WO2004097396A1 - Apparatus and method for controlling ion behavior in ion mobility spectrometry - Google Patents

Abstract

Method and apparatus are provided for controlling ion behavior in an ionbased analysis system. The system for controlling ion behavior in an ion-based analysis system includes an ion source, an ion filter including electrodes separated by an analytical gap for generating an ion filter field, and an arrangement for controlling ion behavior in the flow path, wherein ions are separated according to species based on ion-mobility-based behavior in the field. In one embodiment charge dissipative surfaces in the flow path prevent charge buildup that otherwise can impact ion behavior. In another embodiment of the present invention, electronic control of ion behavior for optimization of mobility-based ion species filtering and control are implemented. A structure of partially conducting control material supporting a plurality of control electrodes is formed. These supported control electrodes are laid out as an addressable array.

Description

APPARATUS AND METHOD FOR CONTROLLING ION BEHAVIOUR IN ION MOBILITY SPECTROMETRY

FIELD OF THE INVENTION

This invention relates to methods and apparatus for detecting ions based on aspects of ion mobility behavior.

RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority to U.S. Application No. 10/462,206, filed June 13, 2003, and claims the benefit of U.S. Provisional Application No. 60/464,977, filed on April 24, 2003 and U.S. Provisional Application No. 60/483,001, filed on June 27, 2003 and U.S. Provisional Application No. 60/468,306, filed May 6, 2003, and U.S. Provisional Application No. 60/491,443, filed on July 31, 2003, and U.S. Provisional Application No. 60/504,024, filed on September 20, 2003. The entire teachings of the above application(s) are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Several approaches to chemical identification are based on the recognition that ion species have different ion mobility characteristics under different electric field conditions at atmospheric pressure. These approaches include conventional time-of- flight Ion Mobility Spectrometry (IMS) and conventional differential mobility spectrometry (DMS), the latter also known by other names such as field asymmetric ion mobility spectrometry (FAIMS). Atmospheric-pressure chemical ionization enables these identification processes (including radioactive, ultraviolet and electrospray ionization, for example). In a conventional IMS device, a weak DC field gradient is established between an upstream electrode and a downstream collector electrode and then an ionized sample is released into the DC field. The ionized sample flows toward the collector electrode. Ion species are identified based on the time of flight of the ions to the collector. The DC field is weak where ion mobility is constant.

A typical DMS device includes a pair of opposed filter electrodes defining an analytical gap between them in a flow path (also known as a drift tube or flow channel). Ions flow into the analytical gap. A compensated high-low varying asymmetric RF field (sometimes referred to as a filter field, a dispersion field or a separation field) is generated between the electrodes transverse the ion flow in the gap. Field strength varies as the applied RF voltage (sometimes referred to as dispersion voltage, separation voltage, or RF voltage) and size of the gap between the electrodes. Such systems operate at atmospheric pressure.

Ions are displaced transversely by the DMS filter field, with a given species being displaced a characteristic amount transversely toward the electrodes per cycle. DC compensation is applied to the electrodes to compensate or offset the transverse displacement generated by the applied RF for a selected ion species. The result is zero or near-zero net transverse displacement for that species, which enables that species to pass through the filter for downstream processing such as detection and identification. All other ions undergo a net transverse displacement toward the filter electrodes and will eventually undergo collisional neutralization on one of the electrodes.

If the compensation voltage is scanned for a given RF field, a complete spectrum of ion species in the sample can be produced. The recorded image of this spectral scan is sometimes referred to as a "mobility scan" or as an "ionogram". The time required to complete a scan is system dependent. Relatively speaking, a prior art IMS scan might take on the order of a second to complete while a prior art DMS might take on the order of 10 seconds to complete. DMS operates based on the fact that an ion species will have an identifying combination of high and low field mobility in the analytical RF field. DMS detects differences in such ion mobility between high and low field conditions and classifies ions according to these differences. These differences reflect ion properties such as charge, size, and mass as well as the collision frequency and energy obtained by ions between collisions.

It is therefore an object of the present invention to provide a fast and simple apparatus capable of high degree of species discrimination and accurate species identification for chemical analysis.

It is another object of the present invention to provide a high level of ion control to optimize ion filtering, detection and/or species identification in a system based on aspects of ion mobility.

SUMMARY OF THE INVENTION

Embodiments of the present invention, whether method or apparatus, perform a function wherein an ionized sample is processed in an ion flow path of a chemical analyzer. This processing at least includes either ion filtering or ion separating and preferably also includes ion species detection and identification.

The present invention is based on the recognition that ion behavior within the flow path of an ion-based chemical analysis device can be favorably controlled and manipulated to optimize system performance. In the invention, an influencing structure or influencing field influences the analytical environment within the analyzer with favorable results. This influencing governs ion flow to influence, counteract or overcome various local effects that impact ion behavior in the analytical field. Practices of the invention enable focusing, trapping, confining, translating, selecting, steering, filtering, even detecting of ions, and preferably in the flow path of an ion mobility-based analytical system such as an IMS or DMS system. In a preferred embodiment, the invention is integrated into a DMS system, which may be a spectrometer, filter, detector, separator, assembly, apparatus or the like. A flow path is defined that enables ionized sample to flow into the analytical gap defined between facing DMS filter electrodes in the flow path. Ion species are separated in the filter field and selected species are passed for downstream processing, such as for detection and identification, according to ion behavior in the compensated asymmetric RF filter field in the analytical gap between. Ion control is exercised within such devices of the invention and may be passive or active.

In several embodiments, we implement static or dynamic control of an electric field via a control structure to improve ion behavior within the analytical device. Use of this control structure may be with or without additional control elements. In one embodiment, a control material in the flow path of a DMS provides charge dissipating surfaces or structures that prevent charge buildup as would otherwise undesirably impact on ion behavior in the system. This material provides a discharge path for charges deposited on such surfaces, drawing the charges away from the flow path to prevent interference with the intended ion analysis.

In another embodiment, we provide active control structures for reducing various field artifacts or the like, such as fringing effects at the filter electrode edges. In another embodiment, we achieve ion focusing by field control, wherein a grid or array of electrodes is driven to selectively generate a non-uniform field to focus the ion flow in the flow path. This same grid may also be driven to gate ion flow, such as for time of flight analysis.

