Patent Application
20120312980
The disclosure relates to Direct Sample Analysis systems that include ion sources that operate at atmospheric pressure and are interfaced to a mass spectrometer or other gas phase detectors. The ion sources can generate ions from multiple samples having widely diverse properties, the samples being introduced directly into the Direct Sample Analysis system ion sources.
There has been a rapid growth in recent years in the prevalence and variety of techniques for the desorption and ionization of sample species from solid surfaces at ambient atmospheric conditions, without significant sample preparation, followed by chemical analysis by mass spectrometry. Examples of such techniques include, but are not limited to: “desorption electrospray ionization” (DESI); “thermal desorption atmospheric pressure chemical ionization” (TD/APCI); “direct analysis in real time” (DART); “desorption atmospheric pressure chemical ionization” (DAPCI); and “laser desorption/electrospray ionization” (LD/ESI). Recent reviews that enumerate and elucidate such techniques are provided by: Van Berkel GJ, et. al., “Established and emerging atmospheric pressure surface sampling/ionization techniques for mass spectrometry”, J. Mass Spectrom. 2008, 43, 1161-1180; and, Venter A., et al., “Ambient desorption ionization mass spectrometry”, Trends in Analytical Chemistry, 2008, 27, 284-290.
Most such techniques have been demonstrated with ion source configurations that were open to the environment. Open configurations are attractive because they can allow easy optimization of analysis conditions, such as sample positioning and reagent source positioning, easy sample treatment during analysis, such as heating or cooling, and a straightforward exchange of samples. However, open ion source configurations may exhibit serious deficiencies with respect to safety concerns which preclude their use in unregulated facilities, and are inadvisable elsewhere for the same reasons. For example, open source configurations may not provide adequate protection for the operator from accidental exposure to the high voltages and/or elevated temperatures typically employed in such sources. Open sources may also fail to contain vaporized sample and reagent material which is often very toxic.
Apart from such safety concerns, ion sources operating at atmospheric pressure often rely on chemical reactions involving gaseous species that are present naturally in the local ambient, such as water vapor, oxygen, and/or nitrogen. As such, the performance of such sources may vary significantly as the local concentration of such reactants drifts uncontrollably, resulting in degraded performance and/or poor reproducibility. There is a significant need for a direct sample analysis system that provides real-time monitoring, feedback, conditioning and control of sample background and ionization conditions.
To date, only a few attempts are known to have been made to configure such atmospheric pressure ion sources with an enclosure that provides for safe operation, and the ability to better control and manipulate the ambient environment. However, such attempts to outfit ambient atmosphere ion sources with an enclosure have at the same time compromised some of the more advantageous features of open ion sources, such as: the ability to readily optimize the position of samples, as well as the positions of various desorption and/or ionization components, for maximum ionization efficiency and transport of ions into vacuum during operation; to readily access a sample surface, for example, to monitor the surface temperature, or to visualize the surface appearance; and the ability to configure mechanisms that allow multiple samples to be loaded into a source at the same time; and, hence, to provide for the possibility of automated operation. Therefore, there has been a need for ambient pressure ion sources that are configured with an enclosure that provides operator protection and ambient environment control, while also providing for these advantageous features otherwise available with open ambient ion sources.
Additionally, prior ambient atmosphere ion sources have been configured to accommodate only a single type of solid, liquid, or gaseous samples. Hence, there is a need for an ambient atmosphere ion source that is able to accommodate one or more samples of one or more sample types in a relatively compact space, without requiring substantial reconfiguration or operator intervention. Furthermore, there has been a need for enclosed ambient atmosphere ion sources that provide automated identification and automated optimization of the position, and orientation of samples and auxiliary components, such as desorption and/or ionization probes.
