Method and apparatus for chromatography-high field asymmetric waveform ion mobility spectrometry Number:6,815,668 from the United States Patent and Trademark Office (PTO) owispatent Method and apparatus for chromatographic high field asymmetric waveform ion mobility spectrometry, including a gas chromatographic analyzer section intimately coupled with an ionization section, an ion filter section, and an ion detection section, in which the sample compounds are at least somewhat separated prior to ionization, and ion filtering proceeds in a planar chamber under influence of high field asymmetric periodic signals, with detection integrated into the flow path, for producing accurate, real-time, orthogonal data for identification of a broad range of chemical compounds.<H chromatography, spectrometry, Method, and, appa, 6815668.html, Patent, pto, 6815668

Title: Method and apparatus for chromatography-high field asymmetric waveform ion mobility spectrometry

Abstract: Method and apparatus for chromatographic high field asymmetric waveform ion mobility spectrometry, including a gas chromatographic analyzer section intimately coupled with an ionization section, an ion filter section, and an ion detection section, in which the sample compounds are at least somewhat separated prior to ionization, and ion filtering proceeds in a planar chamber under influence of high field asymmetric periodic signals, with detection integrated into the flow path, for producing accurate, real-time, orthogonal data for identification of a broad range of chemical compounds.

Patent Number: 6,815,668 Issued on 11/09/2004 to Miller, et al.

Inventors: Miller; Raanan A. (Cambridge, MA); Nazarov; Erkinjon G. (Las Cruces, NM); Eiceman; Gary A. (Las Cruces, NM); Krylov; Evgeny (Las Cruces, NM); Tadjikov; Boris (Las Cruces, NM)
Assignee: The Charles Stark Draper Laboratory, Inc. (Cambridge, MA)

Appl. No.: 799223

Filed: March 5, 2001

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
358312	Jul., 1999	6495823

Current U.S. Class: 250/286 ; 250/281; 250/282; 250/287; 250/288

Field of Search: 250/281,282,286,287,288

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Primary Examiner: Lee; John R.
Assistant Examiner: Gurzo; Paul M.
Attorney, Agent or Firm: Ropes & Gray LLP

Parent Case Text

This application is a continuation-in-part of Application Ser. No. 09/358,312 filed Jul. 21, 1999 now U.S. Pat. No. 6,495,823.

Claims

What is claimed is:

1. Apparatus for characterization of a chromatographic eluent, comprising: an input part, an ion filter part for filtering ions, an output part, and a flow path connecting said parts, said parts being supported by a support structure, said ion filter part including at least a pair of filter electrodes on said support structure, said flow path axis extending between said input part and said output part through said ion filter part, said input part for receiving a chromatographic eluent, said eluent including at least one analyte, said analyte being represented by a chromatographic peak that is associated with a chromatographic residence time, said peak having a peak duration in said ion filter part, said input part for delivering a flow of ions to said flow path, said flow of ions including at least one ion species associated with said analyte, said flow of ions flowing along said flow path to said ion filter part, said ion filter part filtering said flow of ions, said support structure including an electrode support in said ion filter part adjacent to said filter electrodes for support of said filter electrodes in said ion filter part, said filter electrodes being separated and forming an analytical gap in said ion filter part, said filter electrodes providing a compensated asymmetric filter field within said analytical gap, said flow path extending through said analytical gap, wherein surfaces of said flow path in said ion filter part are cooperatively defined by said electrodes and said support structure, said ion filter part for providing said compensated asymmetric field across said flow path transverse to said flow path for selection of said at least one ion species out of said flow of ions, said selection being at least in part based on mobility characteristics of said selected at least one ion species in said compensated asymmetric field, and said ion filter part passing said selected at least one ion species to said output part within said peak duration for characterizing said at least one ion species within said peak duration, said characterizing being based on said passing of said selected at least one ion species.

2. Apparatus of claim 1 further comprising a chromatograph for supply of said eluent and wherein said characterization includes identification of said analyte based on said retention time associated with said peak in said chromatograph.

