System for trajectory-based ion species identification Number:7,148,477 from the United States Patent and Trademark Office (PTO) owispatent Method and apparatus for field ion mobility spectrometry for identification of chemical compounds in a sample by trajectory of sample ions in a transverse electric field.<H identification, trajectory, System, for, traj, 7148477.html, Patent, pto, 7148477

Title: System for trajectory-based ion species identification

Abstract: Method and apparatus for field ion mobility spectrometry for identification of chemical compounds in a sample by trajectory of sample ions in a transverse electric field.

Patent Number: 7,148,477 Issued on 12/12/2006 to Miller, et al.

Inventors: Miller; Raanan A. (Newton, MA), Nazarov; Erkinjon G. (Lexington, MA), Kaufman; Lawrence A. (Waltham, MA)
Assignee: Sionex Corporation (Bedford, MA)

Appl. No.: 10/840,829

Filed: May 7, 2004

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
10278738	Oct., 2002
10187464	Jun., 2002	7045776
09896536	Jun., 2001
10321822	Dec., 2002	6806463
09358312	Jul., 1999	6495823
10082803	Feb., 2002	6815669
09439543	Nov., 1999	6512224
09358312	Jul., 1999	6495823
60336522	Oct., 2001
60336506	Oct., 2001
60351043	Jan., 2002
60334685	Nov., 2001
60340894	Oct., 2001

Current U.S. Class: 250/294 ; 250/282; 250/293

Current International Class: B01D 59/44 (20060101); H01J 49/00 (20060101); H01J 49/28 (20060101)

Field of Search: 250/290-294,282

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Primary Examiner: Berman; Jack
Assistant Examiner: Yantorno; Jennifer
Attorney, Agent or Firm: Fish & Neave IP Group, Ropes & Gray LLP

Parent Case Text

CROSS REFERENCE OF RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 10/278,738, filed Oct. 22, 2002, now abandoned which is a continuation-in-part of U.S. application Ser. No. 10/187,464, filed Jun. 28, 2002, now U.S. Pat. No. 7,045,776 which is a continuation-in-part of U.S. application Ser. No. 09/896,536, filed Jun. 30, 2001, now abandoned and which claims the benefit of U.S. Provisional Application No. 60/340,894, filed Oct. 30, 2001, U.S. Provisional Application No. 60/334,685, filed Nov. 15, 2001, U.S. Provisional Application No. 60/351,043, filed Jan. 23, 2002, and also claims the benefit of U.S. Provisional Application No. 60/336,506, filed Oct. 23, 2001, and U.S. Provisional Application No. 60/336,522, filed Oct. 23, 2001.

This application is a continuation-in-part of U.S. application Ser. No. 10/321,822, filed Dec. 16, 2002, now U.S. Pat. No. 6,806,463 which is a continuation of U.S. application Ser. No. 09/358,312, filed Jul. 21, 1999 (now issued U.S. Pat. No. 6,495,823, issued Dec. 17, 2002).

This application is also a continuation-in-part of U.S. application Ser. No. 10/082,803, filed Feb. 21, 2002, now U.S. Pat. No. 6,815,669 which is a continuation-in-part of U.S. application Ser. No. 09/439,543, filed Nov. 12, 1999 (now issued U.S. Pat. No. 6,512,224, issued Jan. 28, 2003), which is a continuation-in-part of the above U.S. application Ser. No. 09/358,312.

The entire contents of all of the above applications are incorporated herein by reference in their entirety.

Claims

What is claimed is:

1. A field ion mobility analytical system comprising: a pair of electrode banks defining between them a flow path, an ion separator and an ion detector, said separator and said detector for making trajectory-based ion species identification of ions flowing in said flow path between said banks, said electrodes being separated by an analytical gap, each said bank comprising at least one separator electrode for forming said ion separator, at least one said bank having a plurality of electrodes, at least one of said plurality of electrodes comprising a detector electrode, an electrical controller input for applying a time-varying voltage to said ion separator and generating a transverse time-varying electric field between said separator electrodes while the ions are flowing along the flow path for controlling the paths of said ions in said separator, said field causing selected ions of said flow of ions to contact said detector electrode based on ion mobility in the field and consequent ion trajectory, said ions contacting said detector being identifiable based at least in part on said trajectory.