The disclosure relates to embodiments of Direct Sample Analysis (DSA) systems that include sample ionization means that operates at atmospheric pressure and allows the direct introduction of a single sample or multiple samples. These samples may vary in homogeneity and states of matter including but not limited to gas, liquid, solid, emulsions, and mixed phases. The DSA ion source system is interfaced to a mass spectrometer or other gas phase detectors, such as an ion mobility analyzer, that analyzes the mass-to-charge or mobility of ions produced in the ion source from sample species. The DSA ion source system is configured to generate sample related ions from samples introduced directly into the DSA ion source system enclosure at or near atmospheric pressure. In some embodiments, the ion source includes at least a subset of the following elements:
1. a means to load and hold single or multiple samples, for example, a sample holder assembly having removable grid sample holders,
2. a means to move and position each sample to optimize analysis of each single or multiple sample, for example, a multi-axis (e.g., four axis) translator assembly having one or more linear and rotational degrees of freedom, or various linkage or gear assemblies,
3. a means to introduce one or more gas, liquid or solid or variable property samples automatically while minimizing introduction of contamination into the ion source,
4. a means to sense the type, size, physical features and position of each sample introduced, for example, a position sensor,
5. a means to automatically identify sample holder types, for example, laser distance sensors,
6. a means to monitor and eliminate unwanted background or contamination species, for example, a countercurrent gas flow, a mass spectrometer,
7. a means to dry or condition the sample surface prior to analysis, for example, a heat source,
8. a means to heat the sample to dry and/or form sample related gas phase molecules, for example, a light source,
9. a means for sensing the temperature of the sample surface, for example, pyrometers and thermocouples,
10. a means to generate reagent ions, electrons, excited state neutral molecules (metastable species) or charged droplets to facilitate ionization of sample-related molecules, for example, a glow charge,
11. an angled reagent ion generator that enables the introduction and analysis of multiple samples positioned on a variety of sample holder types and shapes without mechanical or heat interference,
12. an angled reagent ion generator that includes a rotating exit end with exchangeable exit channels to maximize sample ionization and ion sampling efficiency,
13. a reagent ion generator that includes multiple gas inlets a liquid inlet with pneumatic nebulization of introduced liquid,
14. a means to manually or automatically position the reagent ion or electrospray charged droplet generation means to provide optimal performance, for example, position sensors used in conjunction with translator assemblies,
15. a means to direct sample related ions generated at atmospheric pressure into a mass spectrometer operating in vacuum for mass-to-charge analysis, for example, voltages applied to electrodes and ion optics,
16. an enclosure surrounding the ion source and loaded sample holder that isolates the ionization region and loaded sample from the ambient environment outside the enclosure,
17. a means to automatically control the sample holder, sensing, movement, purging, ionization and mass spectrometric or ion mobility analysis of sample related ions while the DSA system enclosure is sealed, for example, control software that include automated tuning algorithms,
18. other embodiments that generate sample related ions based on one or more of electrospray, atmospheric pressure chemical ionization (APCI), photoionization and laser ionization methods, and
19. a moisture sensor to measure the moisture content in the purge gas.
In some embodiments, the Direct Sample Analysis ion source simultaneously includes means to introduce one or more gas samples or one or more solid or liquid samples. For example, these means include one or more gas inlets and liquid inlets. Gas samples can be ionized directly in a corona discharge region or through charge exchange with gas phase reagent ions. Solid or liquid samples introduced into the ion source are evaporated and ionized through charge exchange with corona discharge generated reagent ions; charge exchange or ionization through collisions with electrospray generated ions or charged droplets; or with photoionization. In addition, sample solution can be introduced directly into the reagent ion generator where the solution is nebulized, vaporized and ionized as it passes through the corona discharge region.
The means to hold single or multiple solid, liquid or multiphase samples includes sample holders of different shapes and configurations to accommodate variations in shape, type, compositions and size of sample analyzed. The sample holder is positioned on an automated translation stage that moves the sample holder into and through ion source enclosure. In some embodiments, the sample holder translator includes a four axis motion controller with two axes of rotation and two linear motion axes. Round shaft seals are provided for three axes of motion, providing an efficient but low friction seal between the ion source interior and the ambient environment outside the ion source. One linear motion axis is fully contained within the ion source enclosure, eliminating the need for a linear seal from the external environment. The sample translator assembly within the ion source enclosure includes materials that are chemically inert and do not produce chemical contamination that can contribute unwanted chemical noise or interference ions in acquired mass spectra.
In some embodiments, the sample translator is configured to enable loading and unloading of solid or liquid phase samples through a door that is sealed when closed and minimizes the introduction of ambient contamination when open. Sequencing of clean purging gas flow through the ion source sealed enclosure minimizes the introduction of ambient contamination when loading and unloading sample holders. The gas purging also helps to reduce cross contamination between sequential samples when generating ions in the sealed enclosure. When loading and unloading solid and liquid samples the purge gas is controlled to minimize exposure to the user of samples volatilized inside the sealed ion source enclosure. The purging of background contamination species process can be monitored directly using the mass spectrometer or with additional sensors such as a moisture sensor at the outlet vent of the purge gas. In this manner of monitoring, with data dependent feedback to the control system, optimal and reproducible conditions for analysis can be achieved after loading samples, drying samples or between sample analysis to avoid carryover from sample to sample.
The disclosure includes systems having one or more position sensors to determine zero positions of the sample translator, the number of samples loaded, the shape and size of each sample and the position of each sample surface from which ions are to be generated. The zero position sensors are configured to establish the home or zero position of each axis of sample translation. In some embodiments, laser distance sensors, for example, interferometers, are configured to identify the holder type and map the sample holder surface contour, so that, once samples are loaded, a determination may be made as to which sample positions are filled, the size of each loaded sample and the position of each sample surface. Information provided by the distance sensors is processed by the software and electronics control system to enable optimal placement of each sample for maximum ion generation and mass spectrometer sampling efficiency, avoid collisions between the samples with any surface in the ion source enclosure (particularly for large or irregularly shaped samples), locate or move the reagent ion generator to its optimal position and determine the most efficient motion sequences of the sample holders for multiple sample analysis.