3. Apparatus of claim 2 wherein said output part includes a detector for detection and identification of said at least one ion species, wherein said detection data includes (a) intensity of said at least one ion species detection, (b) said retention time, and (c) conditions of said compensated high asymmetric field.

4. Apparatus of claim 3 wherein said flow of ions includes reactant ions, wherein said detection data is compared to known data to make said identification of said at least one ion species.

5. Apparatus of claim 3 further comprising a display coupled to said output part for display of at least two dimensional data representative of said detected species.

6. Apparatus of claim 1 wherein said input part is disposed to present said chromatographic eluent in gas phase to said flow path.

7. Apparatus of claim 1 wherein said input part includes an ionization section for ionization of said analyte and said output part includes a detector for generation of detection data associated with said analyte, further comprising a control part coupled to said filter part for scanning of said field compensation, wherein said analyte is ionized in said ionization section and generates a representative flow of ions that is delivered in said flow path to said filter part, wherein said field compensation is scanned a plurality of times by said control part and wherein a plurality of mobility spectra are generated for said flow of ions, and wherein said plurality of scans has a total duration less than said peak duration, for characterizing chemical species in said eluent.

8. Apparatus of claim 7 further comprising a device housing, said control part having contacts associated with said housing for application to said ion filter part of an asymmetric field drive signal.

9. Apparatus of claim 1 wherein said input part includes a gas chromatograph and an ionization section associated with said flow path, said chromatograph delivering said eluent into said ionization section, said ionization section generating said at least one ion species.

10. Apparatus of claim 1 wherein said peak includes multiple peak aspects and wherein scanning of said compensated field is performed in said filter part for generating differential mobility spectra for said multiple peak aspects, said scanning being performed within a period of less than said peak duration, for characterizing chemical species in said eluent.

11. Apparatus of claim 10 further comprising a control part for control of said compensated asymmetric field, said control part scanning said field compensation by scanning a DC bias applied to said field.

12. Apparatus of claim 10 further comprising a control part coupled to said filter part for applying an asymmetric RF signal to said filter part to generate said compensated asymmetric field, said control part scanning said compensation by scanning an aspect of the RE signal.

13. Apparatus of claim 12 wherein said aspect is the duty cycle of the RE signal.

14. Apparatus of claim 12 further comprising a drift gas tube, wherein said capillary column is housed within said drift gas tube, said capillary column having a column outlet delivering said carrier gas and said drift gas flow surrounding said carrier gas flow at said column outlet.

15. Apparatus of claim 1, wherein said input section further includes an inlet in said flow path and a gas chromatograph having a capillary column for delivering a gas sample into said inlet, said gas sample including a compound-containing carrier gas, further including a drift gas source, said drift gas source supplying said drift gas into said inlet to carry said compound-containing carrier gas along said flow path to said output section.

16. Apparatus of claim 1 wherein said ion filter part defines a pair of electrode plates across said flow path, said compensated asymmetric field being developed between said electrode places.

17. Apparatus of claim 16 wherein said ion filter part is non-cylindrical and said filter electrodes are non-cylindrical.

18. Apparatus of claim 17 further comprising insulated substrates, said electrode plates located on said substrates in said ion filter part for formation of said filter electrodes.

19. Apparatus of claim 18 further comprising a housing, wherein said substrates are incorporated into said housing, wherein said ion filter part comprises a pair of spaced-apart electrodes facing each other over said flow path and supported by said substrates.

20. Apparatus of claim 19 wherein said filter electrodes having inner faces facing each other across said flow path for forming said filter field, said facing electrodes having outer faces positioned on said substrates.

21. Apparatus of claim 1 further comprising a pair of substrates, wherein said flow path is formed incorporating said substrates, wherein said ion filter part comprises a pair of spaced-apart electrodes facing each other over said flow path and associated with said substrates.

22. Apparatus of claim 21 wherein said field is formed between said electrodes, wherein said field is non-focusing.

23. Apparatus of claim 22 wherein said electrodes are planar.

24. Apparatus of claim 22 wherein said electrodes are parallel.

25. Apparatus of claim 22 wherein said substrates form a device housing, said device housing supporting said input part, said flow path, and said output part.