The invention may also provide other aspects, such as ion steering and ion flow compensation, including selective changes of ion flow from one flow path to one or another flow path. This effort may be all within one device or may assist coupling from one DMS system to another system (like a mass spectrometer).

In another embodiment, the flow path includes control surfaces in contact with a plurality (i.e., an array, grid, or set) of control electrodes. This "control array" may passively or actively affect ion behavior in the flow path. This control function may be performed along a flow path structure, layer, surface, covering, coating, substrate, region, or the like.

In several embodiments we use a control structure that is generally described herein as "partially conducting", which means having some capacity to conduct a charge but still performing an isolation or insulation function between electrodes. This control structure may also include use of a plurality of control elements whose combined effect is to be partially conducting, although individual elements may be fully conductive.

The overall effect of being "partially conducting" can be understood in the sense of being conductive enough to enable bleeding off or removing of charge as it is being built-up on flow path surfaces but controlled or insulating or insulated or isolated enough to avoid disrupting analytical operations.

In one illustration of a partially conducting material we include resources, such as semiconductor material, resistive paint, doped glass, use of ion implantation, or the like applied to a substrate. The resistance of the material overall may be governed by selected geometry and voltage, as well as material properties. In practice of several embodiments of the invention, the range of resistance is as wide as 10² ≤ohms/square >10¹⁴ and preferably within the range of 10⁷ ≤ohms/square ≥IO^{1 1}.

In one embodiment of the invention, a DMS device has a structure which defines a flow path. The flow path includes facing partially conducting layers of control material with a plurality of control electrodes forming facing control arrays. These control arrays are addressed and driven to control motion of ions in the flow path. Such control layers enable conveying, controlling, neutralizing, processing, and/or passing, selected ions and ion species. These arrays can provide the filter electrode function or can be isolated from the ion filter electrodes. These arrays may be used for charge dissipation as well as other ion flow control functions. It will be appreciated that both method and apparatus for controlling ion behavior in an ion-based analysis system are disclosed. Embodiments include an ion source, an ion flow path, an ion concentrator including electrodes facing each other in the flow path, an ion filter including electrodes separated by an analytical gap, and a system for controlling ion behavior between the electrodes and a control system. In one example, such control system generates at least one electric field whereby ions in the flow path are controlled, e.g., concentrated in the ion concentrator. The concentrated ions are separated according to ion-mobility-based behavior in the filter.

A result of achieving this level of field control in a DMS system is improved ion flow behavior, higher ion filtering efficiency, and improved detection capabilities.

The following description sets forth details of a DMS device in practice of the invention, a mass producible DMS chip assembly in practice of the invention, and further innovations in ion control in a DMS embodiment of the present invention. These descriptions are by way of illustration and not by way of limitation of the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIGS 1A and IB show mobility scans plotting detection intensity versus compensation voltage for a given field strength in a DMS, for acetone alone (1 A) and for a combination of o-xylene and acetone (IB).

FIG 2 is a schematic of a field asymmetric ion mobility spectrometer. FIG 3(A) is a side perspective view of an embodiment of the invention. FIG 3(B) is a perspective view of a substrate with electrodes in practice of an embodiment of the invention.

FIG 3(C) is a perspective view of a substrate with electrodes in practice of an embodiment of the invention. FIG 3(D) is a perspective view of spacer frame in practice of an embodiment of the invention.

FIG 3(E) is a side schematic view of a DMS chip in practice of an embodiment of the invention.

FIG 3(F) is a schematic of a disposable sensor with a socket. FIG 4(A) is a side perspective view of a pair of partially conducting control material layers in practice of an embodiment of the invention.

FIG 4(B-D) illustrate electrode configurations in practice of embodiment of the invention.

FIG 4(E) is a side view of a DMS system in practice of an embodiment of the invention.

FIG 5(A-C) shows alternative charge dissipation embodiments of the invention.

FIG 6(A, B) are schematic views of alternative embodiments of the invention having multiple flow paths. FIG 7(A-D) show alterative field effects in practice of an embodiment of the invention.

FIG 8(A) shows a side schematic view of an alternative DMS chip in practice of the invention.

FIG 8(B) shows an alternative detector arrangement in practice of the invention.

FIG 9(A,B) show the before and after effect on fringing fields in practice of an embodiment of the invention.

FIG 10 shows an embodiment of the invention including a varying flow path.

FIG 1 lA(l-5) show electrodes and drive signals in practices of the invention. FIG 1 lB(l-2) show fields developed in practices of the invention. DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows. While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. DMS

DMS is a relatively new technology which is capable of separation of ions in a fluid flow. Illustrative examples of mobility scans based on the output from a DMS device are shown in FIGS 1 A and IB. In FIG 1A a single compound, acetone, was submitted to the DMS analyzer. The illustrated plot is typical of the observed response of the DMS device, with detected acetone ions in this example forming a peak intensity at a compensation voltage of about -1.5 volts. This is useful information, such that future detections of a peak at this compensation in this device is indicative of detection of acetone .

In FIG IB, the analyzed sample consisted of acetone and an isomer of xylene (o-xylene). The acetone peak appears at about -2.5 volts while o-xylene appears at about -4 volts. Data representing these detection peaks can be compared against stored data for known compounds for this device and the applied RF field and compensation, and identification is made based upon a data match. FIG IB demonstrates unique detection peaks according to ion mobility characteristics for different ion species in the sample under test, i.e., o-xylene and acetone.

IMS and DMS systems offer low and low- high field characterizations of ion species, respectively. The present invention improves the performance of such ion- based analytical systems.

DMS ASSEMBLY

The present invention may be practiced in a variety of ion-behavior enhancing embodiments. An illustrative DMS assembly according to embodiments of the present invention is shown in FIG 2. Apparatus 10 has an inlet 12 that accommodates the flow of a carrier gas G carrying sample S into the device and then along flow path 11. The sample is drawn from the environment or received from a front end device, such as a gas chromatograph, and flows from inlet 12 to ionization region 14 along the flow path.