Precise translational control of the sample position provides a number of advantages when using both position sensing and mass spectrometric or ion mobility signal response to feedback and optimize. Using both the exact position of the surface and mass spectrometric or ion mobility signal response allows the acquisition of more uniform and accurate analytical results; particularly for samples having widely varying sizes, surface shapes, topography and properties, such as melting point. Optimum ionization and ion collection geometries can be obtained that are independent of sample-to-sample size and surface variations. In addition, nonhomogeneous sample surfaces can be positionally manipulated to analyze specific surface features. Surface analysis can be conducted with good spatial resolution by heating the surface with focused light or lasers beams. Video sensing of the surface topography can also be implemented to chemically interrogate surface features (e.g. spots on tablets).
For many liquid or solid samples, heat is required to vaporize the sample for gas phase ionization. Gas samples may also require heat to prevent sample condensation. Embodiments include means for generating heat in several different ways, including: delivering heated gas though the reagent ion generator; heating the counter current drying gas; heating using infrared, white or laser light sources; and direct sample heating through the sample holder. The total enthalpy delivered is controlled through gas heater temperature and gas flow, light or laser intensity, direct heater wattage or combinations of multiple heat sources. Enthalpy is a measure of the total energy of a system. In some embodiments, the ion source includes a means to measure the temperature of samples to provide feedback temperature control. Such feedback improves the uniformity and reproducibility of sample ionization. Examples of means to measure the temperature of samples include temperature sensors such as thermocouples and pyrometers. Thermocouples provide direct temperature feedback for gases and samples in contact with thermocouple sensors. Pyrometer sensors configured in the ion source measure temperature of a solid or liquid sample surfaces from which evaporating sample molecules are released. Precise temperature measurement and feedback control enables step-wise conditioning of the sample during analysis by applying serial thermal processes including temperature ramps, drying (unbound water), dehydrating (bound water), analyte evaporation, which is subsequently ionized, and ultimately, stages of pyrolysis or thermal decomposition that may provide structural information about the sample.
The disclosure describes multiple means to generate reagent species for ionizing sample molecules via metastable ionization, electron transfer, charge exchange or ion-molecule reactions. Examples of these means include glow discharges. Due to the sealed ion source enclosure during sample analysis, the background gas composition can be controlled to provide optimal ionization conditions. In particular, the amount of water vapor in the ion source enclosure can be controlled to efficiently generate protonated water while minimizing protonated water clusters. The disclosure features apparatus having multiple gas inlets and a liquid inlet with nebulization in the reagent ion generator. Single or multiple combinations of liquid or gas phase species can be introduced and ionized in the heated reagent ion generator. The reagent ion generator heater vaporizes nebulized liquids and some or all vapor and gas pass through a corona discharge region positioned near the reagent ion generator exit end. The corona discharge is positioned inside the reagent ion generator, which minimizes distortion of electric fields applied to direct sample ions into the mass spectrometer. Sample solution can be directly introduced into the reagent ion generator for nebulization, evaporation and ionization through Atmospheric Pressure Chemical Ionization (APCI) charge exchange reactions. In some embodiments, the vaporized liquid sample passes directly through the corona discharge region for maximum ionization efficiency.
In one example application, water can be completely removed from the ionization region and samples with lower proton affinity than water can be analyzed. Chemical ionization reagents such as methane or ammonia can be introduced to provide higher degrees of selectivity when compared to traditional APCI sources. A wide variety of reagent chemistries can be implemented with this DSA ion source system.
In some embodiments, the reagent ion generator, and in some applications the APCI sample ion generator, has an angled geometry. In some embodiments, the axis of the nebulizer and vaporizer is configured at an angle to the axis of the generator exit channel. The apparatus can include an angled exit channel configured to rotate at least 180°, which enables optimal positioning of the reagent ion generator body and exit channel, thereby maximizing analytical performance while minimizing interference with multiple sample holders. The exit channel is removable to allow the installation of optimized exit channel geometries for various sample types. The angled geometry allows the optimization of the position and angle of the reagent ion generator exit relative to sample types and relative to the mass spectrometer inlet orifice, while preventing the body of the reagent ion generator from interfering with samples and the sample holder. The angled geometry also moves the reagent ion generator heater away from the sample holder to avoid preheating of samples prior to ionization, thereby minimizing, cross-contamination between samples. In some embodiments, the reagent ion generator is positioned entirely within the Direct Analysis Source, which avoids the need for any seals in the enclosure wall except for those seals required for gas and liquid flow lines. The reagent ion generator includes materials that minimize contributions to background chemical noise in acquired mass spectra.
