The present disclosure relates to a mass spectrometer system, and more particularly, to a mass spectrometer system having an external detector.
Chemical analysis tools such as gas chromatographs (“GC”), mass spectrometers (“MS”), ion mobility spectrometers (“IMS”), and various others, are commonly used to identify trace amounts of chemicals, including, for example, chemical warfare agents, explosives, narcotics, toxic industrial chemicals, volatile organic compounds, semi-volatile organic compounds, hydrocarbons, airborne contaminants, herbicides, pesticides, and various other hazardous contaminant emissions. Mass spectrometers measure the atomic mass of a material's constituent molecules and report the masses of these molecules and their relative abundance. This information is used to identify the material. Mass spectrometers may be considered the gold standard for chemical analysis.
As chemical analysis has become a more routine part of many industries, a need has developed for smaller, lighter mass spectrometers that can be incorporated more easily into laboratory and industrial settings and that have lower initial instrument costs and continued operating costs. Additionally, there is a need for portable mass spectrometers that may be used to detect analytes in the field, that have low power requirements and a small size. There are, however, physical limits to the miniaturization of mass spectrometers.
Conventional mass spectrometers may include an ion source, an ion trap, and an ion detector. In smaller devices, these components may be encased within a chamber having an interior volume of approximately 30 cm3. In some instances, the ion detector can occupy more chamber space than the ion source and the ion trap combined.
The location of the ion detector within the chamber can be problematic. For example, the output signal of the detector may be subject to the high voltage RF signal applied to the ion trap. This may result in noise or corruption of the detector signal. Further, the electrical connections required to output the detector signal to processing equipment can add to the size, complexity, and cost of mass spectrometers.
The ion detector typically operates under a vacuum environment, requiring pressures in the range of 10−3 to 10−8 Torr for proper operation. Mass spectrometers thus employ pumps, often a system of vacuum pumps, to achieve these pressures, which account for the size and cost of mass spectrometers. The size of the chamber and the corresponding pump system are often limiting factor on the ability to further reduce the size of conventional mass spectrometers.
The size of the chamber has other drawbacks. Because of the relatively large interior volume of the chamber, low volatility compounds such as, for example, explosives and narcotics, may stick to surfaces of the chamber and remain in the chamber after use. These chemicals may outgas slowly and create false leaks or detections, which can be problematic.
Additionally, the large volume of the chamber, as compared to the small volume of the ion trap, means that only a small fraction of the analyte introduced to the system is trapped and analyzed. As a result, the overall sensitivity of the system is reduced. This is an issue where, for example, the mass of an analyte (not concentration) is to be detected.
The present disclosure is directed to a mass spectrometer that addresses one or more of these concerns.
The present disclosure relates to a mass spectrometer system, and more particularly, to a mass spectrometer ion trap having an external detector reduce the volume within the vacuum chamber.
One embodiment of the disclosure is directed to a mass spectrometer system. The mass spectrometer may include a vacuum chamber defining an enclosed evacuated space and an ion trap disposed in the enclosed space. The ion trap may be configured to trap an ionized sample. The mass spectrometer may further include an ion detector coupled to the chamber at a location external to the chamber, such that sample ions may exit the evacuated space and into the externally-coupled detector without loss of vacuum pressure.
In various embodiments, the mass spectrometer may include one or more of the following features: wherein the chamber includes an aperture configured to direct ions ejected from the ion trap to the detector; further including a pump to maintain the chamber under vacuum, wherein the externally-coupled detector is housed in a portion of the mass spectrometer that is not under vacuum; wherein the ion detector includes an internal detector tube under vacuum; wherein the tube includes an input end and an output end, wherein the input end is configured to engage a wall of the chamber to provide a pressure barrier so as to maintain the chamber and an interior of the tube under vacuum; wherein the output end is sealed from the ambient air; and wherein the chamber has a volume to accommodate only an electron source and the ion trap.
Another embodiment of the disclosure is directed to a mass spectrometer system. The mass spectrometer system may include a chamber configured to be maintained under vacuum. The chamber may include an ion trap being configured to capture ions generated when a sample is ionized by the electrons emitted from an electron source; and an ion detector configured to detect ions ejected from the ion trap. The ion detector may include a tube configured to be maintained under vacuum. The tube may be coupled to a wall of the chamber at a location external to the chamber.
