization modes. For example, when the system operates in four ionization modes, two of which generate predominantly positively charged ions and two of which generate predominantly negatively charged ions, a first electrical potential can be applied to a first subset of detection elements so that the first subset of detection elements detects positively charged ions. To detect negatively charged ions, a second electrical potential (e.g., opposite in polarity to the first potential) can be applied to a second subset of detection elements. In certain embodiments, the first and second potentials are applied at different times during the survey period (e.g., the first potential can be applied when the system is operating in the first and/or third ionization modes, and the second potential can be applied when the system is operating in the second and/or fourth ionization modes). Alternatively, in some embodiments, the first and second potentials are applied to the first and second subsets of detection elements, respectively, at the same time to enable simultaneous detection of positively and negatively charged ions.
A variety of different detectors 118 can be used to detect charged particles. As discussed above, in some embodiments, detector 118 can include one or more Faraday cups. In certain embodiments, detector 118 can include one or more glow discharge electrodes to detect charged particles generated by ion source 102.
To alternate between high and low mass ranges for the different ionization modes, the electronics coupled to ion trap 104 can include one or more RF drivers. Typically, if a single RF driver is present, the driver supplies a wide range of RF amplitudes to ion trap 104 to selectively eject different masses. In some embodiments, for example, the RF amplitudes range from approximately 100 V to approximately 20,000 V. In some embodiments, ion trap 104 includes multiple RF drivers (e.g., 2 or more RF drivers, 3 or more RF drivers, 4 or more RF drivers), each of which supplies a smaller range of RF driving voltages and phases to ion trap 104. Because each driver supplies a smaller range of voltages, the efficiency of each driver is significantly higher than the efficiency of a single driver with a wider dynamic amplitude range.
In general, the order in which the different ionization modes alternate in step 902 can be selected as desired. In some embodiments, one of the switching operations (e.g., switching between positive and negative ionization modes, and switching between low mass and high mass detection ranges) may be slower and/or may consume more power, so that the order in which the ionization modes alternate can be selected to optimize the mode switching speed and/or reduce the amount of power consumed when cycling through the different modes. For example, in certain embodiments, switching between positive and negative bias voltages applied to detector 118 can be accompanied by a delay in the voltage amplification electronics. To reduce the effect of this delay during the ionization mode survey, spectrometer 100 can be switched between positive and negative ionization modes only once, while the spectrometer is switched between low mass and high mass detection ranges twice to implement each of the four ionization modes.
During each of the ionization modes, detector 118 measures an ion current that is related to the quantity of ions that were generated from the sample and detected while spectrometer 100 was operating in that ionization mode. By comparing the signals from each of the four modes, spectrometer 100 determines which of the ionization modes is preferred for the sample (e.g., the mode that generates the ion current of largest magnitude). In addition, by measuring the magnitude of the signals, spectrometer 100 can determine information about the concentration of ions generated. The information can be used in the next step of flow chart 900.
In step 904, spectrometer 100 adjusts its operating range to account for the concentration of ions generated from the sample. Adjusting the operating range is important to ensure that the ion current generated from the sample does not saturate detector 118 or ion trap 104, which would lead to inaccurate measurement results. Each of the different detectors 118 that can be used in spectrometer 100 has an associated saturation ion current, beyond which the detector no longer reliably detects additional ions. In step 904, spectrometer 100 compares the ion current from the preferred ionization mode determined in step 902 to the saturation current for detector 118. If the ion current is larger than a threshold value relative to the saturation current (e.g., 90% of the saturation current), spectrometer 100 adjusts ion source 102 to reduce the ion current.
Alternatively, in step 904, spectrometer 100 compares the ion currents from the preferred ionization mode determined in step 902 for different electrical potentials applied to electrodes 210 and/or 220 of ion source 102. If the change in measured ion currents as a function of the applied voltage bias is nonlinear, spectrometer adjusts ion source 102 to reduce the ion current, until the measured ion currents vary in linear fashion as a function of the voltage bias applied to the electrodes of ion source 102.