2. System of claim 1 further comprising an analytical package, said package forming said ion separator, said ion detector and said banks associated with said flow path.

3. System of claim 2 wherein said banks are spaced apart forming an analytical gap.

4. System of claim 3 wherein said gap is about 0.5 mm between facing electrodes on said banks.

5. System of claim 1 wherein said plurality of electrodes comprises a plurality of detector electrodes.

6. System of claim 1 further comprising at least one low noise amplifier, wherein said detection at said detector electrode is communicated to said controller via said amplifier.

7. System of claim 1 wherein said electrodes form an integrated ion filter-detector for simultaneous detection of distinct species of ions based on their trajectory according to their mobility in said asymmetric field, and wherein said field includes a RF field.

8. System of claim 1 further comprising a detector downstream from said banks for detecting ions that exit said separator.

9. System of claim 1 wherein said detector includes a plurality of segments, said segments separated along said flow path to spatially detect said ions according to their trajectories.

10. A high field ion mobility spectrometer for analysis of compounds in a sample, comprising: a source of charged ions representative of compounds in a sample, an ion flow path, a plurality of electrodes forming banks along said flow path, said banks facing each other over said flow path down stream from said source, said charged ions flowing between said banks in said flow path, each said bank including at least one filter electrode, a controller input for application of time-varying voltages to said filter electrodes for inducing a time-varying electric field between said filter electrodes while the ions are flowing along the flow path, said charged ions being subjected to said field between said banks, said field imparting a respective trajectory to a respective charged ion according to ion mobility characteristics of said respective charged ion, and at least one of said banks defining at least one detector electrode, said detector electrode for receipt of charge deposits from species of said charged ions having common trajectories.

11. The spectrometer of claim 10 wherein said at least one of said banks having said at least one detector electrode comprises a multi-function bank of electrodes and faces the other said bank across said flow path.

12. The spectrometer of claim 11 wherein said multi-function bank comprises an array of filter electrodes, wherein one of said filter electrodes is also said detector electrode.

13. The spectrometer of claim 11 wherein said multi-function bank comprises an array of filter electrodes, wherein said filter electrodes are detector electrodes.

14. The spectrometer of claim 11 wherein said multi-function bank comprises an array of detector electrodes, wherein said array of detector electrodes is formed interspersed with said filter electrodes.

15. The spectrometer of claim 10 wherein said mobility characteristics are based on ion features including size, charge, and cross-section of said charged ions.

16. The spectrometer of claim 10 wherein said ions are carried in a carrier gas in said flow path.

17. The spectrometer of claim 10 wherein said ions are electrically propelled in said flow path.

18. The spectrometer of claim 11 wherein said multi-function bank comprises an array of detector electrodes, wherein said array includes said at least one detector electrode, said controller enabling simultaneous detection of ion species on a respective one of said detector electrodes based on differences in trajectory.

19. The spectrometer of claim 10 wherein said electrodes form an integrated ion filter-detector for simultaneous detection of distinct species of ions based on their trajectory according to their mobility in said time-varying field.

20. Method for identification of a chemical in a sample, comprising the steps of: i) ionizing the sample, ii) flowing the sample as a flow of ions along a flow path between a series of electrodes, iii) providing a time-varying electric field between said electrodes while the ions are flowing along the flow path and generating mobility behavior of said ions, iv) separating said ions according to species, said separation based on said behavior in said field as expressing mobility characteristics of said species, and v) providing an ion separator and an ion detector, said separator and said detector including a plurality of electrodes in said series of electrodes, for making trajectory-based ion species identification.

21. Method of claim 20 further comprising the step of applying at least one high voltage to said ion separator and generating a transverse high electric field between said separator electrodes for controlling the paths of said ions in said separator, said field causing selected ions of said flow of ions to contact said detector electrode based on ion mobility in the high field and consequent ion trajectory, and said selected ions forming an ion species defined as having the same ion mobility and said selected ions contacting said detector electrode at said flow rate.

22. Method of claim 20 comprising identifying ion species based on a carrier flow rate and field conditions.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to identification of unknown members of a sample by mobility characteristics, and more particularly to devices that analyze compounds via field-based ion mobility spectrometry.

There are a number of different circumstances in which it is desirable to perform a chemical analysis to identify compounds in a sample. Such samples may be taken directly from the environment or they may be provided by specialized front-end devices that separate or prepare compounds before analysis.