26. Apparatus of claim 1 further comprising a detector in said output part for said ion detection, said filter part passing positive and negative ions to said detector, wherein said detector includes a pair of electrodes, said electrodes biased and cooperatively enabled for simultaneous detection of said positive and negative ions passed by said filter part.

27. Apparatus of claim 1 further comprising a control part for control of said compensated asymmetric field, wherein the trajectory of said ion species passing through said field is regulated by said control part, wherein the output section further includes a detector, said detector including a plurality of electrodes in sequence to form a segmented detector, said segments separated along said flow path to detect said passed ions spatially according to their trajectories, and said control part controlling said detection.

28. Apparatus of claim 1 wherein said flow path is operable at or around atmospheric pressure in air.

29. Apparatus of claim 1 wherein said ion filter part includes an array of filters, each filter including a pair of electrodes in said flow path.

30. Apparatus of claim 1 further including a heater in said flow path.

31. Apparatus of claim 1 wherein said chromatograph is a gas chromatograph and said drift gas is air.

32. Apparatus of claim 1 further comprising an isolation part joining said ion filter part and said output part, said isolation part facilitating non-conductive connection of said ion filter part and said output part.

33. Apparatus of claim 1 further comprising a plurality of electrodes which comprises array of electrodes formed in said flow path.

34. Apparatus of claim 33 further comprising a plurality of dedicated flow paths communicating with said output section, wherein said plurality of electrodes comprises an array of filter electrode pairs associated with said dedicated flow paths.

35. Apparatus of claim 1 further comprising a pair of substrates, wherein said flow path is formed incorporating said substrates, wherein said filter electrodes face each other over said flow path and are associated with said substrates, further comprising at least one pair of detector electrodes, one said detector electrode associated with each said substrate.

36. Apparatus of claim 1 further comprising a plurality of electrodes forming a segmented detector with several segments, said segments being formed in a longitudinal sequence along said flow path in said output part.

37. Apparatus of claim 1 further comprising a flow pump for drawing a fluid gas sample through said flow path from said input part to said output part.

38. Apparatus of claim 37 further comprising a plurality of dedicated flow paths, wherein said input part includes an ionization source for said ionization of gas samples drawn by said flow pump, further comprising a second pump for recirculation of air in at least one of said flow paths.

39. Apparatus of claim 1 wherein said compensated asymmetric field is developed between said electrode plates, further comprising a pair of insulated substrates forming surfaces of said flow path, said electrode plates formed on said substrates in said ion filter part.

40. Apparatus of claim 39 further comprising a third substrate, wherein said substrates define at least two adjacent flow paths.

41. Apparatus of claim 39 further comprising a spacer extending along said flow axis between said input part and said output part and said filter electrodes cooperating with said spacer to define said gap.

42. Apparatus of claim 41 wherein said spacer cooperates with said substrates and said electrodes to form a device housing enclosing said flow path.

43. Apparatus of claim 42 wherein said spacer is silicon and defines confining electrodes in said flow path, further including a detector downstream from said ion filter part for detecting ions traveling from said filter part under control of said confining electrodes.

44. Apparatus of claim 1 further comprising a heater in said flow path for heating and purging said flow path.

45. Apparatus of claim 44 further comprising insulated substrates, said ion filter part including filter electrodes formed on said substrates, wherein filter electrodes can be used as heater electrodes.

46. Apparatus of claim 1 further comprising a control part coupled to said filter part for scanning of said field compensation in said filter part for generating differential mobility spectra for representing analytes in said eluent said scanning being performed within a period as long as or less than said peak duration and generating multiple detection data for characterizing said analytes.