Compounds in the sample are ionized by an ionization source 16 as the sample flows through ionization region 14, creating a set of ionized molecules 17+, 17-, accompanied by some neutral molecules 17n of various chemical species. Ionized monomers and/or dimers, etc. are created during such ionization. Also clusters of ions may be created when a monomer combines with water molecules or other background molecules, in an ionized combination.

In practices of the invention, a DMS system receives a sample in a fluid ' flow, filters the ionized fluid flow and passes ion species of interest for down stream processing. In a preferred practice, the ions are carried by a gas stream (sometimes referred to as a carrier gas) through stages of the system (e.g., into filter 24 and toward detector 32), as taught in US Patent No. 6,495,823, incorporated herein by reference. Alternatively, the sample may be conveyed via an electric propulsion field, with or without carrier gas, as taught in US Patent No. 6,512,224, incorporated herein by reference.

In the embodiment of FIG 2, carrier gas G carries the ions into analytical gap 18 between filter electrodes 20, 22 of ion filter 24. A compensated asymmetric RF filter field F is developed between the ion filter electrodes in the analytical gap (e.g., 0.5mm) between the electrodes. The strength of the field varies according to the applied RF voltage (Vrf) in the gap. The RF field may be compensated, such as by application of a DC offset (Vc), which can be scanned. Compensation may also be implemented by varying other aspects of the filter field conditions on a species- specific basis.

In the embodiment of FIG 2, a detector 26 is on-board system 10 and takes the form of at least one electrode, and preferably includes a plurality of electrodes, such as opposed electrodes 28 and 30, associated with the flow path downstream of filter 24. However, alternatively, systems of the invention may include detecting the filter output with a mass spectrometer (MS) or other external detection system. In one embodiment, the invention improves species separation as a front end to enhance MS detection.

Control unit 40 preferably performs a number of important actions in accordance with the present invention, and may incorporate various devices or functions for this purpose. These may include RF voltage generator 42, an optional compensation voltage generator 44, a microprocessor unit (MPU) 46, memory 47, an analog-to-digital converter 48, and display 49.

Microprocessor 46 provides digital control signals to the RF voltage generator 42 and compensation voltage generator 44 to generate the desired compensated drive voltages for filter 24. These devices may also include digital-to- analog converters and the like, although not shown in detail. In the embodiment of FIG 2, control unit 40 biases and monitors the electrodes 28, 30 of detector 26. Microprocessor 46 correlates applied compensation and RF voltages with observed responses at detector 26, via analog-to-digital converters 48. Matching of this detection data against stored detection data in memory 47 enables making a species identification.

In practice of embodiments of the invention, applied peak RF voltages can range from less than 1,000 V/cm to 30,000 V/cm. The frequency may range from under 1 and beyond 20 Megahertz (MHz), depending upon species. In one embodiment a duty cycle of 30% is employed at higher frequencies for good effect, although other operating ranges, voltages, field strengths, duty cycles, wavelengths and frequencies are possible in embodiments of the present invention.

Apparatus of the invention are very stable and test results are repeatable. In a preferred practice of the invention, we use a library of information for identifying detected species, in view of compensation, RF and other field conditions. It is also within the scope of the invention to calibrate the system using the reactant ion peak (RIP) or a dopant peak, for example, among other techniques. - l i ¬

lt will be appreciated that ions are separated based on mobility differences in the filter field F in the analytical gap 18 according to the filter field conditions. Field F can be held at a fixed periodic value, wherein the system is dedicated to detection of a particular ion species at a single data point, or the field conditions can be varied for generation of a plurality of data points. As well, a particular field parameter can be scanned to generate a mobility scan, wherein field conditions are set to a particular value except for at least one mobility-affecting parameter that is swept through a range so as to generate a mobility spectrum for the sample under test. This is performed under direction and control of control unit 40.

MASS PRODUCIBLE DMS CHIP ASSEMBLY

A mass producible DMS chip 100, formed into an assembly 101, is shown in FIG 3(A-E) performing an I/O function, a processing function and a control function. The I/O function includes an inlet tube 102 for receipt of a gas sample from the environment (or from a GC output 103 or the like), and an outlet tube 104 which may be coupled to a pump 105 for exhaust of gas flow. (It will be appreciated that while inlet and outlet tubes are shown, alternative passages, pathways, orifices, openings, apertures, or other means of connection, ingress and egress, are within the scope of the invention.)

Chip 100 is preferably mounted into socket 106, which may be a conventional DIP or a custom socket, for off-board connection of the chip, such as for communication with off-board drive and control electronics 107, similar to the function of section 10C discussed above. Spectrometer system 101 functions similar to that of system 10 described above, wherein the flowing sample is ionized and is filtered in the filter section preferably according to the DMS techniques.

An illustrative chip 100 includes filter 108F and detector 108D (indicated by dotted outline on the face of chip 100 in FIG 3(A)). The system is controlled and ion detection signals are evaluated and reported by the controller section 107. Controller 107 may be on-board or off-board. Chip 100 has electrical connectors, such as leads 116, bonding pads 116c, or other connection arrangements, enabling connection to off-board systems, controls and the like.

In an illustrative embodiment of the invention, chip 100 includes substrate 110 (FIG 3(B)) and substrate 114 (FIG 3(C)). These substrates are separated by a spacer frame 112 (FIG 3(D)). Substrates 110 and 114 and spacer frame 112 are sealed together to form an enclosed flow path (with an enclosed channel 140) while forming a sealed housing 115. The inlet tube 102, outlet tube 104, ion source 109 and electrical leads 1 16 are mounted on the housing. In one embodiment, the inlet tube is provided with an optional heater 102h, for heating the sample input.

Ionization of chemical sample in practice of the invention may be achieved by various techniques. Ionization source 109 may be an ultraviolet photo-ionization lamp, a plasma or radioactive source, ESI arrangement, laser ionization, or the like, and provides a mixture of ions corresponding to chemicals in the gas sample. The ionized sample is then passed to ion filter 108F where the applied compensated RF field between the filter electrodes selects and enables a particular ion species to pass through the filter. Once through the filter, the ion species is detected in detector 108D. If the filter field is scanned, then a detection spectrum can be generated for the sample.