Furthermore, recent events have seen members of the general public exposed to dangerous chemical compounds in situations where previously no thought was given to such exposure. There exists, therefore, a demand for accurate, easy to use, and reliable devices capable of detecting the chemical makeup of a sample rapidly and even at trace levels, whether in the laboratory or in the field.

Mass spectrometers are generally recognized as highly accurate detectors for compound identification, given that they can generate a fingerprint pattern for even fragment ions. However, mass spectrometers are quite expensive, easily exceeding a cost of $100,000 or more and are physically large enough to become difficult to deploy everywhere the public might be exposed to dangerous chemicals. Mass spectrometers also suffer from other shortcomings such as the need to operate at relatively low pressures, resulting in complex support systems. They also need a highly trained operator to tend to and interpret the results. Accordingly, mass spectrometers are generally difficult to use outside of laboratories.

A class of chemical analysis instruments more suitable for field operation operate based upon aspects of ion mobility in an analytical field. One such type is known as Field Asymmetric Ion Mobility Spectrometers (FAIMS) (also known as Radio Frequency Ion Mobility Spectrometers (RFIMS) and Differential Mobility Spectrometers (DMS), among other names. This type of spectrometer subjects an ionized sample to a compensated varying high-low asymmetric electric field and filters ions based on aspects of their field mobility.

Typically a gas sample flows through a varying high asymmetric RF field which allows only selected ion species to pass through, according to an applied low DC compensation voltage, and specifically only those ions that exhibit selected mobility responses in the field. An ion detector then collects detection data for the detected ions. This may include intensity data shown as detection "peaks." These peaks are interpreted according to the compensation voltage at which a species of ion is able to pass through an asymmetric field of given field parameters.

A typical FAIMS device includes a pair of electrodes in a drift tube. An asymmetric field is applied to the electrodes transverse to the ion flow path. The asymmetric RF field alternates between a high or "peak" field strength and a low field strength. The field varies with a particular frequency and duty cycle. Field strength varies as the applied voltage and size of the analytical gap between the electrodes.

In a FAIMS device, ions will pass through the analytical gap between the electrodes only when their net transverse displacement per period of the asymmetric field is zero; in contrast, ions that undergo a net displacement will eventually undergo collisional neutralization on one of the electrodes. In a given RF asymmetric field, a displaced ion can be restored to the center of the gap (i.e. compensated, with no net displacement for that ion) when a low strength DC electric field (the compensation voltage, Vcomp) is superimposed on the RF. Ions with differing displacement (owing to characteristic dependence of mobility in the field) can be passed through the gap at compensation voltages characteristic of a particular ion, which is accomplished by applying various strengths of Vcomp. With Vcomp held at one value, the system can function as a continuous ion filter, or a scan of Vcomp will allow complete measure of the spectrum of ion species in the sample. The recorded image of the spectral scan of the sample is sometimes referred to as a "mobility scan" or as an "ionogram".

The detected compounds can be identified by comparing detection data against a library, for example, of stored known identification data. By noting the RF level and compensation voltage and the corresponding detected signal, an ion species can be identified, as well as concentration level (as seen in the detection peak characteristics). Ideally a specific RF level and compensation voltage will permit only a particular species of ion (according to signature mobility in the field) to pass through the filter to the detector. However, if mobilities overlap under the selected field conditions, then the detected species may contain ions for several compounds happening to have the same mobility under those conditions. This can result in detection errors, sometimes referred to as "false positives".

It is an object of the invention to provide a simple and compact apparatus to achieve such detections with improved accuracy.

It is another object of the invention to provide an improved ion species detection device with higher sensitivity and reduced false positives.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will be more fully understood by reference to the following detailed description of illustrative embodiments of the invention in conjunction with the attached drawing in which like reference numerals refer to like elements and in which:

FIG. 1 is a schematic of a high field asymmetric ion mobility chemical analysis system;

FIG. 2 is a schematic of an illustrative embodiment of the present invention.

FIG. 3A is a schematic of the separator-detector of the embodiment of FIG. 2 in practice of the invention; and

FIGS. 3B and 3C are alternative electrode configurations of the embodiment of FIG. 3A, each with two multi-function electrode sets (or "banks"), in practice of the invention.