In general, spectrometer 100 adjusts the ionization time in ion source 102 to reduce the ion current. Reducing the ionization time has the effect of reducing the duty cycle of ion source 102. In some embodiments, for example, the duty cycle of ion source 102 is reduced to 5% or less (e.g., 4% or less, 3% or less, 2% or less, 1% or less). The ionization time can be reduced to 100 μs or less (e.g., 90 μs or less, 80 μs or less, 70 μs or less, 60 μs or less, 50 μs or less, 30 μs or less, 10 μs or less, 5 μs or less).
In some embodiments, where the measured ion current in the preferred ionization mode is relatively small, spectrometer 100 can adjust ion source 102 to increase the ion current. Criteria for determining whether the ion current is sufficiently small can include, for example, comparison of the background current of detector 118 in a given operating condition to a threshold value (e.g., where the background current is less than 10% of the saturation current, less than 5% of the saturation current, less than 2% of the saturation current). To increase the ion current, the ionization time of ion source 102 can be increased and/or the potentials across the glow discharge source can be increased, either of which generally leads to an increase in the duty cycle of ion source 102.
After the operating range of spectrometer 100 has been adjusted, mass spectral information for the sample is acquired at moderate resolution in step 906. Typically, the resolution of the measurement performed in step 906 is greater than in step 902, but not as high as the resolution of measurements performed in subsequent steps. The mass spectral information in step 906 is generally acquired at relatively high pressures, e.g., pressures similar to those in step 902. However, to increase the resolution of the mass spectral information relative to step 902, the time over which the voltage ramp is applied to the electrodes of ion trap 104 can be increased. For example, in some embodiments, the trapping and ramp time within ion trap 104 is between 1 ms and 2 ms, whereas in a higher resolution mode of operation the ramp time may be slowed to between 4 ms and 30 ms.
In general, the moderate resolution mass spectral measurements in step 906 are performed using the preferred ionization mode determined in step 902. In some embodiments, where more than one ionization mode in step 902 yields a relatively strong ion current, the moderate resolution mass spectral measurements in step 906 can be performed using each of these ionization modes, yielding different sets of mass spectral information. For example, in certain embodiments, moderate resolution mass spectral information can be acquired using two or more, three or more, or even all four of the ionization modes from step 902. The different sets of mass spectral information can then be used to identify particular features of the sample's environment.
In step 908, spectrometer 100 performs a sample environment classification to determine information about the environment of the sample. In this step, the objective is generally not to identify the sample, but instead to identify what else is present with the sample within spectrometer 100. The other species that are present with the sample are referred to collectively as “the environment” of the sample, and can include chemical substances that accompany the sample, matrix materials in which the sample is embedded, and a variety of different contaminants and other species that may have been accidentally or unavoidably introduced into spectrometer 100. The sample environment classification identifies these potentially interfering conditions so that spectrometer 100 can compensate by adjusting its hardware configuration and/or data processing algorithms.
Interfering conditions are identified by spectrometer 100 based on the moderate resolution sets of spectral information measured in step 906. Different types of interfering species typically contribute different types of signals to the measured spectral information. Spectrometer 100 recognizes these signals in the spectral information, thereby identifying the interfering condition. Certain species can be identified based on their contributions to a single set of measured spectral information (e.g., measured spectral information from a single ionization mode). Other species are identified by spectrometer 100 based on their (changing) contributions to spectral information in different ionization modes.
In some embodiments, interfering conditions can be identified based on non-spectral information in addition to, or as an alternative to, spectral information. For example, interfering conditions can be identified based on information such as the current drawn by ion source 102, changes (e.g., reductions) in the electron flux from ion source 102, and changes in environmental conditions within spectrometer such as humidity. As an example, in some embodiments, interfering conditions can be identified based upon an estimate of total electron capture. A substantial amount of electron capture suggests a highly electronegative sample matrix, e.g., containing halogenated or nitrated organic compounds. Such compounds are more efficiently ionized and detected in negative ionization modes (e.g., by generating and detecting negative ions).
As another example, interfering aliphatic hydrocarbon species are typically strongly ionized in positive ionization modes, and are weakly ionized (or not ionized at all) in negative ionization modes. Spectrometer 100 can identify such hydrocarbon species by detecting the presence of signal contributions in spectral information from high mass and/or low mass positive ionization modes, and the absence of corresponding signal contributions in spectral information from high mass and/or low mass negative ionization modes.