In FIG 3(E), an ionization source 109 is integrated into chip 100 to ionize the sample in the gas flow from inlet 102, which is drawn through the DMS filter 108F by pump 105, under direction of drive and control electronics 107, similar to the function described above for chemical sensor system 10.

In the embodiment of FIG 3(A), inlet tube 102 and outlet tube 104 are mounted to the back surface 110b of substrate 1 10. As shown in FIGS 3(B-E), the inner surface 110a of substrate 110 and inner surface 114a of substrate 114 include metallization patterns which define an illustrative DMS system. As shown in FIGS 3(A-E), an illustrative system of the invention includes substrate 110 includes first metallization portion 118m that defines attraction electrode 118 and its extension that forms bonding pad 118c to which a lead 118/ is attached. Substrate 110 further includes second metallization portion 120m that defines filter electrode 120 and its extension that forms bonding pad 120c to which a lead 120/ is attached. Substrate 110 also includes third metallization portion 122m that defines detector electrode 122 and its extension that forms bonding pad 122c to which a lead 122/ is attached.

First substrate 110 includes fourth metallization portion 124m that defines shielding electrode 124 and its extension that forms bonding pad 124c (to which a lead 124/ will be attached). Shielding electrode 124 further defines shield 124a which shields detector electrode 122 from the RF filter signals, thus reducing leakage between the ion filter 108F and detector electrode 122 of detector 108D and thus reducing noise in the ion detection signal.

An ionization access port 126 (a via or through hole) is defined in either or both substrates to enable ionization sources 109 to interact with the sample. Source 109 is shown mounted on the back side 114b of substrate 114 in FIG 3(E). As shown in FIG 3(C), the front side 114a of substrate 1 14 includes first metallization portion 128m, through which port 126 extends, and defines a guiding electrode 128 and its extension that forms bonding pad 128c to which a lead (not shown) is attached.

Substrate 1 14 further includes second metallization portion 130m that defines filter electrode 130 and its extension that forms bonding pad 130c to which a lead can be attached. Substrate 114 also includes third metallization portion 132m that defines detector electrode 132 and its extension that forms bonding pad 132c to which a lead can be attached.

Substrate 114 also includes fourth metallization portion 134m that defines shielding electrode 134 and its extension that forms bonding pad 134c to which a lead can be attached. Segment 134m further defines shields 134a, 134b, 134d which shield detector electrode 132 from the filter signals, thus reducing leakage current between filter 108F and detector electrode 132 and thus reducing noise in the ion detection signal. Spacer (or spacer frame) 1 12 is preferably a strip of insulating material

(which itself may be semi-conductive or otherwise static or charge dissipative) with a central through-slot 139 that cooperates with the substrates 110, 114 to define the drift channel 140. The sides of drift channel 140 are contained within the spacer frame 112 extensions 112a and 1 12b. Substrate 110 is placed on one side of spacer 112 such as bonding agent 142 (e.g., glass frit or epoxy) in between, and substrate 114 is placed on the other side of spacer 112 with bonding agent 142 in between. The workpiece is processed to set the bonding agent and form a sealed structure 100. A formed and sealed chip structure 100 using bonding agent 142 is shown in FIG 3(A) in the magnified view at "A". However, it will be appreciated that bonding agent is only one of several possible sealing approaches, such as anodic bonding, and possibly also including mechanical fasteners such as crimps and screws, and the like.

Preferably this structure forms the basic chip assembly 100 and defines an enclosed and sealed flow path 144 with access to the flow path for fluid flow. The flow path is accessed at one end 140a of channel 140 by, and is in communication with, inlet tube 102 mounted over port (or through hole) 148 in substrate 110. The flow path 144 is vented at the other end 140b by, and is in communication with, outlet tube 104 mounted over port (or through hole) 150 in substrate 110.

In operation, carrier gas 102s, which may include a chemical sample to be detected, is introduced into flow path 144 via inlet tube 102, and then passes into ionization region 146 and is subjected to the ionization source 109. In one embodiment, source 109 emits ions that pass tlirough port 126, guided by a bias applied to guiding electrode 128 (e.g., a positive bias for a positive ion) and attracted by attraction electrode 118 into the flowing sample 102s. The attraction electrode is driven by an attraction bias (e.g., a negative bias for a positive ions). The ions ionize compounds in sample 102s creating ions ("+","-") that are carried in the flow between electrodes 120, 130 of filter 108F, where the ions are subjected to the compensated high field asymmetric waveform ion mobility techniques (as described earlier), and filtered (selected) ions pass through the filter. Ions are detected at electrodes 122, 132 of detector 108D. The carrier gas flow then vents from the flow path 144 at outlet 104.

As will be appreciated by a person skilled in the art, flow path 144 may be at, above or below ambient pressure. In some applications, the carrier gas and sample flow is generated by a higher pressure at the inlet, such as produced when eluting samples from a GC, and the sample is carried along the flow path thereby. In another application, the flow is generated by a pressure gradient at the detector, such as at the inlet of an MS and the gas is drawn thereby. The gas flow may also be generated by a pump 105 at outlet 104, FIG 3(A). This enables operation at different pressures as selected for specific species identifications.

It is further noted that while a particular pinout is shown in FIG 3(A) for mounting chip 100 in socket 106, alternative configurations are possible, all within the scope of the invention. For example, as shown in FIG 3(F), a chip assembly 300 is mounted into a socket 306 according to the invention, when an inlet 302 mounted on the socket provides in-flow to chip 300 via ports 302a, 302b and exhaust at outlet 304 via ports 304b, 304a. In this embodiment, sealing elements 308 and 310, such as o-rings, are part of the socket assembly and assure leak-free coupling of the chip 300 to the socket 306 between cooperating ports 302a/302b and 304a/304b.