SUMMARY OF THE INVENTION

The present invention is directed to an ion separator and detector that separates and detects ion species, configured in a compact package. Ion separation is based on ion mobility in a separation electric field. Embodiments of the present invention may operate with low and/or high RF or DC separation fields.

The present invention has application to FAIMS high field ion mobility spectrometry, which features selective neutralization of ion species. It also includes the recognition that improved identification or discrimination of compounds may be achieved by other use of ion neutralizations in the ion analysis process. In one embodiment, the present invention provides a high field ion mobility method and apparatus for separation and detection of ion species in a chemical sample. In another practice the present invention provides a trajectory-based field ion mobility method and apparatus. These modes may be used singly or together.

In an illustration of this embodiment, an ion separator-detector separates and detects an ion species based on ion trajectory when subjected to a transverse separator field. The field is created in an analytical gap separating two electrode banks within the separator-detector. The ions are transversely driven by the separator field in the gap. The ions are neutralized by contact with electrodes of the electrode banks. Any ions contacting the same electrode are of a common mobility species that is defined by their trajectory in the field. At least one of these electrodes serves as a detector electrode and species are detected based upon this contact. Thus separation and detection are both achieved in a single analytical space (the analytical gap between the separator banks of the separator-detector). The detection data can be processed and compared to a lookup table to identify the detected species.

It is significant that the ion separator performs trajectory-based separation of ion species by applying a transverse separation field in the separator, and that detection of these separated species occurs within that same separator-detector space based upon the trajectory of the ion species in the field. No additional detector arrangement is required, and a compact and efficient chemical analyzer is provided. One advantage of this arrangement is that separation and detection can be obtained all within a single simple electrode bank structure. Multiple processing environments and data comparisons are not required. One other advantage is that using multiple electrodes in the electrode banks enables simultaneous detection of multiple ion species. This provides for a fast device with high throughput.

In an alternative compact device of the invention, the detector is downstream of the analytical gap and detection continues based on trajectory aspects of the separated ion flow. The detector can be a series of segments in the downstream flow path. An advantage of this configuration is separation of the detector from influence of the filter field, which may be desired.

The present invention has application to FAIMS high field ion mobility spectrometry and includes the recognition that improved identification or discrimination of compounds may be achieved by more complete and innovative use of ion neutralizations in the ion analysis process. In one embodiment, the present invention provides a high field ion mobility method and apparatus for separation and detection of ion species in a chemical sample. In another practice, the present invention provides a field ion mobility method and apparatus for simultaneous separation and detection of multiple ion species in a complex chemical sample. Yet other embodiments are also provided. Embodiments of the invention include gas-driven or field-driven ion transport.

The present invention makes possible rapid identification of a wide range of compounds, including compounds that are difficult to identify by conventional means. This field ion mobility spectrometer can perform substantive quantitative analysis of complex mixtures in essentially real-time. (For purposes of this disclosure the concepts of "rapid" or "fast" may also be referred to as "real-time" or "near real-time"; while these are relative terms, detection within a fraction of a second or even within a second or a few seconds is certainly contemplated within these concepts and will be understood as being within the scope of the invention.)

In one embodiment, a bank or banks (i.e., a set or sets) of electrodes are formed along an ion flow path (i.e., flowing in a drift tube), and the electrodes interact to form an integrated ion separator-detector. At least a pair of opposed electrodes form separator electrodes between which the separation field is formed. At least one electrode is a detector electrode. In a multiple electrode embodiment, the separator-detector enables separation and detection, preferably simultaneously, of a plurality of distinct species of ions in a chemical mixture based on trajectory of the ions according to their mobility differences in the high field.

In an illustration of the invention, the separator electrodes face each other over the ion flow path, and at least one of the banks also has at least one detector electrode. The at least one detector electrode may be one of the separator electrodes or may be a separate electrode adjacent to a separator electrode. Preferably this all occurs in the ion separation region in the analytical gap formed between multiple separator electrodes. (The separator is a filter. The separator-detector may also be referred to as a filter-detector. The separator field may also be referred to as a filter field.)

In one preferred embodiment, multiple electrodes are provided on each bank. Each of these banks has a plurality of electrically isolated separator electrodes and these electrodes also function as detector electrodes. In another embodiment, detector electrodes are interspersed with the separator electrodes in a bank or banks of electrodes. In an embodiment of the invention, all of the electrodes of the banks can be independently accessed and controlled.