47. A method for analysis of compounds in a chromatographic eluent, including the steps of: providing a high field asymmetric ion mobility filter system with an internal flow path, enabling attachment of the output of a chromatograph system to said flow path, said flow path opening into the input part of a said high field asymmetric ion mobility filter system, said system further including, an ion filter part for filtering ions, and an output part, said flow path connecting said parts, supporting said parts with a support structure, said ion filter part including at least a pair of filter electrodes, said filter electrodes being on said support structure, providing said support structure with an electrode support in said ion filter part adjacent to said filter electrodes for support of said filter electrodes in said ion filter part, said filter electrodes being separated and forming an analytical gap in said ion filter part, said flow path extending through said analytical gap, defining said analytical gap as well as the sides of said flow path in said ion filter part by cooperation of said support structure, said filter electrode support and said filter electrodes, providing a compensated asymmetric filter field within said analytical gap between said electrodes, separating at least one analyte chromatographically from a chemical mixture and eluting said separated analyte into said flow path, said analyte forming a chromatographic peak that is associated with a chromatographic residence time, said peak having a peak duration of some time period, providing a flow of ions to said ion filter part in said flow path within said time period, including the step of ionizing at least a portion of said separated at least one analyte and forming at least one ion species, further including flowing said at least one ion species into said flow of ions within said time period, providing said compensated asymmetric filter field transverse to said flow path in said ion filter part within said time period, filtering said flow of ions within said time period and selecting said at least one ion species out of said flow of ions, said selection being made according to aspects of ion mobility characteristics of said at least one ion species in said transverse field within said time period, and passing said selected at least one ion species to said output part within said time period for characterization of said at least one analyte according to mobility characteristics of said selected at least one ion species in said transverse field within said time period.

48. Method of claim 47 wherein said system further includes a housing for containing said ion filter and said internal flow path, further including the step of providing said filter with filter electrodes having inner faces facing each other across said flow path for forming said field, said facing electrodes having outer faces associated with said housing.

49. Method of claim 47 wherein said time period is about a second or less.

50. Method of claim 47 further comprising said the step of applying a drift gas to said eluted analyte to increase said flow volume and velocity of said ions through said system.

51. Method of claim 50 wherein said analyte is eluted from a capillary column of a gas chromatograph, further comprising said step of surrounding said capillary column outlet with said flowing drift gas.

52. Method of claim 51 further including the step of forming reactant ions in said flow of ions, said reactant ions reacting with said ionized sample to create reactant ion data peaks, further comprising said step of obtaining chromatographic retention time related to said analyte by monitoring fluctuation in intensity of said reactant ion data peaks.

53. Method of claim 52 further comprising steps of applying a high asymmetric RF field in said filter and detecting positive and negative ions simultaneously passing through said high RE field for identification of at least one ion species passed by said filter.

54. Method of claim 47 further comprising the step of collecting detection data and obtaining retention time, compensation voltage and detection intensity, and relating this data to a store of data to identify said detected species.

55. Apparatus for fast characterization of a chromatographic sample, comprising: an input part, an ion filter part for filtering ions in an electric filter field, an output part, and a flow path connecting said parts, said parts being supported by a support structure defined by cooperating substrates, said ion filter part including at least a pair of plate-type filter electrodes on said substrates in said ion filter part and forming conductive electrode surfaces, said substrates forming other supporting surfaces in said ion filter part that support said electrodes in said ion filter part, said electrodes separated from each other and defining an analytical gap in said ion filter part, said filter field being generated across said flow path in said gap, said filter electrodes providing a compensated asymmetric RF filter field within said gap, wherein surfaces of said gap in said ion filter part are cooperatively defined by said electrodes and said support structure, said input part for receiving a chromatographic eluent, said eluent including at least one analyte, said input part for delivering a flow of ions to said flow path, said flow of ions including at least one ion species associated with said analyte, said ion filter part filtering said flow of ions in said compensated asymmetric RF filter field in said gap, wherein said analyte is represented by a chromatographic peak flowing at a selected flow rate, said peak having a peak duration in said ion filter part, and wherein said ion filter part passes said selected at least one ion species to said output part within said peak duration for characterizing said at least one ion species within said peak duration according to aspects of ion mobility in the filter field.

56. Apparatus of claim 55 wherein said filter electrodes are formed as plates on said substrates, said substrates isolating said plates from each other, wherein said RF field is generated between said plates in said gap.