Depending on the sample type and geometry, the reagent ion generator exit plane and axis requires position adjustment to maximize ionization efficiency and ion transport into the mass spectrometer. In some embodiments, the reagent ion generator is mounted to a four axis translation assembly to allow a wide range of position adjustment within the DSA source enclosure. The reagent ion generator position can be set manually or automatically with position sensor feedback to the DSA source control software and electronics. In some embodiments, the reagent ion generator position can be set automatically by software and electronics, based on the distance sensor profiling of the sample holder type and sample types introduced into the ion source enclosure. Different diameter and geometry size exit sections can be exchanged on the reagent ion generator to maximize ionization efficiency for different sample types, size and species. The reagent ion generator is configured with a replaceable corona discharge needle assembly. Removal of the angled exit end facilitates removal and installation of the corona or glow discharge needle assembly.
A portion of the sample ions generated by different methods in the ion source chamber are directed toward the entrance orifice into vacuum and subsequently into the mass spectrometer where they are mass to charge analyzed. Alternatively, ions generated in the DSA source are directed into a mobility analyzer. In some embodiments of the DSA source, electric fields are applied to one or more electrodes to direct ions through an orifice into vacuum against a counter current gas flow. The counter current gas flow serves to minimize or prevent undesired neutral species (particles and molecules) from entering the vacuum, thereby minimizing or eliminating neutral species condensation with sample ions in the free jet expansion, and eliminating neutral species contamination on electrode surfaces. The electric fields and electrode geometries are optimized to maximize DSA ion source mass spectrometer sensitivity. The DSA source enclosure minimizes and/or prevents any exposure of high voltage or electric fields to the user. The mapping of sample holder types and sample positions using position sensors, to constrain sample holder and reagent ion generator translation within the ion source, minimizes and/or prevents unwanted contact with electrode surfaces by samples or moving ion source hardware during sample analysis.
The disclosure features apparatus that include a sealed enclosure which reduces and/or prevents ambient contamination from entering the ion source volume. Such ambient species can unpredictably affect ionization of sample species or contribute to unwanted interference or chemical background noise in the mass spectra. The enclosure allows tighter control of the reagent ion species generated in the ion source volume, enabling maximum and reproducible ionization efficiency and higher ionization specificity for a given sample species.
Purge gas flow is configured to sweep the ion source of gas phase sample molecules to reduce the time required between sample analysis and to minimize cross contamination between samples. Purge gas exits through a vent port where it is exhausted through a safe laboratory vent system. The sealed enclosure with safe gas purging minimizes and/or prevents exposure to the user of volatilized sample species. In some embodiments, the ion source vent, through which the reagent ion generator gas flow, the counter current gas flow and the purge gas flow exit, is positioned above the sample loading plate in the sample loading region. Gas flow into the DSA source chamber flows by the sample loading plate during sample loading, reducing and/or preventing ambient gas contamination from entering the ion source while the sample loading door is open. When the sample loading door is closed, gas flowing over and above the sample loading plate and out the vent serves to purge the sample loading volume of ambient gas prior to moving the samples into the DSA source volume. This purge process in the sample loading region can also be used to dry the newly loaded sample if this is desirable for a given sample type. A moisture or humidity sensor positioned in the vent port or line provides feedback to control systems and software regarding the degree of dryness achieved prior to moving the newly loaded samples into the DSA source volume. Measuring the degree of dryness of each sample loaded provides a way to improve consistency in the moisture remaining (or not remaining) in the sample, which can provide improved consistency in multiple sample analysis. Samples prepared on different days can be conditioned in the DSA system to improve the uniformity of analytical results for the same sample types. For example, the same type of medicinal pills prepared and run on different days can be dried consistently prior to analysis to improve the uniformity of the sample pill surface being analyzed.
The sealed enclosure is removable to facilitate ion source cleaning In some embodiments, the enclosure includes an access door that is sealed when closed. The access door and enclosure have safety sensors that turn off voltages and heaters when the DSA source enclosure seal is broken.
In some embodiments of the DSA source, sample holder translation and reagent ion generator translation can be operated in fully automated mode or with selective manual position adjustment. The position sensor inputs to the software enable the software and electronics control system to set constraints on the sample holder and reagent ion generator translation to prevent hardware collisions or electrical shorting in either automated or manual translation operation. Ion source control systems are linked to sample lists to provide correlation between generated mass spectrometer data and sample positions on multiple sample holders.
Some embodiments include the capability for software-controlled x-y-z translation of the sample and recording of the sample spot position, which enables spatial scanning during mass spectra acquisition. For example, the sample analysis spot can track sample separation lines on thin layer chromatography traces of sample mixtures.
The disclosure also encompasses DSA system control software that provides specific ionization method information per sample to the mass spectrometer data evaluation software to optimize data evaluation of acquired data and report generation. Data dependent feedback can be applied to the DSA system control software to adjust sample ionization conditions to improve performance.
The disclosure features single or multiple means of ionizing samples. Ionization means include but are not limited to reagent ion and charged droplet generation using electrospray, Atmospheric Pressure Chemical Ionization, photoionization, corona discharge and glow discharge employed singularly or in combination. Sample ionization means include but are not limited to charged droplet absorption and ion generation from evaporating charged droplets, gas phase charge exchange or energy exchange reactions, chemical ionization, photoionization and laser ionization individually or operating with combinations of ionization types.