A preferred apparatus includes a source of charged ions, representing compounds in a sample to be analyzed, a housing defining an ion flow path (i.e., a drift tube) and a plurality of electrodes forming electrode banks along the flow path. Each bank includes at least one separator electrode, preferably multiple separator electrodes, with these electrodes facing each other over the flow path downstream from the ion source. The charged ions flow between the electrode banks in the flow path. One of the banks further includes at least one detector electrode, and preferably there are a plurality of detector electrodes, wherein the detector electrodes are for detection of ions according to their trajectories in the field.

A controller is provided for application of drive voltages to the separator electrodes for inducing the electric field in the analytical gap between the separator electrodes. The charged ions are subjected to the field, and the field imparts a respective trajectory to a respective charged ion according to ion mobility characteristics of the ions, which reflects the field effect and the ion flow rate in the filter field. Preferably the field is high (e.g., at or above 5000 v/cm.sup.2). In one illustrative practice, a high field was formed in a 0.5 mil analytical gap separating the separator electrodes; the RF maximum voltage was operated at about 1500v-p-p.

In a preferred embodiment, a bank of electrodes includes a plurality of multi-use separator electrodes. These multi-use electrodes provide the separator field of the invention and also can be monitored for ion neutralizations; in this latter sense they perform the function of detector electrodes. This multi-function bank preferably is mounted facing a second bank across the flow path, with the separator field generated between these banks. In an alternative embodiment, separator and detector electrodes in the electrode bank are interspersed and as a team perform the multiple functions of separating and detecting. Thus the electrode banks are multi-functional.

In one embodiment, a set of electrodes performs both separator and detector functions simultaneously, and multiple species of ions are separated and detected simultaneously. In another embodiment, separator electrodes are interspersed with detector electrodes, and still multiple species of ions can be separated and detected simultaneously. In any case, in a preferred embodiment of the invention, each of the electrodes performing a detection function is coupled to a respective narrow bandwidth amplifier. Each of these amplifiers can be tune to a particular field condition, wherein each can be focused on detection of a particular ion species of interest.

The result of using such narrowband amplifiers is relatively low noise in the detection process and relatively high detection sensitivity, such as compared to prior art conventional FAIMS. In practice of the invention, conventional wider bandwidth amplifiers could be used where each detector needs to be able to scan a full spectrum. This would be a general purpose application of the invention.

However, since embodiments of the present invention enable each detector to be dedicated to a narrow range of interest (in view of its physical location along the flow path and its trajectory-based detection function) the ability to scan a complete spectrum of compounds (i.e., associated with a wide range of compensation voltages) in the sample is not needed. This would be a dedicated use application of the invention, and would enable a fast response system.

In embodiments of the present invention, the ions are propelled in the flow path by control of ion flow, such as control of a carrier gas transport, for example. Further embodiments of the invention include electrodes formed on spaced-apart substrates that define the enclosed internal flow path between the electrodes. The result is a light-weight and compact spectrometer with high sensitivity and capable of real-time analysis of a complex chemical sample.

In a preferred practice of the invention, the ionized sample may include both positive and negative ions which are carried to the separator. This is significant because an ion species may include both positive and negative ions. A preferred analysis may include evaluation of both modes. In a preferred embodiment of the invention, the separator-detector detects both positive and negative ions simultaneously, according to trajectory. This extra information provides improved and rapid species identification with low false positives.

The present invention may be practiced in several modes. It may be operated as a trajectory-based ion separator, with or as a FAIMS device, or with or as a hybrid trajectory-FAIMS-based separator-detector. Separations and detections may be made in any one or any combination of these modes.

In one practice of the present invention, a spectrometer is capable of identification of numerous compounds simultaneously without the need for the compensation or scanning of conventional FAIMS. This embodiment features at least one high field ion mobility separator-detector electrode bank, where the electrode bank is multi-functional and separating proceeds based on ion trajectory in the analytical gap between the electrode banks. For a flow of ions traveling at a given flow rate, the trajectory of a particular ion in that flow, as it is subjected to the high field transverse to the ion flow, is a function of ion size, cross-section, charge and mass. This function is generally referred to as high-field mobility.