ION CONTROL:

The present application features both passive and active ion control. In one embodiment charge dissipative surfaces in the flow path prevent charge buildup that otherwise can impact ion behavior. In another embodiment of the present invention, we implement electronic control of ion behavior for optimization of mobility-based ion species filtering and control. In an illustrative practice of the invention we form a structure of partially conducting control material supporting a plurality of control electrodes. These supported control electrodes are laid out as an addressable array (which may be a grid of electrodes). Controlled voltages are applied to such addressable array of electrodes to affect and control local ion behavior in the flow path.

It will be appreciated that a control function of the invention may be achieved using a material element or elements (in the flow path) having the capacity to conduct a charge while simultaneously maintaining sufficient electric separation between electrodes in conductive contact with that material. Such control material is generally described herein as "partially conducting", which may also have the connotation of being somewhat "resistive", or as having such control result. Thus several fully conductive elements may be gathered in an area to perform a control or a charge dissipating function.

In illustrative embodiments, the partially conducting control material may be a structure, layer, surface, covering, coating, substrate, region, or the like. In one embodiment, the control material is associated with control of an addressable array of electrodes. In one illustration, resistive paint (used in electronic circuit applications) is applied to a non-conducting substrate with an array of electrodes formed thereon. In another illustration of such control material, a sheet of semiconducting material is used as a partially conducting member and as a support member (e.g., a substrate) for the array of electrodes that are used for such control function. Yet other illustrations will occur to those skilled in the art.

In one embodiment of the invention, shown in FIGS 4(A-E), we implement electronic control of ion behavior via partially conducting control material forming surfaces in a DMS chip embodiment 200. In particular, we define flow path 201 between structures 210, 214 of chip 200. These structures 210, 214 are formed using, with or as partially conducting control material layer 211, 215, respectively. The charge dissipating feature of the invention may be practiced as set forth in FIG 5(A-C).

FIG 5(A-C) shows several illustrative embodiments of charge dissipating features of the invention on substrates 110 (with spacer 112 and other substrate 1 14 not being shown). Filter electrode 120 and shielding electrode 124 are shown on substrate 1 10 separated by a layer 222 provides charge dissipation according to the invention in the partial view of FIG 5(A). In FIG 5(B), a charge dissipating electrode (or collection or array of electrodes) 223 performs the charge dissipating function of the invention between electrodes 120 and 124. In these embodiments, charge buildup is minimized as will provide improved ion analysis. In FIG 5(C), a charge dissipating void 224 is formed in substrate 225, wherein charge buildup is effectively removed from the flow path between electrodes 120 and 124 and avoids the unwanted charge buildup. Optionally a charge dissipating layer 222 can be formed at the bottom and/or sides of the void 224 to further assure removal of charge buildup thereat.

In a further application of the invention, each of the partially conducting control material layers 211, 215 includes an array of electrodes 211 A, 215A, respectively, as shown in FIG 4(A-E). The arrangement of electrodes for a particular array may be chosen for particular purposes. Illustrative array patterns are shown in FIGS 4(A-D).

In one embodiment these electrodes are used for charge dissipation, in another embodiment they are used for ion flow control which may include formation of the DMS filter field. In another embodiment they are used for both functions. In one embodiment, these arrays face each other and enable forming the DMS filter field F across the flow path. This arrangement enables forming a non-uniform filter field which enables ion focusing to concentrate desired ion flow. In one practice of the invention at least one array is employed which faces at least one electrode but preferably faces an opposed array of electrodes on opposed sides of flow path 201 but that are driven to create a non-uniform field to achieve a focusing effect.

In the embodiment of FIG 4(A), arrays 211 A, 215 A, are formed on a partially conducting control material layer 211, 215, respectively. These arrays include a plurality of electrodes, such as electrodes 21 la-n of array 211 A and electrodes 215a-n of array 215 A.

In one embodiment, the rear side of each such array provides access to such electrodes for attachment of leads. The rear side of partially conducting control material layer 211 is shown in FIG 4(A) with electrodes 21 la-n forming the array 211 A and having attached leads 21 la/-n/. A like configuration may be applied to layer 215 with electrodes 215a-n of array 215A and leads 215a/-n/. As shown in FIG 4(E), structures 210, 214 act as support members and cooperate with spacing sidewalls 216, 218, to form a housing or package 220 for DMS chip 200. These sidewalls may be formed in various manners. For example sidewalls 216, 218 may be discrete such as a spacer frame like frame 1 12 or may be formed as extensions of the structures 210, 214, as shown in FIG 4(E). These sidewalls may be used as confining electrodes or charge dissipation, and will include conducting or partially conducting surfaces.

In one embodiment, the I/O function includes an inlet tube 202 for receipt of a gas sample from the environment (or from a GC outlet or the like), and an outlet tube 204 which may be coupled to a pump (not shown) for exhaust of air flow and/or delivery of ions downstream. An ionization source 219 may also be provided which may include UV, Ni63, ESI, corona discharge, atmospheric pressure chemical ionization (APCI), matrix assisted laser desorption ionization (MALDI), or the like.

Ion filter 213 performs functions such as filter 108F in the configuration of chip 100, which preferably also includes a detector 221 such as detector 108D in the configuration of chip 100. Electrode control is provided by a controller, such as electronics controller 107 associated with chip 100. The system is controlled and ion detection signals are evaluated and reported by the controller. Chip 200 has electrical connectors, such as leads 21 la/-n/ and 215a/-n/, enabling connection to the controller whether it is situated on or off-board.

In operation, sample S is drawn in through inlet 202 and flows along flow path 201, first being subjected to ionization source 219. Ions and molecules 17+, 17- ,17n now flow from the ionization source in the vicinity of inlet 202 toward outlet 204 through filter 213 and filter field F. Electrodes 21 la-n, and 215a-n, of the respective control arrays 211 A, 215 A are addressed, and controlled DMS voltages are applied to such members, to create a compensated RF field to affect ion behavior accordingly. Ions passing through filter field F may be detected at detector 221, such as in the manner discussed above with respect to chip embodiments 10 and 100. It will be further appreciated that the array of electrodes is formed on an insulating surface or directly on the charge dissipating surface in practice of the invention. CONTROL OF ION MOTION:

In practice of the invention, controlled voltages are applied to the control surfaces or control electrodes (which may be formed as arrays) to affect and control local ion behavior, density, or concentration and preferably to affect ion velocity and direction of travel by species. As an illustration, in a device 200 with arrays 211 A, 215A facing each other over the flow path 201 and ions flowing through the analytical gap G in between these arrays, several aspects of species-specific ion motion control may be implemented. This ion motion control may include application of a longitudinal propulsion field for propulsion of ions along the flow path, generation of the DMS RF filter field to affect differential transverse ion motion in the filter, and compensation of the DMS filter field to select ion species for passing through the filter field. The electrode arrays may also be driven to steer, focus, confine or trap the ion flow, as well as to reduce fringing fields or to achieve other field effects.