The DSA System can be used to analyze many states of matter including but not limited to solids, liquids, gases, emulsions, powders, heterogeneous and multiphase samples and mixtures thereof.
Like reference symbols in the various drawings indicate like elements.
Open ion sources configured for direct analysis of samples are subjected to variations in the composition of background air and expose the end user to the sample being analyzed and any reagent species being deployed in the analysis. Gaseous reagent species and volatilized sample material can be inhaled by end users running the analysis. This exposure can be particularly dangerous when analyzing drugs, newly synthesized compounds, medicinal samples, diseased tissue, toxic materials or even unknown samples as in forensic samples with no available history. When operating open ion sources, changes in the background gas composition can affect ionization efficiency, contribute background contamination, add interfering component peaks to mass spectra, change reagent ion composition and temperature unpredictably, leading to unpredictable analytical results. The disclosure features apparatus and methods that allow the analysis of multiple samples directly introduced into an enclosed ion source volume with precisely monitored and controlled background gas composition, temperature and flow. Reagent ion generation in a DSA ion source system is tightly controlled and reproducible, increasing sample analysis robustness and reproducibility. Unlike open ion sources where users are potentially exposed to any voltages applied to electrodes, the DSA ion source system includes the application of electric fields formed from voltages applied to electrodes configured within the enclosed ion source volume. These applied electric fields direct ions through an orifice into vacuum, thereby increasing mass spectrometer analytical sensitivity.
Commercially available open ion sources typically use neutral gas flow to pull sample generated ions into vacuum. This same gas flow also entrains non-ionized contamination molecules and sweeps these unwanted species into vacuum where they can condense on sample ions or contaminate mass spectrometer electrodes in vacuum. The disclosure features apparatus and methods that include a counter current gas flow for sweeping away unwanted neutral contamination species from entering vacuum while directing sample ions through the orifice into vacuum using focusing electric fields. The DSA ion source system includes a dielectric capillary which allows separation of the entrance and exit ends, both electrically and spatially. This electrical electrode isolation allows different voltages to be applied to the capillary entrance and exit electrodes simultaneously, thereby providing optimal voltages both in the atmospheric pressure ion source and the in vacuum regions, as described in U.S. Pat. No. 4,542,293. Electrostatic focusing of ions at atmospheric pressure enables efficient sampling of ions into vacuum against a counter current drying gas, increasing sensitivity while decreasing unwanted neutral contamination gas or vapor molecules from entering vacuum.
Referring to
As shown in
Nebulization gas inlet 41 is connected to nebulization gas pressure regulator or flow controller 81, which controls the nebulizing gas flow rate through nebulizer 43. Nebulizing gas pressure regulator 81 is connected to and controlled through the DSA ion source system electronics and software control system 82. Nebulizing gas composition is typically but not limited to nitrogen or dry purified air. Liquid inlet 40 is connected to syringe pumps 58 and 59 loaded with syringes 60 and 61 respectively. Syringe pumps 58 and 59 can be run separately to deliver individual liquid species with controlled flow rate or can be run simultaneously to generate a mixed liquid compositions flow or form gradients of liquid compositions entering reagent ion generator 2. Alternatively, syringe pumps 58 and 59 can be replaced with any fluid delivery systems known in the art such as a liquid chromatography pump or pressurized liquid holding vials. For many sample types, a desirable positive polarity reagent ion is hydronium or protonated water (H3O)+ because hydronium has a very low proton affinity and will readily charge exchange in the gas phase with any molecule having a higher proton affinity. Protonated water clusters are less desirable because the proton affinity of water clusters grows with the number of water molecules in the cluster. Consequently, protonated water clusters can remove protons from protonated sample ions in the gas phase, reducing sample ion sensitivity. Due to the closed environment of the DSA source ionization region, the percentage of water in the background reagent gas can be tightly controlled to maximize hydronium ion production while minimizing protonated water clusters.