Generally speaking, a particular ion species will have a unique field mobility, which can be determined as a "mobility signature". We have found in FAIMS systems that an expression of the high field-dependence of ion mobility, the so-called alpha coefficient, expressed as a function of field, can be used to generate a unique alpha function that is inherent for that species: its unique high-field mobility signature. This function expresses a characteristic signature for the ion species. This detection and identification strategy is set forth in detail in our copending application Ser. No. 10/187,464, filed Jun. 28, 2002, incorporated herein by reference. These signatures may be used as part of or to supplement species identification in practice of the invention. The signature can be determined for a detected unknown compound based on the high field conditions that are used, and then this can be used to make an identification according to a lookup table of stored known signature data associated, or by other known identification techniques.

In an illustrative FAIMS application of the alpha function, ion species are identified based on the mobility dependence of the species under various field conditions. For any given set of field conditions, the field strength and compensation can be correlated with an alpha value. Since field strength and compensation value are known at the time that a detection is made, and the alpha can be determined, then lookup of the species associated with that alpha enables precise species identification.

In practice of the present invention, an ion species is identified based on its field mobility signature. In one embodiment, a DC voltage is applied to a first separator electrode on one bank with an opposed electrode on the opposed bank being at ground, the electrodes being separated by an analytical gap of 0.5 mm. In another embodiment the DC is floating between the electrodes and is pulsed. In one embodiment, a high DC field is presented between these electrodes and mobility difference behavior of the ions in this field can be detected as set forth herein.

In another embodiment, an asymmetric RF voltage applied to the ion separator electrodes in the range of about 900 to about 1.5 kV (high field condition), followed by a low voltage of about -400 to -500 V (low field condition). The system analytical gap separating the electrodes was 0.5 mm. Other embodiments are also within the scope of the invention.

In any event, it will be appreciated that the ability to perform a variety of high field analytical events on a sample or samples enables the collection of substantial species-specific detection data. The result is more accurate identifications with fewer false positives.

Systems of the invention can be switched between various modes of operation. In one embodiment, in a trajectory mode, ions are separated based on differences in field mobility behavior and on trajectory as they deposit their charges on detector electrodes of the separator-detector array or on downstream detector electrodes, which may be a bank of detector electrodes. The field may be DC or RF, low or high. Preferably ions are neutralized as they hit an electrode; wherein an ion species will be neutralized on a particular detector electrode according to ion trajectory in the field, and according to the ion transport flow rate. The ion species can be identified thereby.

In one embodiment of a switchable system of the invention, we can operate in an ion-mobility based mode (FAIMS or even conventional IMS) mode or in an uncompensated field mode. Ions are separated based on differences in field mobility behavior and are detected upon depositing their charges on detector electrode(s). The separation is ion mobility based and may include the benefit of trajectory affects.

The detection data is processed and an indication of presence of the ion species can be made, such as by illuminating a red light in a dedicated system. In another system an identification of various compounds in the sample can be made even where the system is not dedicated to a specific ion species detection. In a preferred embodiment, species identification is by the high field mobility parameter (alpha).

There are several modes of operation of the invention for sample characterization. As an illustration, for a given sample to be analyzed, one mode of operation may be adjusted to provide a first set of detection data for a first set of conditions while a second mode of operation may be adjusted to provide a second set of detection data for the same or for a second set of conditions. For example, high field trajectory-based detection might be used to detect isomers of a compound while the FAIMS mode might be used to detect monomers of a compound in a sample, or vice versa, according to the character of the target (suspected) analytes of interest. Combination of resulting detection data enables rapid characterization of the components in a chemical sample with a high degree of confidence.

These and other innovations of the invention will be appreciated by a person skilled in the art by reference to the specification set forth below.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A FAIMS spectrometer 10, shown in FIG. 1, receives a chemical sample 12 at inlet 14. The sample flows into ionization region 16 in flow path 18, where it is ionized by ionization source 20. Ionization of the compounds in the sample creates ionized molecules ("ions") that are carried by a transport or carrier medium into the ion filter 22 in flow path 18 between filter electrodes 24, 26. Embodiments of a compact and efficient high field asymmetric ion mobility spectrometer are disclosed in U.S. Pat. No. 6,495,823 (ion transport by carrier gas) and in U.S. Pat. No. 6,512,224 (electric field ion transport), incorporated herein by reference. Systems of the invention may include plate type or cylindrical type electrodes and the like.