Longitudinal propulsion of ions along a DMS flow path has been set forth in copending US Patent Application Serial Number 10/082,803, filed 02/21/02, Attorney Docket M002CP, incorporated herein by reference. Therefore it will be understood by a person skilled in the art that electrodes in the arrays of electrodes 21 1 A, 215 A can be driven to achieve such ion propulsion.

Generation of the DMS RF filter field and compensation of the field have been set forth in copending US Patent Application Serial Number 10/321822, filed 12/16/02, Attorney Docket M001CN, incorporated herein by reference. Therefore it will be understood by a person skilled in the art that electrodes in the arrays of electrodes 211 A, 215A can be driven so as to create field F across the flow path that is compensated to pass ion species of interest through the filter (and/or to scan a sample in the filter). Other forms of compensation may be achieved in practice of the invention; such other compensation may be achieved by adjusting a number of filter field factors and as taught in copending US Provisional Patent Application Serial Number 60/468306, filed 05/06/03, Attorney Docket M085, incorporated herein by reference, and US Patent Application Serial Number 10/462206, filed 06/13/03, Attorney Docket Ml 06, incorporated herein by reference.

It will be appreciated that ion steering can be accomplished by driving of electrodes or combinations of electrodes of the electrode arrays 211 A, 215A. In one illustration, as shown in FIG 6(A-B) a surface 226 of a DMS filter 228 has electrode array 230A formed on partially conductive material layer 232, performing ion control functions in cooperation with partly shown array 236A on opposed DMS filter surface 234 on partially conductive material layer 238. Alternatively, layer 232 can be a resistive coating over which a voltage is dropped to create a steering field to steering ions accordingly.

In this illustrative embodiment, this filter assembly 228 is located at the output of a filter 213 (like filter 213 of FIG 4(E)). The ion species output from filter 213 can pass across and through flow path 240 of filter 228 across guard electrode 251 to reach detector 252 for detection and identification. However, a steering electrode 254 at one end of flow path 240 can have a potential applied to steer and propel ions of that polarity (e.g., positive) along flow path 240 so as to be subjected to arrays 230A, 236A of filter 228.

Arrays 230A, 236A enable performance of a number of local functions that impact the local ion flow. As well, an additional filter 260 may be added to flow path 240 to enable further sample/species manipulation. If the partially conductive material layers do not extend to the end of this assembly, then a further partially conductive layer 262 can be applied to couple filter 260 and guard electrode 264 to reduce charge buildup. Detector 266 detects the filtered ions. The guard electrodes are isolated such as by insulated land 265 from the detector electrodes 266 so as to prevent filter signals from interfering with the detection signal. In a further embodiment of the invention, ions that are steered by electrode 254 may have an angular vector that can be anticipated and accommodated by having an angled filter path. Thus in FIG 6(B), steering of ions takes the resulting path imposed by action of electrode 254 upon the flowing ions. Now these ions are captured and carried along flow path 270. An additional collection or attraction electrode 271 may also be provided to further assist ion separation or analysis.

Discussion of ion steering calls attention to a further aspect of the invention, wherein control, configuration and steering of the ion flow can be exploited and managed. Turning to FIG 7(A), we show a filter 272 having upper and lower electrode arrays 274 A, 276A formed on partially conductive material layer s 274, 276, respectively. As will be appreciated by a person skilled in the art, by appropriately driving various ones of these electrodes, ions of a given polarity can be steered or collected at various locations within the flow path. An illustration follows.

Ion control is further explored with respect to FIG 7(B), wherein the effect of having different potentials (varied over time) applied to parallel electrode columns 280, 282, 284 is to create a potential "well" or "trough" 286 in which ions of a given mobility aspect will collect. This produces a focusing effect. This can be explained with respect to polarity, for example, wherein electrodes 280, 284 are positive and electrode 282 is less positive, positive ions, ions +,+,+,+ in FIG 7(B), will collect in the trough. Now diffusion losses can be reduced and a more intense filter signal can be outputted.

As shown in FIG 7(C), a non-uniform field can be generated by driving a different number of the facing electrodes in opposed electrode arrays 274 A, 276A. For example, electrode E₅ of the plurality of electrodes Eι-E_n is driven in array 274 A and cooperates with a plurality of driven electrodes Eι-E_n in array 276 A. It will be appreciated that the field F generated between these electrodes is concentrated at the single electrode E₅ of array 274A while it is distributed between electrodes El-E„ (and therefore is at lower field strength) along the face of array 276A. This creates an ion focusing effect that mimics the effect of inner and outer curved electrodes as in a coaxial cylindrical FAIMS device. The result of the non-uniform field is to have the desired focusing effect on demand for collecting or concentrating of ions for the ion analysis and detection. This on-demand or switchable or controllable ion control feature is useful, since a particular effect (such as ion focusing) has a different impact on different ion species and may not be desired at all times. It will be further appreciated that facing electrodes of different size will generate a non-uniform field, which can be practiced in an embodiment of the invention.

It will be appreciated that the foregoing ion control, ion confinement, ion focusing, ion trapping, and ion steering can be adapted to a process of texturing, controlling, and manipulating ion flow in the filter field for achieving desired ion species behavior effects.

CHARGE DISSIPATION

DMS systems work favorably, and can benefit from control of charged surfaces along the flow path. In one embodiment a charge field is established along the flow path. In anther embodiment, filter and detector electrodes are isolated from each other to prevent interfering with ion detection. In one embodiment of the invention, this can be implemented by insulating the electrodes, such as by building on the insulated surfaces of substrates.