The percentage of water in the gas flowing through exit channel 49 is determined by the flow rate of water flowing through liquid inlet 40, which is nebulized in pneumatic nebulizer 43, and the total flow of nebulizer gas and auxiliary gas flowing through gas inlets 41 and 42, respectively. For example, with one liter per minute of nebulizer gas flowing through inlet 41, and syringe pump 58 delivering a one microliter per minute flow rate of water to nebulizer 43, after vaporization of water, which results in approximately a 1000× expansion in volume, water vapor would have a concentration of approximately 0.1% by volume flowing through exit channel 49 and corona or glow discharge 47. The percentage of water in this reagent ion gas flow can be accurately adjusted by changing the flow rate delivered by syringe 58 or the gas flow rates passing through gas inlets 41 and 42. Corona or glow discharge 47 ionizes the nitrogen gas molecules flowing through it, which in turn forms hydronium ions through a series of gas phase reactions known to those skilled in the art. The heated reagent ion gas exiting reagent ion generator exit channel 49 at exit 50 flows through grid 24, evaporating sample deposited at sample spot 27. The evaporated sample molecules charge exchange with hydronium ions and form protonated sample ions, if the sample molecules have a higher proton affinity than the passing hydronium ions. Sample ions will be formed in region 84 downstream of sample spot 27. Formed sample ions then follow the focusing electric field lines formed by voltages applied to nose piece electrode 13 and capillary entrance electrode 12 and the grounded or zero volt sample holder 22. Driven by the electric field, sample ions move against dry nitrogen counter current gas flow 60. Counter current gas flow 60 carries away any neutral water molecules or water clusters and dries protonated water clusters moving with the electric field, thereby reducing and/or preventing neutral water clusters from removing charge from the newly formed sample ions, and eliminating neutral molecules of sample or water from entering vacuum. Ions and neutral nitrogen gas enter vacuum through the rapidly cooling free jet expansion formed at exit end 85 of capillary orifice 30 in capillary 80 with little or no neutral molecule condensation occurring on sample ions. The DSA ion source system configured according to the disclosure provides accurate control of reagent ion production and delivery, enabling robust, consistent and reproducible analytical operation. As is desired, the sample itself is the one variable being analyzed, because of the reproducible controls and conditions surrounding the sample during operation.
Samples with low proton affinity in the case of positive ions may be ionized using reagent ion composition different from water. For example, a sample molecule may not accept a proton from a hydronium ion if it does not have protonation sites, but may form an attachment with a protonated ammonia ion to form a sample ion with an attached ammonia ion. Such gas phase reactions are known in the field of Atmospheric Pressure Chemical Ionization (APCI) and vacuum Chemical Ionization (CI). Ammonia can be delivered into reagent ion generator 2 in liquid form using syringe pump 58 or 59 as was described for water above, or ammonia can be drawn off as head space gas 90 or 91 in vials 87 or 88 respectively. Flow control of head space gas from vials 87 and 88 is provided by pressure regulator 92 and valve 95. Head space gas flow from either one or both vials 87 and 88 can be selected by opening or closing valves 96 and 97 respectively. Head space gas 90 or 91 flows through connection 99 and inlet 42 into heater 44. Alternatively, different auxiliary gas flow species 98 can be introduced into reagent ion generator 2 through inlet 42. Auxiliary gas flow 98, controlled through gas flow controller 93 and valve 94, may be supplied from a pressurized gas tank. For example, it may be desirable to introduce helium as a reagent gas because ionized and metastable helium formed in corona or glow discharge 47 has a high ionization potential, which improves charge transfer efficiency when these helium metastable or ion species collide with a gas phase atom or molecule. Helium is a relatively expensive gas and may not be needed to ionize many sample species. Helium can be mixed with nitrogen or other gases to form a reagent ion mixture. Valves 94, 95, 96 and 97, pressure regulators 92 and gas flow controller 93 are connected to DSA source electronics and software controller 82 to provide software and automated control of some or all gas and liquid flows into reagent ion generator 2. Alternatively, the auxiliary gas composition and flow can be controlled manually.
As shown in
Reagent ion generator 2 can alternatively be operated as an Atmospheric Pressure Chemical Ionization probe in which a sample is ionized directly. With sample holder assembly 3 moved away from the region 84 between reagent ion generator exit 50 and nose piece entrance 70, ions generated in corona discharge 47 can be delivered directly to capillary orifice 30, driven by applied electric fields as described above. Effectively, the reagent ion generator 2 can be operated as a field-free APCI inlet probe, as described in U.S. Pat. No. 7,982,185. For example, gas samples from a gas chromatograph can be delivered through inlet 40 directly into heater 44 to avoid sample component condensation. The gas chromatography carrier gas is typically helium which provides efficient ionization of the eluting gas samples as they pass through corona or glow discharge 47. Alternatively, gas samples can be introduced into reagent ion generator inlets 41 or 42 allowing the introduction of additional reagent ion species in parallel to maximize ionization efficiency. Liquid samples can also be introduced through inlet 40 from liquid chromatographs, injection valves or other fluid flow systems known to those in the art. For example, calibration solution, flow injected from syringe 58 through 40, is nebulized in pneumatic nebulizer 43, vaporized as the nebulized droplets pass through heater 44 and ionized as the calibration vapor passes through corona or glow discharge 47. The calibration ions directed into mass spectrometer 78 through capillary orifice 30 can be used to tune and calibrate mass spectrometer 78. In a similar manner, such calibration ions can also be added during sample 27, or any other sample, ionization to provide internal standard calibration ions for accurate mass measurements in higher resolving power mass spectrometers. Mass spectrometer 78 may be, but is not limited to, a quadrupole, triple quadrupole, Time-Of-Flight (TOF), Hybrid Quadrupole Time-Of-Flight, Orbitrap, Hybrid Quadrupole Orbitrap, 2D or 3D Ion Trap, Time-Of-Flight—Time-Of-Flight or Fourier Transform type mass spectrometer.
