Device for performing field asymmetric waveform ion mobility spectrometry

Abstract

A FAIMS device comprises: a first segmented planar electrode, whose segments are in a first plane and extend in a direction parallel to an analysis axis; a second segmented planar electrode, whose segments are in a second plane and extend in a direction parallel to the analysis axis, wherein the first and second segmented planar electrodes are separated from each other to provide an analysis gap; a propulsion component for propel ions through the analysis gap; and a power supply; wherein the device operates in the following modes: a FAIMS mode, in which the power supply applies a first set of voltage waveforms to the segments of the first and second segmented planar electrodes to generate an asymmetric time-correlated electric field in the analysis gap for FAIMS analysis of the ions; and a transparent mode, in which the power supply applies a second set of voltage waveforms to the segments of the first and second segmented planar electrodes to focus the ions toward the longitudinal axis.

Description

Technical Field

[0001] The present invention relates to an apparatus for performing Field Asymmetric Waveform Ion Mobility Spectroscopy or "FAIMS". Background Art

[0002] Ion mobility spectrometry ("IMS") is an analytical technique used to separate ions in the gas phase based on their mobility in a carrier buffer gas.

[0003] In linear IMS, ions are separated according to their absolute mobility K.

[0004] In nonlinear IMS, ions are separated based on their response to a varying electric field.

[0005] Field asymmetric waveform ion mobility spectrometry ("FAIMS") (see reference [3]), also known as differential mobility spectrometry ("DMS") (see reference [4]), is a well-established nonlinear IMS method that separates ions by differences in mobility in a gas as a function of electric field strength as they pass through an analytical gap (also known as a "FAIMS gap"). These differences depend on the geometric structure and physical and chemical properties of the ions and gas molecules, but are only weakly correlated with the ion mass. The resulting strong orthogonality with a mass spectrometer (MS) makes FAIMS / MS systems (where ions are separated by FAIMS and then MS is obtained) a powerful analytical method. Multiple FAIMS / MS systems have been commercialized. However, customer acceptance has been limited to date, largely because satisfactory MS performance without FAIMS separation cannot be achieved except by physically removing the FAIMS device from the FAIMS / MS system (i.e., satisfactory MS performance cannot be achieved when the FAIMS device of the FAIMS / MS is operating in a "transparent mode" with the FAIMS separation turned off).

[0006] All FAIMS stages currently commercialized by major vendors (stand-alone or connected to a MS) operate at ambient pressure and employ a double sinusoidal waveform (superposition of two harmonics) or a close distribution with fixed frequency and HF / LF ratio. This distribution deviates significantly from an ideal rectangular waveform, which would theoretically maximize resolution.

[0007] Reference [1] describes the use of a vacuum differential ion migration device (DMS) in combination with a mass spectrometer. In particular, reference [1] describes the use of various DMS structures including multipole formats and planar formats. Reference [1] also teaches that the multipole format can provide two operating modes, one providing FAIMS separation of ions (separation mode) and the other allowing ions to pass through without FAIMS separation (transparent mode). Operating pressures and methods for providing a FAIMS power supply unit (PSU) are also disclosed. In reference [1], a transparent mode is achieved by using a coaxial multipole as a quadrupole, where the waveform is set to a duty cycle of 50% allowing transmission of all ions.

[0008] Reference [2] describes segmented electrodes for differential ion transport devices. In the present invention it is mentioned that a voltage can be applied to form a field "identical to the field formed between two concentric cylindrical electrodes" and "having a variable radius of curvature" (see column 4, lines 59-67). Thus, reference [2] indicates that a planar FAIMS can be used to generate the same field that can be generated between two concentric cylindrical electrodes, although there is no teaching as to why this should be done.

[0009] The present invention is designed based on the above considerations. Summary of the invention

[0010] A first aspect of the present invention provides:

[0011] An apparatus for performing field asymmetric waveform ion mobility spectrometry (FAIMS), the apparatus comprising:

[0012] a first segmented planar electrode comprising three or more segments, wherein the segments of the first segmented planar electrode are arranged in a first plane and extend in a direction parallel to an analysis axis of the device;

[0013] a second segmented planar electrode comprising three or more segments, wherein the segments of the second segmented planar electrode are arranged in a second plane and extend in a direction parallel to an analysis axis of the device, wherein the first segmented planar electrode and the second segmented planar electrode are separated from each other to provide an analysis gap therebetween;

[0014] a propulsion member for propulsing ions through the analysis gap in a direction parallel to an analysis axis of the device; and

[0015] power supply;

[0016] The device is configured to operate in the following modes:

[0017] a FAIMS mode, wherein the power supply applies a first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component;

[0018] A transparent mode wherein the power supply applies a second set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate a confining electric field in the analysis gap for focusing ions toward the longitudinal axis.

[0019] The present inventors have found that a pair of segmented planar electrodes is particularly suitable for providing good LP-FAIMS separation in efficient transparent mode.

[0020] Note here that neither reference [1] nor reference [2] discloses segmented planar electrodes being used in transparent mode.