In various embodiments, the mass spectrometer may include one or more of the following features: wherein the wall of the chamber defines a recess; wherein the tube includes an input end, and wherein the input end is configured to be received in the recess to couple the ion detector to the chamber; further including an o-ring disposed between the input end and the wall in the recess, wherein the o-ring is configured to provide a sealing interface between the input end and the recess; wherein the recess includes a groove to receive the o-ring; further including a fastener to exert pressure onto the tube to press the first end into the recess; wherein the input end is sized to be press-fit into the recess; and wherein the tube includes a fastening assembly configured to position the detector relative to the wall so that an input end of the tube is flush against an outer surface of the wall.
Another embodiment of the disclosure is directed to a mass spectrometer system. The system may include a chamber defining an enclosed space configured to be maintained under vacuum. The chamber may include an ion source configured to emit electrons and an ion trap. The ion trap may include a ring electrode; and first and second end cap electrodes which are arranged on opposite sides of the ring electrode. The first end cap electrode includes a first aperture through which the electrons emitted by the electron source enter the ion trap, and the second end cap electrode includes a second aperture through which ions are discharged from the ion trap. The system may further include an ion detector configured to detect an amount of ions ejected from the ion trap, the ion detector being coupled to the chamber at a location external to the chamber.
In various embodiments, the mass spectrometer may include one or more of the following features: further including an amplifier coupled to the ion detector at a location external to the chamber; wherein the ion detector is a discrete dynode electron multiplier; wherein the ion detector is a channel electron multiplier; and wherein the ion detector includes a vacuum tube having an input end and an output end, wherein the input end sealingly engages a wall of the chamber.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings illustrate certain embodiments of the present disclosure, and together with the description, serve to explain principles of the present disclosure.
Reference will now be made in detail to an exemplary embodiment of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
The disclosure relates generally to instruments for chemical analysis such as, for example, mass spectrometers. The term “mass spectrometer” is used broadly to refer to any components and systems that may be used to detect or identify analytes using mass-to-charge ratios. The terms “analyte,” “sample,” “material,” “chemical,” and “ions” may all be used herein to refer to a substance to be analyzed and identified. Such substances include, but are not limited to, gases, proteins, residues and vapors from explosives, chemical warfare agents, toxic chemicals, food and beverage contaminants, and pollution products.
As shown in
Chamber 110 may be coupled to a vacuum path via one or more ports (not shown) so as to create a low pressure (e.g., vacuum) environment within space 110c of chamber 110 for chemical analysis. In some embodiments, the pressure in enclosed space 110c is in the range of 10−3 to 10−8 Torr. It is contemplated that a series of pumps (not shown) may be employed to achieve the desired operating pressure.
In operation, chamber 110 may be configured to receive a sample and convey the sample to ion trap 119 through one or more inlets (not shown). Electron source 111 may be configured to emit electrons to ionize the sample, and ion trap 119 may be configured to capture the ions and separate one or more of the ions for detection by a detector 117. Detector 117 may be positioned outside chamber 110, to reduce the volume within space 110c of chamber 110, and provide a miniaturized mass spectrometer system 100.
As shown in
In the exemplary embodiment, electron source 111 is a filament. Filament 111 may be connected to a power source (not shown). The power source may be removably coupled at an exterior location relative to chamber 110 or, alternatively, the power source may be permanently or removably coupled to chamber 110. The power source may be any suitable source of power configured to, for example, heat filament 111. As noted above, heated filament 111 may be configured to emit electrons.
A first lens 112 is disposed between electron source 111 and ion trap 119. First lens 112 may be any suitable optical component known to one of ordinary skill in the art configured to focus the electrons emitted from electron source 111 into, for example, an electron beam. In this manner, first lens 112 may be configured to adjust a percentage of electrons that enter ion trap 119, and thus control the rate of ionization within the trap. In some embodiments, first lens 112 may be coupled to a controller (not shown). The controller may be configured to modulate the potential and polarity of lens 112 to change the shape of the electron beam directed at ion trap 119 and to gate the electron beam so that no new ions are generated during the ejection phase of the mass scan.
Ion trap 119 is configured to capture ions introduced or created within chamber 110 or within ion trap 119, and eject one or more ions for detection by detector 117. Ion trap 119 may be any suitable type of trap including, for example, a quadrupole ion trap or a linear ion trap employing electric fields for operation. In the exemplary embodiment, ion trap 119 is a cylindrical ion trap.