In some embodiments, interfering species can be identified based on characteristic mass spectral fragmentation patterns. Such fragmentation patterns can occur at different ranges of mass to charge ratios. For example, aliphatic hydrocarbons have a characteristic mass spectral fragmentation pattern that is readily identifiable; once identified, the fragmentation pattern provides a reliable indication that interfering aliphatic hydrocarbon species are present. Pattern classification algorithms—which operate only on the measured spectral information—can be used to identify fragment patterns. For example, classification techniques such as multivariate discriminant analysis, Bayesian classifiers, support vector machines, and/or decision trees can be used to identify fragmentation patterns of common mass to charge ratio that are distinctive for aliphatic hydrocarbons.
In addition to identifying specific interfering species and/or specific classes of interfering species (e.g., hydrocarbons), spectrometer 100 can also identifying specific sample collection environments based on patterns in the different sets of measured spectral information. Spectrometer 100, due to its portability and robust operation, can be used to detect samples in a wide variety of environments. Many such environments, such as waste-contaminated sites, shipyards, and environments with petroleum-based pollutants, contain similar interfering species from one site to the next. For example, many shipyards and on-ship locations contain background concentrations of diesel fuels, ammonia, water, oil-based cleaners, and other hydrocarbons that can interfere with sample measurements.
Typical interfering species that are routinely associated with a specific sample collection environment generate reproducible sets of signals in measured mass spectral information. Spectrometer 100 can be configured to recognize these sets of signals, and based on the signals, identify the general environment in which the sample was collected. Information about the environment can then be used to adapt the spectrometer 100 configuration to compensate for interfering species which are typically present in the identified environment.
As an example, where spectrometer 100 determines that high concentrations of interfering hydrocarbon species are present—such as might be common on a marine (navy) vessel emitting diesel exhaust or in proximity to aviation vessels emitting the same—the electrical potentials applied to the electrodes of ion source 102 are adjusted so that ion source 102 operates in a negative ionization mode. For many hydrocarbon species, generation of negative ions is thermodynamically unfavorable. Thus, by operating ion source 102 in a negative ionization mode, ionization of the interfering hydrocarbon species can be significantly reduced, and even eliminated. The electrical potentials applied to detector 118 can also be adjusted so that detector 118 detects only negatively charged ions, which further reduces interference from the hydrocarbon species that are present in the sample.
In some embodiments, the operation of ion trap 104 is adjusted in addition to, or as an alternative to, adjustments to ion source 102 and/or detector 118. For example, the electrical potentials applied to electrodes of ion trap 104 can be adjusted to enhance trapping selectivity for ions of target species, while reducing trapping of ions derived from interfering species (that would otherwise compete for trapping volume within ion trap 104). As an example a combination of DC and RF potentials can be applied to the ion trap ring electrode such that a narrow mass range of fragments is trapped and subsequently ejected, eliminating interfering ions from the subsequent analysis.
Ion trap 104 can also be adjusted to control the rate of fragmentation of ions within the trap. For example, by adjusting the axial electrical potential difference between the end electrodes of ion trap 104, the extent of fragmentation within the trap can be increased (for higher potential differences, which impart greater kinetic energy to trapped ions) or decreased (for lower potential differences, which impart less kinetic energy). As an example, if the classification in step 908 indicates that significant “spectral clutter” is present due to high concentrations of interfering species, the axis electrical potential difference can be reduced (or even set to zero) to reduce collision rates within ion trap 104. As a result, the trapped ions correspond predominantly to parent ions, protonated/deprotonated parent ions, dimers, and trimmers. Analysis of mass spectral information for such a mixture of ions typically provides a more reliable identification of different species of interest present in the sample.
In some embodiments, spectrometer 100 can also identify specific classes of mass spectral information corresponding to particular samples. For example, based on the mass spectral information measured in step 908, spectrometer 100 can determine that the sample has a mass spectrum that is relatively sparse. This information can be used to configure spectrometer 100 to operate in a mode that favors acquisition of sparse mass spectral information. For example, since a sparse mass spectrum suggests a relatively clean environment free from significant concentrations of interfering species, the electron energy within ion source 102 can be increased (by applying a suitable potential to back electrode 220, for example) to increase the fragmentation of the analytes, providing additional selectivity in the measured spectral information.