[0021] According to principles known in the art, the asymmetric time-dependent electric field generated in the analysis gap (when the device is operated in FAIMS mode) can repeatedly oscillate (change back and forth) between a high field ("HF") state and a low field ("LF") state, wherein the asymmetric time-dependent electric field repeats at a predetermined frequency f every time period T. For a first portion of the time period T of the asymmetric time-dependent electric field, a set of high field ("HF") voltages can be applied to the segment to produce the HF state. For a second portion of the time period T of the asymmetric time-dependent electric field, a set of low field ("LF") voltages can be applied to the segment to produce the LF state. Therefore, for each segment, the (corresponding) first voltage waveform applied to the segment in FAIMS mode may include a HF voltage configured to produce the HF state and a LF voltage configured to produce the LF state. For each segment, the HF voltage and the LF voltage applied to the segment may be different in amplitude and polarity. In particular, the amplitude of the HF voltage may be larger than the amplitude of the LF voltage, but applied for a shorter amount of time. However, the shape of the asymmetric time-dependent electric field generated in the analysis gap (ie, the electric field contours) should be the same in both the HF state and the LF state.

[0022] The fraction of the time spent generating the HF field (by applying the HF voltage to the segments) within a time period T of the asymmetric time-dependent electric field is called the duty cycle d. The ratio of the time spent generating the LF field (by applying the LF voltage to the segments) to the time spent generating the HF field (by applying the HF voltage to the segments) within a time period T of the asymmetric time-dependent electric field is called the f-value, where f-value = (1-d) / d (e.g., d = 0.2 would give an f-value of 4).

[0023] As is known in the art, for a FAIMS device employing non-segmented planar electrodes, a "dispersion voltage" ("DV") can be defined, which is the maximum amplitude voltage applied to the planar electrodes of the device to obtain the HF state.

[0024] In the case of a FAIMS device employing a segmented planar electrode, the dispersion voltage may be defined as the maximum amplitude voltage applied to a segment (usually the central segment) of the segmented planar electrode to obtain the HF state.

[0025] In any aspect of the invention, the power supply may be configured to apply a set of additional DC voltages, referred to as compensation voltages ("(multiple) CVs" or just "CV"), to all segments simultaneously with the first set of voltage waveforms when the device is operating in FAIMS mode. For the avoidance of any doubt, the set of DC voltages (CVs) applied to the segments may include different DC voltages for different segments, i.e., the DC voltages applied to each segment need not be the same as the DC voltages applied to other segments (although in some examples where, for example, focusing is not required, the DC voltages may be the same as one another). As is known in the art, CVs select which ions pass through the analysis gap and may be fixed in time or scanned (gradually varying over time) to obtain a spectrum, as described, for example, in reference [5].

[0026] If the device is configured to provide focusing (see the second and third aspects of the invention discussed below), the electric field generated by applying CV to all segments preferably provides an electric field having substantially the same form as the electric field generated by applying the first set of voltage waveforms to the segments of the first segmented planar electrode and the second segmented planar electrode. The skilled person may directly implement CV to generate a field having such a form, for example via independently controlled power supplies or voltage dividers.

[0027] Preferably, the apparatus comprises a gas controller for controlling the gas pressure in the analysis gap.

[0028] The gas controller is configured to provide a gas pressure in the analysis gap such that the gas pressure in the analysis gap is lower in the transparency mode than in the FAIMS mode.

[0029] Preferably, the gas controller is configured to provide a gas pressure of 1-200 mbar, more preferably 5-100 mbar, more preferably 5-50 mbar in the analysis gap in FAIMS mode.

[0030] If the device is configured for separation of multiply charged proteins, the pressure controller may be configured to provide a gas pressure of 1-20 mbar in the analysis interval in FAIMS mode.

[0031] Preferably, the gas controller is configured to control the gas supply to the analysis gap so that the analysis gap contains a gas mixture. The gas mixture may include two or more of N2, H, He. The gas mixture may be He and N2, or H and N2.

[0032] Preferably, the pressure controller is configured to provide a gas pressure of 20 mbar or less, more preferably 10 mbar or less, more preferably 5 mbar or less, in the analysis gap in transparent mode. (The gas pressure may be different and is preferably lower than that used for FAIMS mode).

[0033] Preferably, the first set of voltage waveforms repeats at a first frequency, and the second set of voltage waveforms repeats at a second frequency. Preferably, the first frequency is lower than the second frequency.

[0034] The first frequency may be in the range of 5 kHz to 5 MHz, in the range of 10 kHz to 1 MHz, or in the range of 25 kHz to 500 kHz.

[0035] The second frequency may be 500 kHz or higher, may be 1 MHz or higher, may be 2 MHz or higher, may be 3 MHz or higher.

[0036] Preferably, the first voltage waveform and the second voltage waveform are substantially rectangular.

[0037] The power supply may be a digital power supply. This is a particularly convenient way of allowing the first and second voltage waveforms to have different frequencies and to be substantially rectangular waveforms (see above).

[0038] The device is preferably configured to operate in FAIMS mode with a duty cycle less than or greater than 0.5.