At time it may be required to reduce charge buildup on the flow path surfaces (e.g., the surface 113 of substrate 1 10, FIG 3(B)). The present invention provides the option of charge dissipation without interfering with action of the filter and detector electrodes. Generally speaking, in one embodiment, a discharge path is provided from the flow path to the system ground. As shown in FIG 4, partially conductive layers 211, 215 provide such charge-dissipative surfaces.

In one example, we practice electrospray ionization in DMS while reducing the effect of surface charge buildup on the exposed surfaces of the flow path, which includes exposed surfaces in between the electrodes. The charge-dissipative (e.g., partially conducting) control material of the invention forms a charge dissipation path to reduce charge buildup and the ionized electrospray flows through the DMS filter with regularity.

Thus the control material of the invention is used to form a charge- dissipative surface to replace or augment or cover or cooperate with the filter electrodes and the other surfaces of the flow path.

The embodiment of FIG 3(E) can be modified according to the invention, shown in FIG 8(A), to utilize an electrospray head 109ES attached to substrate 114 as ionization source 109. In an ESI-filter assembly 300, carrier gas 102g is introduced via inlet 102 and the sample to be filtered is ionized and introduced via the electrospray head 109ES as ionized sample stream 109s. The electrospray tip 109t is held at a high electrical potential (Vtip) and charges the atomized ionized spray molecules (positive or negative but shown as +,+,+) which are attracted by oppositely charged attractor electrode 118 as they flow through ionization access port 126 into flow path 144. The ionized sample 109s is conveyed along the flow path and into the ion filter 108F defined in the analytical gap between filter electrodes 120, 130.

In this illustration, these ions (+,+,+) are subjected to the compensated asymmetric RF field of filter 108F. The species of ions that are returned toward the center of the flow by the applied compensation will pass as species +ι into the detector. If these are positively charged ions, then a positive bias on detector electrode 132 steers the ions toward negatively biased detector electrode 122 with which these positive ions make contact and where they deposit their charges. (It will be appreciated that negatively charged ions can be detected in a similar manner, with opposite polarity biasing.)

The ion species detection and the intensity of detection are correlated with the parameters of the filter environment, which is evaluated against a library of information for identifying detected species. Finally, the ions +ι having lost their charges return to being neutral molecules and they and the rest of the gas flow are carried out of the detector region via outlet 104.

FIG 8(B) shows an alternative arrangement, where the separated ions +ι, +ι, +ι are outputted for external use. In one embodiment, detector electrode 122 is opposite an orifice 160 in substrate 114 and the biased electrode 122 (e.g., positively biased) steers ions +ι, +ι, +ι toward the orifice where they flow out of the flow channel. In one embodiment, this enables the ions to be delivered to the input of a mass spectrometer 162, which may be assisted by an attraction electrode 164 (in this example negatively biased to attract ions +ι, +ι, +ι ). This arrangement may further include an electrode ring 166 which cooperates with orifice 160 for the passage of ions +ι, +ι, +ι out of the flow channel, while also being capable of being biased to attract a portion of the ion flow +ι, +ι, +ι. Now feedback and control data may be obtained at electrode ring 166 as a detector, for the operation of the filter system of the invention, while also enabling a desired ion output.

It will be understood that an electrospray head provides a highly ionized sample flow into the flow path. In an illustration of the invention, we add the partially conductive aspects of the invention. Thus, as shown in FIG 4, partially conductive layers 21 1, 215 are provided. These charge-dissipative surfaces carry away the "static" charge build-up while performing ion analysis in the electrospray- DMS system.

REDUCTION OF FRINGING FIELDS

The present invention may also be applied to reducing the fringing field at the edges of the filter electrodes. In one aspect, the charge dissipation quality of the partially conducting control material layers of the invention reduces fringing fields. In another aspect, we can reduce the impact of fringing effects at the edges of the filter electrodes by appropriately driving electrodes of arrays 211 A, 215 A to anticipate the fringing effects and adjust ion behavior. It will be appreciated that the DMS filter field generated between the faces of the filter electrodes, such as filter electrodes 20, 22 of FIG 2 or electrodes 120, 130 of FIG 3(F), are normally straight, uniform and well-defined. This same result can be achieved between the faces of electrodes arrays 211 A, 215 A of FIG 4(E).

However, the fringing field around the electrode edges can be irregular and can negatively impact ion flow. As shown in FIG 9(A), the fringing field FF1 at the edges of the filter field F have non-linear shape as will impact the local ion flow. Nevertheless, formation of the filter arrays 211A, 215A on the partially conducting control material layers 211, 215 enable operation for dissipating local field disruptions. Therefore, as shown in FIG 9(B), in an embodiment of the invention using the partially conducting control material layers, the fringing field FF2 has been substantially straightened. While there still remains a vector associated with the fringing field, it is more uniform and will have more predictable impact on local ion behavior. Furthermore, it will be appreciated that this remaining vector can be neutralized by selectively driving selected electrodes of the array of electrodes.

In the embodiment of FIG 10, a non-flat flow path is shown having electrodes 420, 430 of ion filter 410. The electrodes are formed on substrates 402, 404. Also provided are charge dissipating surfaces 406 in practice of the invention.

In a further embodiment of the invention concentrator electrodes are driven sequentially. This phased drive is shown in FIG. 1 lA(l-3), where impulses E_A, E_B, Ec, E_D are sequentially applied to respective electrodes a, b, c, d, FIG 1 1 A(2). Note that this is an asymmetric waveform 402. As will be understood by a person skilled in the art, and as shown in FIG 1 lB(l-2), the effect of this rolling field is to energize the ions toward the center of the flow path. In this manner, substantial ion flow control can be imposed in practice of embodiments of the invention. It will therefore be appreciated that ions can be concentrated such as between the arrays of electrodes of the invention, and then can be filtered as disclosed. The concentrated ions flow downstream for filtering and detection with improved resolution and better sensitivity. The present invention enables analysis of compounds by high field asymmetric waveform ion mobility techniques in a compact package that can be manufactured using high volume techniques that result in low per chip costs and yet produces results comparable to expensive analytical equipment. The present low parts-count chip design further reduces assembly costs and more importantly lessens the opportunity for variability from chip to chip and system to system, thus improving product reliability. Chips and systems according to the invention are light-weight and yet provide the ability to apply highly effective analytical equipment in the field and in industry beyond the laboratory environment.