Referring to
Referring to
Sample molecules are evaporated from sample 102 due to heated reagent gas and ions 55 exiting from reagent ion generator exit 50 impinging on sample tube 101. Sample 102 is deposited on and/or loaded in glass tube 101 mounted on sample holder 110. Evaporated sample molecules may be absorbed into the electrosprayed charged liquid droplets. Sample ions are then formed as the charged liquid droplets evaporate, moving toward nose piece electrode orifice 70 against heated counter current drying gas 60, forming ions as the charged droplet evaporation proceeds, as is known in the art. Alternatively, reagent ions possibly with multiple charges formed from evaporating electrospray droplets can charge exchange with gas phase sample molecules to form sample ions that are then directed into capillary orifice 30 and on to mass spectrometer 78 for mass to charge analysis as described above. Gas phase sample molecules from sample 102 can be exposed to reagent ions 55 exiting reagent ion generator 2 or electrospray generated reagent ions or charged droplets individually or simultaneously. Selection of reagent ion or charged droplet sources is achieved by controlling voltages applied to corona or glow discharge needle 48 and electrospray needle 103 and by controlling fluid flow or nebulization and reagent gas sources 111, 58, 59, 87, 88 and 98.
Sample gas may be introduced directly into ionization region 84 where ionization occurs through charge exchange with reagent ions or metastable species formed from corona or glow discharge 47 or electrospray 103 sources. Resulting sample ions are then directed into mass spectrometer 78 for mass to charge analysis as described above. Referring to
Sample heating is an important variable to control to achieve reproducible, consistent and reliable sample ionization efficiencies. Different samples have different heat capacities and may require different temperatures to effect sample molecule evaporation. In some embodiments, the enthalpy required to heat a sample surface can be controllably delivered from multiple sources. One source of heat applied to a sample surface is delivered as heated reagent ion gas from reagent ion generator 2 as described above. The amount of enthalpy delivered to a sample surface from reagent ion and gas flow 55 exiting exit 50 of reagent ion generator 2 is a function of exiting gas and ion mixture 55 temperature and flow rate. Gas and reagent ion temperature is controlled by setting the temperature of heater 44 with some addition of heat from corona or glow discharge 47. Total gas flow rate passing through reagent ion generator 2 exit 50 is described above. Alternatively, or in addition, heat can also be delivered to a sample surface using a light source.
Referring to
Heating light source 7 can be configured with an exit lens which focuses the emitting light to a smaller spot on a sample surface than can be achieved using heated gas flow. This focused source of heat allows improved spatial resolution on surfaces when analyzing solid phase samples or other sample types. Referring to
The intensity of heating light or laser 8 can be rapidly adjusted because it is not subject to the heat capacity of a heater element as is the case with reagent ion generator heater 44. Adjustment of the gas temperature of reagent gas 55 exiting exit channel 49 takes a longer time due to the heat capacity of the total gas flow path in reagent ion generator 2 and to the heat generated by corona or glow discharge 47.
DSA ion source system 1 can be configured with video camera 10 with or without fiber optic probe 11. Video camera 10 with correct positioning can be used to view the sample surface location being analyzed and feed back to software or the user the visual status of the surface at any time during the analysis. The four axis sample holder assembly 3 translator control determines the precise location of a given sample surface relative to mass spectrometer 78 capillary sampling orifice 30. The known sample position is correlated to acquired mass spectral data and can also be correlated to video images during sample analysis. Video camera 10 includes appropriate light optics lenses to provide magnification of sample surfaces. With the appropriate optics, video camera 10 can be configured outside enclosure 14 to minimize exposure of video camera 10 to the sample environment and to reduce and/or eliminate any degassing of the camera enclosure or electronics. Such degassing would add undesirable background chemical species inside enclosure 14 of the DSA ion source system 1.
Angled reagent ion generator 2 shown in
A smaller DSA ion source 1 and enclosure 14 volume includes less volume to purge of gas phase contaminants between each sample analysis and when loading and unloading of sample holder assemblies 3110, 132 and 162. Less gas usage is required to effectively purge a smaller source volume and less time is required to remove contamination gas species prior to starting a new sample analysis set or between each sample analyzed. Faster purging of contaminant species allows faster analysis times for multiple sample sets improving overall ion source analytical efficiency.
Referring to
The position of reagent ion generator exit 50 can be adjusted manually or automatically during acquisition to maximize ion signal using data feedback. Four axis translator 150 can be adjusted by software based on acquired mass spectrum data and position sensor feedback. Such data dependent mechanical tuning of the sample and reagent ion generator positions can be automated using the appropriate algorithms. With such automated tuning algorithms available, different sample types, shapes and sizes can be loaded and sample and reagent ion generator positions can be adjusted automatically for optimal performance with little or no user intervention.