[0039] The power supply may be configured to apply a first set of voltage waveforms to segments of the first and second segmented planar electrodes by generating one or more RF voltage waveforms and applying the RF voltage waveforms to segments of the first and second segmented planar electrodes via an arrangement of capacitive voltage dividers.

[0040] The power supply can be configured to apply a second set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode by generating one or more RF voltage waveforms and applying the RF voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode (e.g., directly to the segments) without using an arrangement of capacitive voltage dividers.

[0041] The power supply is preferably configured to change the frequency of the segmented voltage waveform applied to the segmented planar electrode from a first frequency value to a second frequency value substantially instantaneously. In this article, substantially instantaneously can mean that this change occurs within one cycle of the voltage waveform before the frequency change (i.e. within 1 / f1, where f1 is the first frequency value). This can be most conveniently achieved if the power supply is digitally controlled. The power supply can be configured to change the frequency from a first frequency value to a second frequency value according to user input (e.g., via software).

[0042] The power supply is preferably configured to change the f-value of the segmented voltage waveform applied to the segmented planar electrode from the first f-value to the second f-value substantially instantaneously. In this article, substantially instantaneously can refer to that this change occurs within a cycle of the voltage waveform before the f-value changes. If the power supply is digitally controlled, this can be most conveniently achieved. The power supply can be configured to change the f-value from the first f-value to the second f-value according to user input (e.g., via software).

[0043] Preferably, the second set of voltage waveforms applied to the segments of the first and second segmented planar electrodes in transparent mode generates a quadrupole field within the analysis gap in a plane orthogonal to the analysis axis of the device to focus ions towards the analysis axis. Other forms of confining fields will be apparent to the skilled person.

[0044] The second voltage waveform (applied to the segments when the device operates in transparent mode) may have a duty cycle of 0.5 (f value = 1).

[0045] Preferably, the first segmented planar electrode and the second segmented planar electrode are arranged on opposite sides of the analysis gap.The first plane and the second plane are preferably parallel.

[0046] In this article, the analysis gap preferably extends in each of the gap height direction, the gap width direction and the gap length direction. The segments of the first segmented planar electrode and the second segmented planar electrode are preferably distributed in the gap width direction and extend in the gap length direction. The first segmented planar electrode and the second segmented planar electrode are preferably separated from each other in the gap height direction. The gap length direction is preferably parallel to the analysis axis.

[0047] The height of the analysis gap in the gap height direction (d g ) may be referred to herein as gap height or simply "g".

[0048] The width of the analysis gap in the gap width direction (d w ) may be referred to herein as gap width or simply "w".

[0049] The length of the analysis gap in the gap length direction (d l) may be referred to herein as the gap length or simply "l".

[0050] In some embodiments, w≥3 g. In some embodiments, w≥4 g.

[0051] If the first plane and the second plane are parallel, the gap height direction preferably extends in a direction perpendicular to the first plane and the second plane, the gap width direction preferably extends in a direction parallel to the first plane and the second plane and perpendicular to the analysis axis, and the gap length direction preferably extends in a direction parallel to the first plane and the second plane and parallel to the analysis axis. Therefore, the gap height direction, the gap width direction, and the gap length direction are preferably orthogonal to each other.

[0052] In theory, any number of segments is possible, but preferably, the device comprises 100 segments or less, more preferably 50 segments or less, more preferably 20 segments or less, more preferably 5 to 15 segments. At least 5 segments are preferred, but a higher number enables higher focus intensity values ​​(e.g., parameterized by the R2 / R1 ratio, as discussed below).

[0053] The propulsion component may be a gas supply configured to provide a gas flow to propel the ions through the analysis gap in a direction parallel to an analysis axis of the device.

[0054] The propulsion component can be a power supply configured to apply a voltage waveform to one or more electrodes of the device (which may, for example, include segments of a first segmented planar electrode and a second segmented planar electrode) in a second direction w to provide an electric field for propulsing ions through the analysis gap in a direction parallel to the analysis axis of the device.

[0055] A second aspect of the present invention provides:

[0056] An apparatus for performing field asymmetric waveform ion mobility spectrometry (FAIMS), the apparatus comprising:

[0057] a first segmented planar electrode comprising three or more segments, wherein the segments of the first segmented planar electrode are arranged in a first plane and extend in a direction parallel to an analysis axis of the device;

[0058] a second segmented planar electrode comprising three or more segments, wherein the segments of the second segmented planar electrode are arranged in a second plane and extend in a direction parallel to an analysis axis of the device, wherein the first segmented planar electrode and the second segmented planar electrode are separated from each other to provide an analysis gap therebetween;

[0059] a propulsion member for propulsing ions through the analysis gap in a direction parallel to an analysis axis of the device; and

[0060] power supply;

[0061] wherein the apparatus is configured to operate in a FAIMS mode, in which the power supply applies a set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component;

[0062] wherein the set of voltage waveforms is configured so that the asymmetric time-dependent electric field has contour lines of equal field strength when viewed in a plane perpendicular to the analysis axis, so that ions with different differential mobilities are focused toward different spatial domains, wherein each spatial domain extends along a corresponding contour line of equal field strength when viewed in a plane perpendicular to the analysis axis;

[0063] The device has a focus controller configured to allow a user to change the curvature of contour lines of equal field strength to change the focusing intensity provided by the asymmetric time-dependent electric field.