57. Apparatus of claim 56 wherein said flow path has walls in said ion filter part, wherein said plates extend along a portion of said walls and wherein said substrates extend along another portion of said walls in said ion filter part.

Description

BACKGROUND OF THE INVENTION

The present invention relates to spectrometry, and more particularly, to methodology and apparatus for the analysis of compounds by chromatography-high field asymmetric waveform ion mobility spectrometry.

There is a developing interest in making in situ measurements of chemicals present in complex mixtures at industrial or environmental venues. A fully functional chemical sensor system may incorporate a front end, e.g., a gas chromatography (GC) analyzer as a compound separator, and then a detector, i.e., a spectrometer.

Gas chromatography is a chemical compound separation method in which a discrete gas sample (composed of a mixture of chemical components) is introduced via a shutter arrangement into a GC column. Components of the introduced gas sample are partitioned between two phases: one phase is a stationary bed with a large surface area, and the other is a gas which percolates through the stationary bed. The sample is vaporized and carried by the mobile gas phase (the carrier gas) through the column. Samples partition (equilibrate) into the stationary (liquid) phase, based on their solubilities into the column coating at the given temperature. The components of the sample separate from one another based on their relative vapor pressures and affinities for the stationary bed, this process is called elution.

The heart of the chromatograph is the column; the first ones were metal tubes packed with inert supports on which stationary liquids were coated. Presently, the most popular columns are made of fused silica and are open tubes with capillary dimensions. The stationary liquid phase is coated on the inside surface of the capillary wall.

Compounds are discriminated by the time that they are retained in the GC column (the time from sample injection to the time the peak maximum appears). Chemical species are identified from a sample based on their retention time. The height of any one of these peaks indicates the intensity or concentration of the specific detected compound.

A carrier gas (e.g., helium, filtered air, nitrogen) flows continuously through the injection port, and the column. The flow rate of the carrier gas must be carefully controlled to ensure reproducible retention times and to minimize detector drift and noise. The sample is usually injected (often with a microsyringe) into a heated injection port where it is vaporized and carried into the column, often capillary columns 15 to 30 meters long are used but for fast GC they can be significantly shorter (less than 1 meter), coated on the inside with a thin (e.g., 0.2 micron) film of high boiling liquid (the stationary phase). The sample partitions between the mobile and stationary phases, and is separated into individual components based on relative solubility in the liquid phase and relative vapor pressures. After the column, the carrier gas and sample pass through a detector that typically measures the quantity of the sample, and produces an electrical signal representative thereof.

Certain components of high speed or portable GC analyzers have reached advanced stages of refinement. These include improved columns and injectors, and heaters that achieve precise temperature control of the column. Even so, detectors for portable gas chromatographs still suffer from relatively poor detection limits and sensitivity. In addition, GC analyzers combined with any of the conventional detectors--flame ionization detectors (FID), thermal conductivity detectors, or photo-ionization detectors--simply produce a signal indicating the presence of a compound eluted from the GC column. However, presence indication alone is often inadequate, and it is often desirable to obtain additional specific information that can enable unambiguous compound identification.

One approach to unambiguous compound identification employs a combination of instruments capable of providing an orthogonal set of information for each chromatographic peak. (The term orthogonal will be appreciated by those skilled in the art to mean data which enables multiple levels of reliable and accurate identification of a particular species, and uses a different property of the compound for identification.) One such combination of instruments is a GC attached to a mass spectrometer (MS). The mass spectrometer is generally considered one of the most definitive detectors for compound identification, as it generates a fingerprint pattern of fragment ions for each compound eluting from the GC. Use of the mass spectrometer as the detector dramatically increases the value of analytical separation provided by the GC. The combined GC-MS information, in most cases, is sufficient for unambiguous identification of the compound.

Unfortunately, the GC-MS is not well suited for small, low cost, fieldable instruments. Therefore there is still a strong need to be met with a fieldable chemical sensor that can generate reliable orthogonal information. A successful field instrument should include both a small injector/column and a small detector/spectrometer and yet be able to rapidly produce unambiguous orthogonal data for identification of a detected compound.