Alternatively or in addition, in certain embodiments, an axial RF excitation waveform can be applied between the end electrodes of ion trap 104 to increase the kinetic energy of the trapped ions. Increasing the kinetic energy of the ions within ion trap 104 encourages greater fragmentation, providing additional selectivity.
Conversely, when the mass spectral information measured in step 908 does not suggest a a sparse mass spectrum (e.g., the spectral information is heavily cluttered as multiple fragments are detected), spectrometer 100 can reduce the electron energy within ion source 102 to reduce fragmentation of the ions trapped within ion trap 104. By reducing fragmentation, the trapped ions are predominantly parent ions, which are then ejected and detected. Fragmentation within ion source 104 can also be reduced by decreasing the magnitude of the axial RF excitation waveform applied between the end electrodes of ion trap 104.
In some embodiments, spectrometer 100 can also use information measured by additional sensors to identify interfering species and/or the collection environment of the sample. For example, spectrometer 100 can include electrochemical sensors (which are sensitive to broad classes of compounds), humidity sensors, temperature sensors, chemical sensors such as catalytic bead lower-explosive-limit (LEL) sensors, ion mobility spectrometers, photoionization detectors (PIDs), and/or surface acoustic wave sensors. Signals measured by these sensors can be used by spectrometer 100 to determine information about interfering species and/or the sample environment. In addition to signals that indicate the presence of interfering species, the absence of signals from these sensors (e.g., indicating that certain species are not present) also provides information that can be used by spectrometer 100.
Following the sample environment classification, the spectrometer operating mode is adjusted in step 910. In general, adjustment of the operating mode is performed to compensate for, or eliminate, some or all of the effects of the interfering species and/or sample collection environments identified in step 908. Alternatively, or in addition, adjustment of the operating mode is performed to favor acquisition of a certain class of mass spectral information, when it has been determined that the sample corresponds to such a class in step 908.
A wide variety of different adjustments can be performed in step 910. In some embodiments, for example, the ionization mode is adjusted from a positive mode to a negative mode or vice versa to avoid ionizing interfering species within spectrometer 100. For example, when interfering hydrocarbon species are present, ion source 102 can be configured for a negative ionization mode by applying suitable potentials to the electrodes of the ion source, provided that the sample generates a suitably large ion current in a negative ionization mode. Because hydrocarbons are typically not ionized (or weakly ionized) under such conditions, the contributions of hydrocarbon species to the measured mass spectral information can be significantly reduced.
In some embodiments, the range of mass-to-charge ratios detected by spectrometer 100 can be adjusted to exclude ranges that correspond to interfering species. For example, when ions corresponding to the sample and to interfering species have well separated mass-to-charge ratios, the trapping voltages within ion trap 104 can be selectively adjusted (e.g., by adjusting the voltage ramp applied to the electrodes of ion trap 104) to exclude mass-to-charge ranges that correspond to interfering species from the measured spectral information.
In some embodiments a chemical dopant can be introduced based on the classification in step 908. Dopants are widely used in ion mobility and mass spectrometry to increase sensitivity for selected materials and/or reduce sensitivity toward interfering species. Examples of dopants that can be introduced include, but are not limited to, methylene chloride, toluene, ammonia, and acetone.
Following adjustment of the operating mode in step 910, mass spectral information for the sample is measured in the adjusted operating mode in step 912. Because the operating mode of spectrometer 100 has been adjusted to reduce the effects of interfering species and/or favor measurement of the class of the mass spectral information corresponding to the sample, the mass spectral information obtained in step 912 typically has a higher signal-to-noise ratio than the information obtained in step 906.
Next, in step 914, spectrometer 100 performs a target detection classification using the mass spectral information acquired in step 912 to determine if the sample contains one or more known materials of interest. That is, the target detection classification in step 914 identifies a relatively small number (e.g., 10 or less, 5 or less, 3 or less, 2 or less) of candidates as possible matches for the identity of the sample.
Various methods can be used to implement target detection classification. In some embodiments, for example, the measured spectral information can be processed using a series of multivariate matched target detection filters. Such detectors are mathematical constructs specific to particular compounds. They analyze the spectral information to identify patterns therein that correspond to the compound to which they are specific, and generate a numeric value representing the likelihood that the sample contains the compound to which they are specific. As such, the target detectors typically have high sensitivity.