[0064] In this way, the strength of the focus provided by the asymmetric time-dependent electric field (or "focusing strength") can be controlled by the user to trade off the proportion of ions transmitted by the device versus the resolution provided by the device. As in all prior art devices, the higher the proportion of ions transmitted by the device, the lower the resolution, and vice versa.

[0065] A skilled person can understand from the disclosure herein that contour lines of equal field strength will connect positions of equal field strength, but different contour lines will represent different field strengths.

[0066] In this context, "strength of focusing" (or "focusing strength") may be understood to mean the extent to which ion losses occurring in a FAIMS separation can be reduced or prevented. These losses may be due to 1) diffusion and 2) space charge repulsion. Focusing preferably acts in the direction of the analytical gap g. In LP-FAIMS, focusing is particularly useful because diffusion (at constant temperature) decreases with increasing Increases and is proportional to the mobility k. This is because higher focusing strengths cause ions to focus into a tighter domain. A device with focusing capability obtains a higher transmittance than a device without focusing capability. A device with variable focusing capability allows the transmittance to be optimized to meet the given requirements of the resolution of FAIMS separation. Since some FAIMS applications only require moderate resolution, variable focusing capability allows higher transmittance.

[0067] In this context, "differential mobility" may be understood as the difference in ion mobility k between two different applied E / N values. In the FAIMS mode of the device, there are generally two E / N values ​​during the asymmetric time-correlated waveform: (1) an E / N value (E) that dominates during the high field voltage portion of the asymmetric time-correlated waveform. D / N) and (2) the E / N value that dominates during the low field voltage portion. In DMS, E D The value of E / N should be high enough to give K(E / N) a nonlinear dependence. The difference K(E / N) is therefore the basis for selection or separation in DMS.

[0068] For the avoidance of any doubt, FAIMS mode need not be the only operating mode of the device.

[0069] Preferably, the curve contours of equal field strength correspond to the electric field generated in the space between two coaxial cylindrical electrodes, wherein the outer radius of the inner cylindrical electrode is R1 and the inner radius of the outer cylindrical electrode is R2.

[0070] Such a field may be referred to herein as a "cylindrical field". Such a field may be generated by applying appropriately scaled asymmetric RF voltages and DC voltages to segments of the first segmented planar electrode and the second segmented planar electrode. In some embodiments, there may be a third segmented planar electrode and a fourth segmented planar electrode as described below, for example, to form a closed rectangular area. Any cylindrical field has a corresponding R2 / R1 value. It should be understood that R1 and R2 refer to electrodes that will produce an equivalent (i.e., mathematically indistinguishable from the electric field generated (regenerated) using the analysis gap of the FAIMS device) electric field. For clarity, the ratio of R2 / R1 directly determines the intensity of the focus. For the above arrangement of two coaxial cylindrical electrodes, the change in the electric field on both sides of the gap is E1 / E2=R2 / R1, where E1 is the electric field at the inner cylindrical electrode, and E2 is the electric field at the outer cylindrical electrode (note that with respect to the segmented planar FAIMS device, the inner cylindrical electrode and the outer cylindrical electrode are virtual). The absolute values ​​of R1 and R2 are not critical in terms of focusing strength and only affect the scale of the device, the invention being applicable to any practical scale.

[0071] Preferably, the focus controller is configured to allow a user to vary the R2 / R1 ratio of the cylindrical electric field in the analysis gap of the FAIMS device, for example via software.

[0072] Preferably, the first segmented planar electrode and the second segmented planar electrode are arranged on opposite sides of the analysis gap.

[0073] Preferably, the device further comprises:

[0074] a third segmented planar electrode comprising two or more segments, wherein the segments of the third segmented planar electrode are arranged in a third plane and extend in a direction parallel to an analysis axis of the device;

[0075] a fourth segmented planar electrode comprising two or more segments, wherein the segments of the fourth segmented planar electrode are arranged in a fourth plane and extend in a direction parallel to an analysis axis of the device;

[0076] wherein the first segmented planar electrode and the second segmented planar electrode are arranged on opposite sides of the analysis gap and are separated from each other in a gap width direction perpendicular to the analysis axis;

[0077] Wherein, the third segmented planar electrode and the fourth segmented planar electrode are arranged at opposite sides of the analysis gap and are separated from each other in a gap height direction perpendicular to the analysis axis and the gap width direction.

[0078] The use of a third and fourth segmented planar electrodes is a convenient way to provide a cylindrical field (particularly in devices with w<~8g), but a cylindrical field can also be achieved using only two segmented planar electrodes of sufficient length (for example in devices with w>8g).

[0079] The first plane and the second plane may be parallel to each other.The third plane and the fourth plane may be parallel to each other.