While GC's are continuously being miniaturized and reduced in cost, mass spectrometers are still very expensive, easily exceeding $100K. Their size remains relatively large, making them difficult to deploy in the field. Mass spectrometers also suffer from the need to operate at low pressures, and their spectra can be difficult to interpret often requiring a highly trained operator. The search therefore has continued for fieldable spectrometer.

Time-of-flight Ion Mobility Spectrometers (TOF-IMS) have been described as detectors for gas chromatographs from early in the development of ion mobility spectrometry and the first successful use of TOF-IMS detectors with capillary chromatography occurred in 1982. High-speed response and low memory effects were attained and the gas phase ion chemistry inside the TOF-IMS can be highly reproducible providing the foundation to glean chemical class information from mobility spectra. Thus, TOF-IMS, as ionization detectors for GC, do exhibit functional parallels to mass spectrometers, except all processes in IMS occur at ambient pressure making vacuum systems unnecessary. The IMS spectra is also simpler to interpret since it contains fewer peaks, due to less ion fragmentation. The usefulness of a gas chromatograph with TOF-IMS detector has been recognized for air quality monitoring, chemical agent monitoring, explosives detection, and for some environmental uses.

Fieldability still remains a problem for TOF-IMS. Despite advances over the past decade, TOF-IMS drift tubes are still comparatively large and expensive and suffer from losses in detection limits when made small. The search therefore still continues for a successful field instrument that includes both a small ion injector/column and a small detector/spectrometer and yet is able to rapidly produce unambiguous orthogonal data for identification of a detected compound.

The high field asymmetric waveform ion mobility spectrometer (FAIMS) is an alternative to the TOF-IMS. In a FAIMS device, a gas sample that contains a chemical compound is subjected to an ionization source. Ions from the ionized gas sample are drawn into an ion filter and subjected to a high field asymmetric waveform ion mobility filtering technique. Select ion species allowed through the filter are then passed to an ion detector, enabling indication of a selected species.

The FAIMS filtering technique involves passing ions in a carrier gas through strong electric fields between the filter electrodes. The fields are created by application of an asymmetric period voltage (typically along with a further control bias) to the filter electrodes.

The process achieves a filtering effect by accentuating differences in ion mobility. The asymmetric field alternates between a high and low field strength condition that causes the ions to move in response to the field according to their mobility. Typically the mobility in the high field differs from that of the low field. That mobility difference produces a net displacement of the ions as they travel in the gas flow through the filter. In absence of a compensating bias signal, the ions will hit one of the filter electrodes and will be neutralized. In the presence of a specific bias signal, a particular ion species will be returned toward the center of the flow path and will pass through the filter. The amount of change in mobility in response to the asymmetric field is compound-dependent. This permits separation of ions from each other according to their species, in the presence of an appropriately set bias.

In the past, Mine Safety Appliances Co. (MSA) made an attempt at a functional FAIMS implementation in a cylindrical device, such as disclosed in U.S. Pat. No. 5,420,424. (It is referred to by MSA as a Field Ion Spectrometer (FIS), see FIG. 1.) The device is complex, with many parts, and is somewhat limited in utility.

Fast detection is a sought-after feature of a Wieldable detection device. One characteristic of known FAIMS devices is the relatively slow detection time. However, the GC operates much more rapidly, such that the known FAIMS devices cannot generate a complete spectra of the ions present under each GC peak. Therefore these FAIMS devices would have to be limited to a single compound detection mode if coupled to a GC, with a response time of about 10 seconds. Any additional compound that is desired to be measured will take approximately an additional 10 seconds to measure.

While the foregoing arrangements are adequate for a number of applications, it is still desirable to have a small, fieldable ion detector/spectrometer that can render real-time or near real-time indications of detected chemical compounds, such as for use on a battlefield and in other environments.

Furthermore, a GC-FAIMS arrangement, focused as it is on one species at a time, is incapable of simultaneous detection of a broad range of species, such as would be useful for airport security detectors, or on a battlefield, or in industrial environments. Such equipment is also incapable of simultaneous detection of both positive and negative ions in a gas sample.