Absent information about the nature of the sample, the measured spectral information from step 912 can be analyzed by a large number of multivariate matched target detection filters to identify possible matches. In some embodiments, however, information derived from measurements at various points in flow chart 900 can be used to select a subset of multivariate matched target detection filters for analysis. For example, if spectrometer 100 determines in step 908 that the sample was collected in a particular environment, a set of multivariate matched target detection filters for substances commonly found in that environment can be selected by spectrometer 100 and used to process the measured spectral information.
In some embodiments, multiple analysis cycles can be performed with target detectors. For example, an initial analysis of the spectral information can be performed with a first set of target detectors to identify possible materials within the sample. If spectrometer 100 determines that additional analysis is desirable, a second set of multivariate matched target detection filters can be used to analyze the spectral information; similar additional analyses can also be performed. Spectrometer 100 can employ various criteria to determine whether additional analysis is desirable. For example, in some embodiments, spectrometer 100 can determine whether additional analysis is desirable based on the number of probabilities returned by the target detectors that exceed a particular threshold value. In certain embodiments, spectrometer 100 can determine whether additional analysis is desirable based on the maximum probability value returned by the target detectors, relative to a threshold value.
Suitable target detectors and detection techniques are disclosed, for example, in Feudale et al., “An inverse model for target detection,” Chemometrics and Intelligent Laboratory Systems 77(1-2): 75-84 (2005), and in Patcha et al., “An overview of anomaly detection techniques: Existing solutions and latest technological trends,” Computer Networks 51(12): 3448-3470 (2007), the entire contents of each of which are incorporated by reference herein.
After a set of possible matches for the identity of the sample is determined in step 914, the operating mode of spectrometer 100 is adjusted in step 916 and high resolution mass spectral information is measured. The adjustments to the operating mode in step 916 are specifically performed so that spectrometer 100 can reliably distinguish among the different possible matches identified in step 914 based on the high resolution information acquired in step 916. As such, the adjustments are not necessarily performed to yield the largest measurable ion currents or the lowest signal-to-noise ratios, but are instead performed to highlight spectral features that differentiate among the possible matches. Accordingly, in choosing which features to adjust, spectrometer 100 accounts for the different possible matches and their probabilities from step 914, and information about interfering species and/or the collection environment of the sample from step 908.
A variety of different adjustments to the operating mode of spectrometer 100 can be performed to acquire the high resolution mass spectral information. In some embodiments, for example, the trapping time within ion trap 104 (i.e., the time window over which the voltage ramp is applied to the electrodes of ion trap 104) can be increased to increase the spectral separation between different mass-to-charge ratios in the measured information. Increasing the spectral separation can reveal fine structure in the spectral information that can be used to distinguish among the possible matches for the sample.
In certain embodiments, the pressure within ion trap 104 can be reduced. Reducing the pressure within ion trap 104 reduces collisions between ions, molecules, and electrons within the trap, and improves the resolution of the mass spectral information that is measured. As an example, in some embodiments, the pressure within ion trap 104 is reduced to less than 1 Torr (e.g., less than 500 mTorr, less than 400 mTorr, less than 300 mTorr, less than 200 mTorr, less than 100 mTorr).
In some embodiments, a small quantity of a bath or buffer gas can be introduced into ion trap 104. Gases such as helium or hydrogen, when introduced, reduce the kinetic energy of ions in ion traps, thereby reducing fragmentation and improving the resolution of the measured mass spectral information. For example, the partial pressure of the bath or buffer gas in ion trap 104 can be 20% or more (e.g., 30% or more, 40% or more, 50% or more) of the total gas pressure in ion trap 104.
In certain embodiments, the drive RF frequency of ion trap 104 can be increased. By increasing the drive RF frequency, the ions are trapped for a shorter period of time within ion trap 104 prior to ejection, reducing the number of collisions among them. As a result, the resolution of the measured mass spectral information is improved. As an example, the drive RF frequency can be increased to 30 MHz or more (e.g., 40 MHz or more, 50 MHz or more, 70 MHz or more, 100 MHz or more, 150 MHz or more).