[0080] Preferably, the apparatus comprises a gas controller for controlling the gas pressure in the analysis gap and optionally comprises a chamber in which the segmented planar electrode of the FAIMS apparatus is located.

[0081] Preferably, the gas controller is configured to maintain the gas pressure constantly at a desired pressure.

[0082] Preferably, the gas controller is configured to provide a gas pressure of 1-200 mbar, more preferably 5-100 mbar, more preferably 5-50 mbar in the analysis gap in FAIMS mode.

[0083] The device may comprise a barrier having an exit slit, wherein the barrier is located on the analysis axis such that the propulsion means propels the ions towards the barrier, wherein the barrier is configured to prevent the ions from reaching a detector of the device unless they pass through the exit slit. For the avoidance of any doubt, the barrier and the exit slit may be located beyond the analysis gap, i.e. beyond the plane of the electrodes, optionally beyond any clamping electrodes (if present), e.g. in the direction of the length of the gap.

[0084] The barrier may be a physical barrier or an electrically resistive barrier (eg, provided by two or more Bradbury Nielsen doors, which are well known in the art).

[0085] The exit slit (in the gap height direction) may have a width w slit Width.

[0086] (e.g. if the device is to be used in transparent mode / in the case where the device is to be used in transparent mode, e.g. if the device is configured according to the first aspect of the invention) the barrier may be configured to be removed. If the barrier is a physical barrier, this may be achieved, for example, by a device configured to allow the barrier to be physically removed, for example using a motor (e.g. a linear motor). If the barrier is a resistive barrier, this may be achieved, for example, by configuring the resistive barrier to be closed.

[0087] The device may be configured to allow adjustment of the width of the exit slit provided by the barrier. If the barrier is a physical barrier, this may be achieved, for example, by providing a device with a plurality of barriers having exit slits of different widths that can be used interchangeably. If the barrier is a resistive barrier, this may be achieved, for example, by configuring the resistive barrier to allow adjustment of the width of the exit slit provided by the resistive barrier (for example, by supplying different voltages to the resistive barrier) (where the resistive barrier may be provided, for example, by two or more Bradbury Nielsen doors).

[0088] In this aspect of the invention, the(r) exit slit(s) preferably has a curvature corresponding to the curvature of contours of equal field strength of the asymmetric time-dependent electric field, viewed as a curve in a plane perpendicular to the analysis axis.

[0089] The device may be configured to allow adjustment of the curvature of the exit slit provided by the barrier. If the barrier is a physical barrier, this may be achieved, for example, by providing a device with a plurality of barriers having exit slits of different curvatures that can be used interchangeably. If the barrier is a resistive barrier, this may be achieved, for example, by configuring the resistive barrier to allow adjustment of the curvature of the exit slit provided by the resistive barrier (for example, by supplying different voltages to the resistive barrier) (where the resistive barrier may be provided, for example, by two or more Bradbury Nielsen doors).

[0090] The device can be configured to allow the curvature of the exit slit provided by the barrier to be adjusted to a curvature corresponding to the curvature of contours of equal field strength of the asymmetric time-dependent electric field viewed as curved in a plane perpendicular to the analysis axis, after changing the curvature using a focus controller.

[0091] For the avoidance of any doubt, the focus controller may be implemented in software or hardware.

[0092] The device of this aspect of the invention may have any feature or combination of features described in conjunction with the first aspect of the invention.

[0093] Preferably, the power supply is configured to apply corresponding voltage waveforms from a set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap when the apparatus is operating in FAIMS mode.

[0094] Preferably, the power supply comprises two power supply units configured to apply corresponding voltage waveforms from a set of voltage waveforms to each segment of the first segmented planar electrode and the second segmented planar electrode when the apparatus is operating in FAIMS mode to generate an asymmetric time-dependent electric field in the analysis gap.

[0095] Herein, the first power supply unit in the power supply unit may be configured to supply a dispersed voltage (eg, hereinafter designated as V D / 2 and -V D / 2), and the second power supply unit in the power supply unit may be configured to supply a focus voltage (eg, designated as V fp and V fn ), wherein the device includes one or more capacitive voltage dividers so that different voltages are applied to different segments (e.g., as required by a particular geometry). In this way, the necessary voltage waveform can be provided efficiently. Figure 3A Let's discuss examples.

[0096] The power supply may be configured to apply a set of additional DC voltages, referred to as compensation voltages ("CV(s)" or just "CV"), to all segments simultaneously with the first and second sets of voltage waveforms.

[0097] The CV may have a predetermined value configured to cause ions having a predetermined differential mobility to exit through the exit slit (eg, as described above).

[0098] The apparatus may be configured to scan the CV so that ions with different predetermined differential mobilities exit through the exit slit at different times, for example to provide a differential ion mobility spectrum.

[0099] If the power supply is configured to apply CV to all segments simultaneously with applying a set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode, the electric field generated by applying CV to all segments preferably provides an electric field having substantially the same form as the electric field generated by applying a set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode.

[0100] In any aspect of the invention, the device may include a detector configured to detect ions passing through the analysis gap in a direction parallel to an analysis axis of the device.