Reagent ion generator rotatable angle end assembly 134 includes removable end piece 140 shown in
One or more heating light sources 7 can be mounted to rotatable angled end assembly 134 that includes rotating ring 141 so that heating light 125 automatically remains oriented in the direction of heated reagent gas and reagent ion flow 55 when end assembly 134 is rotated. Similarly, pyrometer 8 can be mounted to rotatable angled end assembly 134 positioned to point at the sample location impinged by heating light source 7 and heated gas and reagent ions 55. Alternatively, one or more heating light sources 7 and one or more pyrometers 8 can be positioned independently of reagent ion generator 2 position and translationally referenced instead to the sample position and fixed position nose piece 13 with appropriate translationally adjustable mounting bracket assemblies.
In some embodiments, sample holder assemblies 3, 100, 132 and 162 shown in
In the embodiments shown in
Four axis sample holder translator assembly 180 includes two rotation seals and one slider rotation seal that provide tight gas sealing through envelope 187 base 189 during all four axis motion while creating no detectable chemical contamination inside enclosure 187. Circular shaft seal 340 provides a rotating and sliding seal to outer shaft 302. Shaft seal 341 provides a rotating seal against middle shaft 301 and shaft seal 342 provides a rotating seal against inner shaft 300. Seal material includes teflon or other material that provides an effective gas tight seal while having no contribution to background gas phase contamination inside envelope 187. Four axis translation assembly 188 provides a wide range of rotational and linear motion that includes only rotating and circular sliding gas tight seals. No leaky or potentially sticky linear seals are used. Evaporated sample molecules are effectively trapped in sealed envelope 187 and swept out vent port 344 into a safe laboratory vent system, preventing any exposure to the user. Conversely, ambient contamination is prevented from entering enclosure 187 during analysis, thereby providing operating and analytical benefits as described above.
Four axis translator assembly 180 provides the complete range of motion required for sample shape and surface profiling, sample position checking, optimized analysis, loading and unloading of sample holder assemblies, and for effecting full sample holder plate profiling to determine sample holder type, sample type, numbers, positions and heights prior to analysis.
Referring to
In conjunction with continuously flowing purge gas 352, minimizing contamination cross talk between samples can be achieved by moving sample holder 3, 110, 132, 162, 190 or 371 to a position where the regent ion generator exiting gas flow 55 or any light heat sources do not impinge on a sample position or sample holder surface. For example, lowering the position of sample holder assembly 190 in
When some or all pills 360 mounted on sample holder assembly 190 have been analyzed, sample holder assembly 190 is moved to the unload position in opening 364 of sample loading and unloading region 363. Purge gas flow 365 continues to sweep by sample holder assembly 190 through gap 391 between sample holder 192 and opening 364 and out vent port 344. When moving sample holder assembly 190 to its load and unload position, four axis translator assembly 180 passes through or by position sensors 367, 350 and 368 to reset the reference location of horizontal linear axis translator assembly 312 and sample holder assembly 190 rotation axis 182 respectively. Four axis translator vertical linear axis 185 and rotation axis 184 zero positions are also revalidated by position sensors located below base plate 185 outside envelope 187. Referencing
Referring to
Referring to
During this purging of region 363 after sample loading region, reagent ion generator 2 remains turned on with mass spectra being acquired to check the level of background chemical contamination in DSA source volume 354. The sample loading purge cycle as described above can continue until the ambient background signal is sufficiently reduced as determined by data dependent feedback through evaluation of mass spectra acquired during the post sample loading purge cycle. Calibration solution can be introduced into reagent ion generator 2 as described above to tune and calibrate mass analyzer 78 before samples 383 are run. With continued purging, when the background chemical noise level observed in acquired mass spectra has reduced to an acceptable level and/or, if desired, the moisture level in venting purge gas 365 is sufficiently low, sample holder assembly 371 with samples 383 loaded is lowered into DSA ion source region 387.
Referring to
Using distance sensor 150 and sample holder translator 180 the number, location and height of each sample tube 382 are mapped and matched to the sample list loaded into software. Using the sample holder plate identification and sample position mapping information generated by distance measuring sensor 350 and bar code reader 392, sent to software and electronics controller 82, software adjusts the position of reagent ion generator 2 and rotatable angle exit assembly 134. Motorized angled linear axis translator 153 position is moved to its extended position in reagent ion generator four axis translator assembly as described for
Distance sensor 150 can be used to map the contour of sample surfaces enabling software algorithms to set the optimal position of the sample for analysis. Four axis translator 180 moves a sample under the laser beam of distance sensor 150 to produce a map of the surface elevations and the edges of the sample. For example, if an orange peel is loaded into DSA ion source system 1, as shown in
Referring to
DSA ion source system 1 can be configured with means to generate sample ions without the need for reagent ion generator 2. Referring to
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
This application claims benefit of Provisional Application No. 61/493,255, filed on Jun. 3, 2011, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61493255 | Jun 2011 | US |