It is therefore an object of the present invention to provide a functional, small, fieldable ion detector/spectrometer that overcomes the limitations of the prior art.

It is a further object of the present invention to provide a chemical sensor that features the benefits of GC and FAIMS but is able to operate rapidly with reduced processing time.

It is a further object of the present invention to provide a chemical sensor that features the benefits of GC and FAIMS but is able to detect multiple species at one time.

It is a further object of the present invention to provide a chemical sensor that features the benefits of GC and FAIMS but is able to generate orthogonal data that fully identifies a detected species.

It is a further object of the present invention to provide a chemical sensor that features the benefits of GC and FAIMS but is able to detect positive and negative ions simultaneously.

It is a further object of the present invention to provide a fieldable chemical sensor that includes both a small ion injector/column and a small detector/spectrometer and yet is able to rapidly produce unambiguous orthogonal data for identification of a variety of chemical compounds in a sample.

It is a further object of the present invention to enable a new class of chemical sensors that can rapidly produce unambiguous, real-time or near real-time, in-situ, orthogonal data for identification of a wide range of chemical compounds.

It is a further object of the present invention to provide sensors that have the ability to detect both positive and negative ions simultaneously and achieving reduction of analysis time.

It is a further object of the present invention to provide a class of sensors that have the ability to use the reactant ion peak to extract the retention time data from a GC sample.

It is a further object of the present invention to provide a class of sensors that have the ability to make 2-D and 3-D displays of species information as obtained.

It is a further object of the present invention to provide a class of sensors that enable use of pattern recognition algorithms to extract species information. It is a further object of the present invention to provide a class of sensors that do not require consumables for ionization.

It is a further object of the present invention to provide a class of sensors that provide differential-mobility spectra information in addition to the retention time data.

It is a further object of the present invention to provide a class of sensors that can eliminate the need to run standards through the GC.

It is a further object of the present invention to provide a class of sensors utilizing arrays of FAIMS devices each tuned to detect a particular compound, such that multiple compounds can be simultaneously detected rapidly, with simplified electronics.

It is a further object of the present invention to provide a GC detector which detects compounds by ionizing eluted sample and uses different amplitudes of an applied high filed asymmetric waveform to produce different levels of ion clusters, which can be useful in more precise species identification.

It is a further object of the present invention to provide a class of sensors utilizing arrays of FAIMS devices to provide redundancy in ion detected.

It is a further object of the present invention to provide a class of sensors utilizing arrays of FAIMS devices where each ion filter has its own flow path (or flow channel) and is doped with a different dopant for better compound identification.

It is a further object of the present invention to provide a class of sensors utilizing arrays of FAIMS devices each swept over an assigned bias range of the spectrum to obtain faster analysis of the contents of an eluted GC peak.

It is a further object of the present invention to provide a class of detectors that can provide information on the cluster state of ions and ion kinetics by varying the amplitude of the high voltage asymmetric electric field or by adjusting the flow rate of ions through the device.

It is a further object of the present invention to provide a chemical sensor that features the benefits of GC and FAIMS but is able to detect positive and negative ions simultaneously by providing a longitudinal flow path in which positive and negative ions are carried simultaneously through the filter to the detector for simultaneous independent detection.

It is a further object of the present invention to provide a class of sensors that can detect samples over a wide range of concentrations through a controlled dilution of the amount of sample delivered to the PFAIMS through appropriate control of the ratios the amounts of drift, carrier and sample gasses.

It is further an object of this invention to provide a class of sensors that can quantitatively detect samples over a wide range of concentrations through controlled dilution by regulating the amount of ions injected into the ion filter region by controlling the potentials on deflector electrodes.

SUMMARY OF THE INVENTION

These and other objects are well met by the presently disclosed invention. The present invention overcomes cost, size or performance limitations of MS, TOF-IMS, FAIMS, FIS and other prior art devices, in a novel method and apparatus for chemical species discrimination based on differences in ion mobility in a compact, fieldable package.

In one aspect of the invention, a portable chemical sensor is provided. In another aspect of the invention, improvements in laboratory equipment for substance identific