[0101] A third aspect of the present invention provides:

[0102] An apparatus for performing field asymmetric waveform ion mobility spectrometry (FAIMS), the apparatus comprising:

[0103] a first segmented planar electrode comprising three or more segments, wherein the segments of the first segmented planar electrode are arranged in a first plane and extend in a direction parallel to an analysis axis of the device;

[0104] a second segmented planar electrode comprising three or more segments, wherein the segments of the second segmented planar electrode are arranged in a second plane and extend in a direction parallel to an analysis axis of the device, wherein the first segmented planar electrode and the second segmented planar electrode are separated from each other to provide an analysis gap therebetween;

[0105] a propulsion member for propulsing ions through the analysis gap in a direction parallel to an analysis axis of the device; and

[0106] power supply;

[0107] wherein the apparatus is configured to operate in a FAIMS mode, wherein in the FAIMS mode, the power supply applies a first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component;

[0108] In which, the first set of voltage waveforms is configured so that the asymmetric time-correlated electric field has essentially linear contour lines of equal field strength when viewed in a plane perpendicular to the analysis axis, so as to focus ions with different differential mobilities toward different spatial domains, wherein each spatial domain extends along a corresponding linear contour line of equal field strength when viewed in a plane perpendicular to the analysis axis.

[0109] In this way, the inventors have discovered that it is possible to simultaneously have high transmittance and high resolution when the device includes a barrier as described below.

[0110] Preferably, the apparatus has a focus controller configured to allow a user to change the gradient of contours of isofield strength (e.g. calculated at predetermined positions in the analysis gap) to change the focus strength provided by the asymmetric time-dependent electric field (e.g. calculated at predetermined positions). Note: In general, changing the gradient of contours of isofield strength at one position in the analysis gap will result in similar changes in the gradients of contours of isofield strength at other positions in the analysis gap.

[0111] In this way, where the device includes a barrier as described below, the strength of the focusing provided by the asymmetric time-dependent electric field (or "focusing strength") can be controlled by the user without having to trade off the ratio of ions transmitted by the device versus the resolution provided by the device. In general, the higher the ratio of ions transmitted by the device, the lower the resolution, and vice versa.

[0112] At a given position in the analysis gap, the gradient of the contours of equal field strength can be approximated as the difference of the electric field with respect to the distance in the direction of the gap height. This corresponds to the difference of the electric field strength at the two closest points on two contours of equal field strength divided by the distance between these points in the direction of the gap height.

[0113] The device may comprise a barrier having an exit slit, wherein the barrier is located on the analysis axis such that the propulsion means propels the ions towards the barrier, wherein the barrier is configured to prevent the ions from reaching a detector of the device unless they pass through the exit slit. For the avoidance of any doubt, the barrier and the exit slit may be located beyond the analysis gap, i.e. beyond the plane of the electrodes, optionally beyond any clamping electrodes (if present), e.g. in the direction of the length of the gap.

[0114] The barrier may be a physical barrier or an electrically resistive barrier (eg, provided by two or more Bradbury Nielsen doors, which are well known in the art).

[0115] The exit slit (in the gap height direction) may have a width w slit Width.

[0116] (e.g. if the device is to be used in transparent mode / in the case where the device is to be used in transparent mode, e.g. if the device is configured according to the first aspect of the invention) the barrier may be configured to be removed. If the barrier is a physical barrier, this may be achieved, for example, by a device configured to allow the barrier to be physically removed, for example using a motor (e.g. a linear motor). If the barrier is a resistive barrier, this may be achieved, for example, by configuring the resistive barrier to be closed.

[0117] The device may be configured to allow adjustment of the width of the exit slit provided by the barrier. If the barrier is a physical barrier, this may be achieved, for example, by providing a device with a plurality of barriers having exit slits of different widths that can be used interchangeably. If the barrier is a resistive barrier, this may be achieved, for example, by configuring the resistive barrier to allow adjustment of the width of the exit slit provided by the resistive barrier (for example, by supplying different voltages to the resistive barrier) (where the resistive barrier may be provided, for example, by two or more Bradbury Nielsen doors).

[0118] In this aspect of the invention, the(r) exit slit(s) are preferably linear and extend in a direction corresponding to contours of isofield strength of the asymmetric time-dependent electric field which appear linear in a plane perpendicular to the analysis axis.

[0119] The piecewise planar FAIMS device, configured so that the asymmetric time-dependent electric field has substantially straight contours of equal field strength as seen in a plane perpendicular to the analysis axis, combined with the linear exit slit eliminates the trade-off between resolution and transmittance suffered by all FAIMS and DMS devices to date. Thus, higher resolution can be achieved together with high transmittance. The highest resolution can be achieved at the highest focus intensity.

[0120] Furthermore, the essentially straight contours of equal field strength imply that the slit shape is independent of the focusing intensity.

[0121] Substantially straight contours of equal field strength are preferably substantially straight over a significant distance (eg, over a distance of w / 4 or more).The skilled person will appreciate that substantially straight contours of equal field strength are difficult to achieve perfectly.