After the high resolution spectral information is acquired in step 916, sample identification is performed by spectrometer 100 in step 918. Various classification techniques can be used to identify the sample based on the high resolution spectral information. For example, in some embodiments, spectrometer 100 implements a statistical decision tree that analyzes the spectral information using a top-down, hierarchical method to arrive at an identification of the sample. In certain embodiments, Bayesian “mixture of experts” algorithms can be used to incorporate the information from the multiple stages of analysis into a final identification of the sample. Alternatively, in some embodiments, only spectral information measured at step 916 is used to identify materials of interest based on the correspondence between the observed mass spectral fragments and known fragment positions based on prior analysis of reference standards.
Suitable classification techniques are disclosed, for example, in Masoudnia, “Mixture of experts: a literature survey,” Artificial Intelligence Review, May 2012, and in Dietterich, “Ensemble Methods in Machine Learning,” in Lecture Notes in Computer Science, Vol. 1857 (Springer), 2000, pp. 1-15, the entire contents of each of which are incorporated by reference herein.
In some embodiments, step 918 does not result in a specific identification of the sample, but instead yields information about a class of compounds to which the sample belongs. For example, the classification performed by spectrometer 100 can determine that the sample corresponds to a pharmaceutical compound, to an energetic or explosive material, to a chemical weapons agent, or to another such class of materials.
After step 918 is complete, information can be delivered to a user of spectrometer 100 in step 920. The information can include the identity of the sample, whether it is believed to contain a threat material or not, the class of compounds to which the sample belongs, a variety of warning messages and/or alerts, handling information, and the other types of information disclosed previously herein. The analysis procedure then terminates at step 922.
As discussed above, spectrometer 100 can implement analysis methods that use all of the steps in flow chart 900 (even in addition to other steps), or methods that use only some of the steps shown. For example, in some embodiments, analysis methods implemented by spectrometer 100 do not include an ionization mode survey as in step 902. In certain embodiments, spectrometer 100 obtains information about interfering species from an array of auxiliary sensors, and the analysis methods implemented by spectrometer 100 do not include step 906. The method illustrated in flow chart 900 is sufficiently flexible so that various steps can be optionally performed to yield rapid, highly accurate analyses of samples while at the same time reducing power consumption by the components of spectrometer 100, by adaptively adjusting both the hardware configuration of spectrometer 100 and the analysis methodology.
Hardware, Software, and Electronic Processing
Any of the method steps, features, and/or attributes disclosed herein can be executed by controller 108 (e.g., electronic processor 110 of controller 108) and/or one or more additional electronic processors (such as computers or preprogrammed integrated circuits) executing programs based on standard programming techniques. Such programs are designed to execute on programmable computing apparatus or specifically designed integrated circuits, each comprising a processor, a data storage system (including memory and/or storage elements), at least one input device, and at least one output device, such as a display or printer. The program code is applied to input data to perform functions and generate output information which is applied to one or more output devices. Each such computer program can be implemented in a high-level procedural or object-oriented programming language, or an assembly or machine language. Furthermore, the language can be a compiled or interpreted language. Each such computer program can be stored on a computer readable storage medium (e.g., CD-ROM or magnetic diskette) that, when read by a computer, can cause the processor in the computer to perform the analysis and control functions described herein.
In some embodiments, spectrometer 100 is configured to operate at even higher gas pressures, e.g., at pressures up to 1 atm (e.g., 760 Torr). That is, the internal gas pressure in one or more of ion source 102, ion trap 104, and/or detector 118 is between 100 Torr and 760 Torr (e.g., 200 Torr or more, 300 Torr or more, 400 Torr or more, 500 Torr or more, 600 Torr or more) when spectrometer 100 is detecting ions according to a mass-to-charge ratio for the ions.
Certain components disclosed herein are already well suited to operation at pressures of up to 1 atm (and even higher pressures). For example, some of the ion sources disclosed herein, such as glow discharge ion sources, can operate at pressures up to 1 atm with little or no modification. In addition, certain types of detectors such as Faraday detectors (e.g., Faraday cup detectors and arrays thereof) can also operate at pressures of up to 1 atm with little or no modification.
The ion traps disclosed herein can be modified for operation at pressures of up to 1 atm. For example, referring to
A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.
This invention was made with Government support under Contract No. 2009*0674524*000 awarded by the Central Intelligence Agency. The Government has certain rights in the invention.
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