As shown in
First and second end cap electrodes 113, 115 may include any suitable shape and/or orientation in ion trap 119. First and second electrodes 113, 115 may also include any suitable conductive material (e.g., copper, silver, gold, platinum, iridium, platinum-iridium, platinum-gold, conductive polymers, stainless steel, etc.) or combinations of conductive (and/or noble metals) materials. In the exemplary embodiment, first and second end cap electrodes 113, 115 may be flat electrodes.
First end cap electrode 113 defines a first aperture 120 through which the electrons emitted by the electron source enter ion trap 119. Second end cap electrode 115 defines a second aperture 124 through which ions are discharged from ion trap 119. First aperture 120 and second aperture 124 may have any length, size, shape and/or configuration. It is contemplated that first aperture and second aperture may have the same or different sizes and/or shapes. It is further contemplated that the geometric parameters of first aperture 120 and second aperture 124 may be selected to provide increased or optimum performance with respect to mass spectrometer system 100.
Ring electrode 114 may be disposed between first end cap electrode 113 and second end cap electrode 115. For example, ring electrode 114 may be disposed half-way or centered between the first end cap electrode 113 and second end cap electrode 115. In some embodiments, the distance between the first and second end cap electrodes 113, 115 and/or the distance between each of first and second end cap electrodes 113,115 and ring electrode 114 may be arranged so as to optimize the electric field generated within ion trap 119.
Ring electrode 114 may have any suitable shape, size and/or configuration in ion trap 119. Ring electrode 114 may also include any suitable conductive material (e.g., copper, silver, gold, platinum, iridium, platinum-iridium, platinum-gold, conductive polymers, stainless steel, etc.) or combinations of conductive (and/or noble metals) materials. In the exemplary embodiment, ring electrode 114 may be cylindrically shaped defining an opening therein. The opening may be aligned with first aperture 120 and second aperture 124. Although the depicted embodiment includes a single opening 128, it is contemplated that a greater or lesser number of openings may be provided in ring electrode 128.
Ion trap 119 may be configured to dynamically trap the ions in a quadrupole field within the spaced defined by first end cap electrode 113, second end cap electrode 115, and ring electrode 114. This field may be created through application of radio-frequency (RF) and direct current (DC) voltages to ring electrode 114 relative to first and second end cap electrodes 113, 115. The voltages applied to ring electrode 114 may be altered in order to selectively destabilize different masses of ions held within ion trap 119. The destabilized ions may be ejected from the ion trap 119 via second aperture 124.
As shown in
Detector 117 is configured to detect the number of ions emitted from ion trap 119 at different time intervals that correspond to particular ion masses. Detector 117 may be of a type and kind well known in the art. Exemplary detectors include electron multipliers, photographic detectors, and stimulation-type detectors. In the exemplary embodiment, detector 117 may be a single-particle detector such as, for example, a discrete dynode electron multiplier or a channel electron multiplier.
In the exemplary embodiment shown in
Tube 150 may have any size, shape, and/or configuration, and may be any desired dimension for use in the miniaturized mass spectrometer system 100. In some embodiments, a portion of tube 150 adjacent input end 152 may be shaped to facilitate detection of one or more ions. In the exemplary embodiment, tube 150 includes a horn 150a having a conical shape that tapers from input end 152 towards output end 153. It is contemplated that, in some embodiments, tube 150 may include a cylindrical input end 152 having, for example, an enlarged diameter. The remainder of elongate member 120 may, for example, define a cylindrical shape having a substantially circular cross section. It is contemplated that, in some embodiments, the remainder of tube 150 may be curved.
In an exemplary embodiment shown in
The ejected ions may be received in channel 154 via input end 152. In channel 154, ions may contact the coating and, upon contact, may induce the emission of multiple electrons. In this manner, the ejected ions may produce, in a cascade multiplication process, current. The electrons may be configured to contact a plate or target at output end 153, which may then generate a signal.