[0122] The power supply may be configured to apply a set of additional DC voltages, referred to as compensation voltages ("CV(s)" or just "CV"), to all segments simultaneously with the first and second sets of voltage waveforms.

[0123] The CV may have a predetermined value configured to cause ions having a predetermined differential mobility to exit through the exit slit (eg, as described above).

[0124] The apparatus may be configured to scan the CV so that ions with different predetermined differential mobilities exit through the exit slit at different times, for example to provide a differential ion mobility spectrum.

[0125] If the power supply is configured to apply CV to all segments simultaneously with applying a set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode, the electric field generated by applying CV to all segments preferably provides an electric field having substantially the same form as the electric field generated by applying a set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode.

[0126] The height of the analysis gap in the gap height direction may be referred to herein as the gap height or simply "g".

[0127] The ratio of gap width to gap height (w / g) may be in the range of 2 to 6, more preferably in the range of 3 to 5, more preferably in the range of 3.5 to 4.5, and may be about 4. This limitation may be preferred if the device includes (as discussed elsewhere) a third segmented planar electrode and a fourth segmented planar electrode, but this preference does not apply if the device does not include a third segmented planar electrode and a fourth segmented planar electrode.

[0128] The device of this aspect of the invention may have any feature or combination of features described in conjunction with the first aspect of the invention.

[0129] The device of this aspect of the invention may have any feature or combination of features described in conjunction with the second aspect of the invention.

[0130] Another aspect of the present invention provides an analytical device, the analytical device comprising:

[0131] An apparatus for performing FAIMS according to any of the preceding aspects of the invention;

[0132] Apparatus for performing mass spectrometry;

[0133] In which the device for performing mass spectrometry is configured to analyze ions that have passed through the analysis gap of the FAIMS device (in this case, the analysis device may be referred to as a "FAIMS / MS device"), or the device for performing FAIMS is configured to analyze ions that have been selected by the device for performing mass spectrometry (in this case, the analysis device may be referred to as a "MS / FAIMS device").

[0134] Other aspects of the present invention may provide a method of operating an apparatus for performing FAIMS according to any of the aforementioned aspects of the present invention.

[0135] The present invention includes any combination of described aspects and preferred features unless such a combination is expressly impermissible or explicitly avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0136] Embodiments and experiments illustrating the principles of the present invention will now be discussed with reference to the accompanying drawings, in which:

[0137] Figure 1 A FAIMS / MS apparatus comprising an exemplary LP-FAIMS apparatus is shown.

[0138] Figure 2A Figure 4 shows a typical FAIMS device comprising segmented planar electrodes.

[0139] Figure 3A C shows the typical voltage divider for operation in FAIMS mode and transparent mode. Figure 2A FAIMS PSU for FAIMS device of ~C.

[0140] Figure 4A B to B respectively show the application of harmonic and rectangular voltage waveforms used in the transparent mode.

[0141] Figure 5A ~B shows the characteristics of the cylindrical electric field.

[0142] Fig. 6A ~B shows another typical FAIMS device and typical equipotential.

[0143] Fig. 7A D shows the effect of a non-segmented planar LP-FAIMS operating in split mode with focusing (focusing is provided by contours of electric field strength) compared to a non-segmented planar LP-FAIMS without any electric field gradient or focusing. Fig. 6A ~B's FAIMS device.

[0144] Fig. 8A B to B respectively show the focusing provided by the cylindrical field in the split mode operation Fig. 6A FAIMS device of B and operating in separation mode with focusing provided by near linear field Fig. 6A ~B's FAIMS device.

[0145] Figures 9A to 9B A piecewise planar FAIMS device is shown in which all segments of each electrode carry equal potential.

[0146] Fig. 10A ~D show the isofield contours of different FAIMS device structures.

[0147] Fig.11A ~D shows a simulation of a piecewise planar LP-FAIMS device operating in transparent mode.

[0148] Fig.12 Shown are CV (DV) curves obtained from simulations of FAIMS separation mode without field gradient.

[0149] Fig.13Shown are resolution / sensitivity diagrams resulting from experiments performed using a planar LP-FAIMS setup (with and without a linear field gradient).

[0150] Fig.14A Figure ∼B shows further results obtained from experiments performed using a planar LP-FAIMS apparatus. DETAILED DESCRIPTION

[0151] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying drawings. Other aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated herein by reference.

[0152] In general, the present invention relates to possible configurations of differential ion mobility spectrometers and their possible use in conjunction with mass spectrometers. A particular use is in improving the operation of low pressure DMS devices.

[0153] In general, the following examples can be viewed as building on the teachings of reference [1] and helping to provide a FAIMS device with segmented planar electrodes and improved separation and transparency modes.

[0154] Context

[0155] In designing the present invention, the inventors constructed a prototype low-pressure FAIMS (LP-FAIMS) device as described in reference [1] using both the multipolar structure disclosed herein (in the form of electrode 26 in Figure 2 of reference [1]) and the (non-segmented) planar structure (in the form of electrode 20 in Figure 2 of reference [1]). The low pressure allows a significant widening of the analysis gap ("FAIMS gap") and a reduction in the waveform frequency and peak amplitude (dispersion voltage, "DV"). The lower frequency and lower peak amplitude DV allows the generation of DV waveforms by digital switching techniques, in particular, it allows the generation of nearly rectangular DV waveforms with widely variable frequency and duty cycle d (expressible as f values, where f = (1-d) / d, according to the definitions given above).