The present invention applies to various ion mobility devices, including

DMS and IMS and further including planar, cylindrical, radial and other device configurations. Furthermore, various modifications of the specific embodiments set forth above are within the spirit and scope of the present invention. Other shapes or configurations of structures, such as electrodes, spacers, and substrates, are within the spirit and scope of the present invention. The specific construction techniques set forth above are not a limitation of the present invention.

The terms detector, spectrometer and sensor may be used interchangeably for purposes of this disclosure within the spirit and scope of the present invention. The terms drift tube, flow path and flow path may be used interchangeably and remain within the spirit and scope of the invention. The terms contact pad and bonding pad likewise may be used interchangeably within the spirit of the invention. The terms upper lower inner and outer are relative, are used by way of illustration and not by way of limitation. The terms tubes, conduits, passages ways and the like may be used interchangeably within the spirit of the invention. Furthermore, the examples and embodiments disclosed herein are shown by way of illustration and not by way of limitation. It will be further appreciated that the present invention is operable with gas and liquid samples, even though for convenience the illustrative examples above refer to samples in a gas flow. The scope of these and other embodiments is limited only as set forth in the following claims. While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

CLAIMS What is claimed is:

1. System for controlling ion behavior in an ion-based analysis device, said system comprising:

a flow path for the flow of ions, an ion source coupled to said flow path, an ion filter including electrodes separated by an analytical gap for generating an ion filter field in said flow path for filtering said flow of ions, and

a control structure for controlling ion behavior in said flow path, wherein ions are separated according to species based on ion-mobility-based behavior in said filter field.

2. System of claim 1 wherein said control structure is for generating an influencing field that influences said flow of ions in said device.

3. System of claim 1 wherein said control structure governs ion flow in said flow path to control local effects that impact ion behavior in the analytical field.

4. System of claim 1 wherein said control structure includes an influencing source that influences the analytical environment within said analyzer.

5 System of claim 4 wherein said control structure governs ion flow activity for any of the group of activities consisting of: focusing, trapping, confining, translating, steering, selecting, filtering, detecting and redirecting of ions in said flow path.

6. System of claim 4 wherein said control structure further comprises a plurality of control electrodes forming facing control arrays, said control arrays being addressable to control motion of ions in said flow path.

7. System of claim 1 wherein said system is a DMS system and is operated as a device selected from the group consisting of: spectrometer, filter, detector, and separator based on ion behavior in said filter field, wherein said filter field is a compensated asymmetric high-low varying RF filter field.

8. System of claim 1 wherein said system is operated to determine the time of flight of ions passing along said flow path.

9. System of claim 1 wherein said control structure includes a charge- dissipating control material in said flow path, wherein said control material is coupled to said system to prevent charge buildup in said flow path.

10. System of claim 1 further including an active control structure for reducing field artifacts in said flow path.

11. System of claim 10 wherein said artifacts include fringing effects at the edges of the filter electrodes.

12. System of claim 11 wherein said control structure includes a grid array of electrodes, wherein said array is driven to selectively control ion flow in said flow path.

13. System of claim 12 wherein said array is driven to provide a non- uniform field in said flow path.

14. System of claim 13 wherein said non-uniform field is ion-focusing in said flow path.

15. System of claim 14 wherein said filter electrodes are formed on substrates and said are spaced apart by a spacer to set said analytical gap and forming an enclosed flow path.

16. System of claim 15 wherein said control structure is formed on said substrates.

17. System of claim 1 wherein said control structure includes a control array of electrodes for affecting ion behavior in said flow path.

18 System of claim 1 wherein said control structure is at least partially conducting, having at least some capacity to conduct a charge without interfering with said filter electrodes.

19. System of claim 18 wherein said control structure includes a plurality of separated conductive electrodes whose combined effect is to be partially conducting relative to said filter electrodes, wherein said plurality is isolated from said filter electrodes for dissipating charge build-up in said flow path.

20. System of claim 1 wherein said control structure includes partially conducting material selected from the group consisting of: semiconductor material and resistive paint.

21. System of claim 20 wherein resistance of said material is in the range of 10² ≤ohms/square ≥iO¹⁴ . n

22. System of claim 21 wherein said range is within 10 ≤ohms/square

1 1

≥iO

23. Method for controlling ion behavior in an ion-based analysis system, said method including the steps of:

providing: a flow path for the flow of ions, an ion source coupled to said flow path, an ion filter including electrodes separated by an analytical gap for generating an ion filter field in said flow path for filtering said flow of ions,

providing a control structure for controlling ion behavior in said flow path, and

separating ions in said flow of ions according to species-based on ion- mobility-based behavior in said filter field.

24. Method of claim 23 further including the step of generating an influencing field that influences said flow of ions in said system.

25. Method of claim 24 wherein said influencing includes action from the group consisting of focusing, trapping, confining, translating, selecting, and filtering ions in said flow path.

26. Method of claim 25 wherein said device is system is a DMS system and is operated as a device selected from the group consisting of: spectrometer, filter, detector, and separator based on ion behavior in said filter field, wherein said filter field is a compensated asymmetric high-low varying RF filter field.

27. Method of claim 26 wherein said system is operated to determine the time of flight of ions passing along said flow path.

28. Method of claim 23 further comprising the step of providing said control structure with a charge-dissipating control material in said flow path, wherein said control material is coupled to said system to prevent charge buildup in said flow path.

29. Method of claim 23 further the step of actively controlling said control structure for reducing field artifacts in said flow path.

30. Method of claim 29 wherein said control structure includes an array of electrodes.

31. Method of claim 30 further including the step of isolating said array from said filter electrodes.

32. Method of claim 31 wherein said array is partially conducting and is coupled to said system for dissipating charge build-up in said flow path.