Referring back to
As alluded to above, detector 117 is positioned at an external location relative to chamber 110 so as to reduce the volume of chamber 110. In this way, by allowing the volume of the vacuum chamber to be smaller, mass spectrometers 100 consistent with the disclosed embodiments may use smaller and less expensive vacuum pumps (not shown in
An o-ring 160 may be positioned between input end 152 of detector 117 and second wall 110b of chamber 110. O-ring 160 may be configured to facilitate sealing engagement between input end 152 and recess 129. O-ring 160 may be fabricated from an elastomeric, low friction material, and may be configured to provide a sealing interface between detector 117 and second wall 110b. O-ring 160 may have any size, shape, thickness, or cross-section. In alternative embodiments, a copper seal may be used in place of o-ring 160. In the exemplary embodiment of
A fastener 170 may be provided to press input end 152 against o-ring 160. Fastener 170 may be any type or kind known to one of ordinary skill in the art including, bolts, screws, etc. As shown in
O-ring 160 may be configured to allow detector 117 to be externally mounted to vacuum chamber 110 without any loss of vacuum pressure in chamber 110. The sealing engagement of input end 152, o-ring 160, and second wall 110b in recess 129a may provide a pressure barrier so that enclosed space 110c of vacuum chamber 110 and channel 154 may be maintained at low pressures. It is contemplated that, in some alternative embodiments, o-ring 160 may be placed about horn 150a. In those embodiments, groove 129a is not provided. O-ring 160 may sealingly engage bolt 170, horn 150a, and recess 129 to maintain the low pressure in enclosed space 110c and channel 154.
As in the embodiment described above, input end 252 may be coupled to second wall 110b of chamber 110 so as to maintain a vacuum environment in enclosed space 110c and space 254 of housing 250. More particularly, input end 252 of detector 117 may be configured to engage recess 129, so as to couple detector 117 to chamber 110. In some embodiments, input end 252 may be sized to securely fit in recess 129 by, for example, being press-fit into recess 129. In other embodiments, input end 252 may be threadably coupled to recess 129. When input end 252 is received in recess 129, aperture 251 on input end 252 may be aligned with aperture 128 of second wall 110b to receive emitted ions from ion trap 119.
As in the embodiment described above, an o-ring 160 may be positioned between input end 252 of detector 117 and second wall 110b of chamber 110. As in the embodiment described above, o-ring 160 is disposed between input end 152 and second wall 110b in recess 129 in an annular groove 129a in recess 129. Annular groove may include one or more protrusions 129b to retain o-ring 160 in groove 129a.
O-ring 160 may be configured to allow detector 117 to be externally mounted to vacuum chamber 110 without any loss of vacuum pressure in chamber 110. It is contemplated that, in some additional embodiments, a fastener may be positioned about housing 250 to fasten housing 250 to second wall 110b of chamber 110. In those embodiments, the fastener may be configured to exert pressure on tube 250 so as to press input end 252 into recess 129 and onto o-ring 160. This, in turn, may provide a pressure barrier so that enclosed space 110c of vacuum chamber 110 and the interior of housing 250 may be maintained at low pressures.
Fastening assembly 380 may include a bolt having one or more apertures to receive one or more screws. In the exemplary embodiment, bolt 382 includes two apertures to receive two screws 381a and 381b. Each screw 381a, 381b may include threads that may be designed to mate with a complementary thread. In the exemplary embodiment, screws 381a and 381b may engage second wall 110b to couple detector 117 to an outer surface of second wall 110b. More particularly, during assembly, input end 352 may be positioned adjacent to, or flush with, an outer surface of second wall 110b so that a channel (not shown) may be in communication with aperture 128 of second wall 110b. Screws 381a and 381b may then be configured to engage second wall 110b to provide a sealing interface so as to maintain the low pressure in enclosed space 110c and housing 350.
Embodiments described herein may have several benefits. By mounting detector 117 externally, chamber 110 may no longer need one or more electrical connectors or ports, which are typically used to provide power to detector 117. This may reduce the cost and complexity of mass spectrometer system 100. Additionally, the disclosed configuration may protect the detector output signal from interference caused by the RF signal applied to ion trap 119. The disclosed configuration also minimizes the surface area inside chamber 110, by allowing only the interior surface of detector 117 to be exposed to the chamber interior 110c.
Additionally the disclosed embodiments may operate to reduce the size of chamber 110 so that mass spectrometer system 100 may be used in places where conventional units could not be used because of cost and the size of the conventional units. For example, mass spectrometer 100 may be placed in a hazard site to analyze gases and remotely send back a report of conditions presenting danger to personnel. Mass spectrometer 100 using embodiments herein may be placed at strategic positions on air transport to test the environment for hazardous gases that may be an indication of malfunction or even a terrorist threat. The present disclosure has anticipated the value in reducing the size required to make a functioning mass spectrometer so that its operation may be used in places and in applications not normally considered for such a device.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
The application claims priority to Provisional Application No. 61/800,732, filed Mar. 15, 2013, and titled “A MASS SPECTROMETER HAVING AN EXTERNAL DETECTOR,” all of which is incorporated herein by reference.
Number | Date | Country | |
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61800732 | Mar 2013 | US |