A compensated, asymmetric high electric field is generated between the filter electrodes that has differential impact upon mobility of the ions according to their size, charge and cross-section, and mass. This mobility difference produces a characteristic net transverse displacement of the ions as they travel longitudinally through filter 22 between the filter electrodes 24, 26.

The transverse displacement results in ions driving into the filter electrodes and being neutralized. However, in the presence of a low voltage DC compensation bias applied to the field, a particular ion species 12' will be returned toward the center of the flow path and will pass through the filter to be detected on electrodes 28 or 30 of detector 32. While ion species 12' is returned toward the center of the flow path and passes through the filter to detector 32, all other species 12'' will not be sufficiently compensated and will collide with the filter electrodes and will be neutralized. This elimination of ion species by neutralization is an essential part of conventional high field asymmetric ion mobility isolation of an ion species of interest. The latter is passed by the ion filter unneutralized for downstream detection.

Each detector is preferably supported by an amplifier 28a, 30a, wherein the signal generated by the ions depositing their charges on the detector electrodes will be amplified and delivered to the system controller for processing. The detection signal indicates the presence of a detected target ion species. Such detection event is correlated with the RF field conditions and DC compensation level and which is matched with a table of data associated with known species for identification of the detected species. Preferably the identification is based on the high field mobility of the detected species as expressed in its associated alpha function. Furthermore, the detection signal intensity relates to the quantity of detected ion species. Therefore this method is both qualitative and quantitative.

If multiple compounds are in the sample, then multiple tests may be run, in sequence, each with an appropriate compensation level, or else a scan can be run through different compensation levels. By sweeping the compensation over a predetermined voltage range, a spectrum can be analyzed, one step after another, to cover a range of mobilities to detect various compounds that may be in the sample.

The above FAIMS spectrometer is adequate for real-time analysis in many applications. However, for a given set of field conditions and compensation level, it is possible that ions representing multiple species may be passed to the detector. It is desirable to apply additional strategies for a compact spectrometer that can render real-time detection of multiple chemical compounds simultaneously with minimal false positives.

Therefore, one embodiment of the present invention is directed to an ion separator and detector that separates and detects ion species in a compact package. In one embodiment this package may also be operated as a FAIMS detector. This system may operate with low and/or high RF or DC fields.

In an illustration of this embodiment, an ion separator-detector separates and detects an ion species based on ion trajectory when subjected to a transverse separator field. The field is created in an analytical gap separating two electrode banks within the separator-detector. The ions are transversely driven by the separator field in the gap. The ions are neutralized by contact with electrodes of the electrode banks. Any ions contacting the same electrode are of a common mobility species that is defined by their trajectory in the field. At least one of these electrodes serves as a detector electrode and species are detected based upon this contact. Thus separation and detection are both achieved in a single analytical space (the analytical gap between the separator banks of the separator-detector). AS will be appreciated by a person skilled in the art, the detection data can be processed and compared to a lookup table to identify the detected species, with knowledge of the ionization function, applied field, flow rate, pressure, humidity, etc.

In a preferred compact package of the invention, the ion separator performs trajectory-based separation of ion species by applying a transverse separation field in the separator, and detection of these separated species occurs within that same separator-detector space based upon the trajectory of the ion species in the field. No addition detector arrangement is required, and thus a compact and efficient chemical analyzer is provided.

One advantage of this arrangement is that separation and detection can be obtained all within a single simple electrode bank structure. Multiple processing environments and data comparisons can be used but are not required. One other advantage is that using multiple electrodes in the electrode banks enables simultaneous detection of multiple ion species by trajectory. This provides for a fast device with high throughput.

Referring again to the device of FIG. 1, it will be appreciated that we can obtain detection data by monitoring ion deposits (neutralizations) at detectors 28, 30. Amplifiers 28a, 30a, couple the detector electrodes to the controller for collection of this detection data. Optionally, we also can monitor ion neutralizations at separator electrodes 24, 26, and optional amplifiers 24a, 26a (shown added in dotted outline) may also be provided for collection of the ion neutralization data at separator electrodes 24, 26. The result is more complete detection data for enhanced chemical identification.

One limitation with the ion neutralization data collected at separator electrodes 24, 26, is that there is rela