[0156] DV and compensation voltage (“CV”) in FAIMS are preferably expressed as scattered field (E D ) and compensation field (E C ) to adjust for the gap width. In LP-FAIMS, the electric field is preferably divided by the gas number density N (number of molecules per unit volume) to provide E D / N and E C / N, these quantities translate into reduced fields, which helps eliminate the dependence of the separation on gas pressure (except for large molecules that exhibit electric dipole alignment) and reduces the dependence of the separation on temperature. Low pressure allows higher E D / N value (usually limited by the electrical breakdown of the gas), thus enabling separation deep into the nonlinear IMS region. This improves resolution, thereby offsetting the peak broadening due to increased diffusion (the isotropic diffusion coefficient is expressed as P -1 / 2 The inventors have found that a planar gap structure can provide higher resolution than a multipole geometry.

[0157] It is suggested in the art to set the electrodes to different temperatures to form a constant temperature gradient (and hence gradient of N and E / N) across the analysis gap and to focus the ions being analyzed by FAIMS in the gap, see for example reference

[12] . As known in ambient pressure FAIMS technology, such a gradient will focus ions of the appropriate form of K(E / N) (ion mobility K is expressed as a function of E / N) to the gap median (gap median = half the gap along the gap height direction).

[0158] The inventors have realized a constant temperature gradient in the context of the present invention (i.e., planar LP-FAIMS). Herein, the inventors have found that applying a thermal gradient allows the maximum resolution to be increased to a maximum resolution in an equivalent planar gap device that exceeds the lack of a thermal gradient. Optimal performance requires regulating the gas pressure in the LP-FAIMS chamber while keeping the pressure in the downstream chamber constant. The inventors have also found that applying a thermal gradient also provides increased ion transmittance by reducing the ion loss on the electrode caused by diffusion and space charge expansion. Signal gain may be high (typically 4 times), but this gain is obtained at the expense of some resolution of FAIMS separation.

[0159] To this end, components were designed to quickly change and stabilize the pressure in the LP-FAIMS without affecting the pressure in the downstream chambers.

[0160] The inventors are not aware of other techniques for achieving a constant temperature gradient in a planar FAIMS device.

[0161] By market analysis, making FAIMS / MS technology mature to have wider acceptance depends on maximizing the ion transmittance by FAIMS level when there is no separation (that is, when " FAIMS is switched to close " in transparent mode). It is not an acceptable solution to carry out repeated physical removal and reinstallation of FAIMS device, because this is very time consuming, requires trained personnel, disrupts the workflow, usually needs to verify after each reinstallation, and will make the parts of these two units produce stress. It is also expected that the automatic acquisition capability that FAIMS open mode and FAIMS close mode (in a pre-programmed or data-dependent manner) are combined. Therefore, FAIMS should be designed as an instrumented component. Market analysis will also be unable to realize high resolution and high sensitivity identification as another problem simultaneously. For example, although FAIMS can eliminate chemical noise to improve the detection limit (LoD) of the kind for some chemical classes such as tryptic peptides, total ion loss limits the LoD gain.

[0162] Although the planar gap LP-FAIMS geometry of reference [1] provides better resolution than the above-mentioned multipoles, the present inventors have found that it does not effectively transmit ions when the FAIMS is turned off. Overcoming this limitation is one motivation for the present invention.

[0163] In other words, one problem to be solved is to provide a mode that effectively transmits all ions without discrimination or selection by differential mobility, while allowing rapid switching between this "transparent" mode and the FAIMS separation mode without mechanical adjustments (note that this problem needs to be overcome in a planar format rather than a square format as taught in Ref.

[13] ).

[0164] A known method for focusing ions in a planar FAIMS gap is to heat one electrode on top of the other electrode to establish a thermal gradient across the gap. The thermal gradient focuses the ions by resisting ion diffusion and space charge. This focusing technique is associated with several major problems, including four inherent to the method: (1) focusing only works in conjunction with FAIMS separation, preventing the desired FAIMS shutdown (no components exist for focusing ions in transparent mode); (2) the focusing intensity is strongly dependent on the K(E / N) characteristics of specific ions, some of which are poorly focused or actively defocused; (3) the heating gas couples the focusing to the intrinsic temperature dependence of the mobility and produces unpredictable results; and (4) heating may cause the ions to dissociate or isomerize. Two other problems are practical: (5) heating or cooling of the electrodes takes too long for fast switching to focus or adjust their intensity, preventing use in data-dependent acquisition mode and many other modes, and (6) the thermal gradient has an upper limit due to heat transfer across the gap, limiting the maximum focusing intensity. Although these problems can be partially addressed by further design, the cost and complexity will be very large. This situation motivated the present inventors to find a method to achieve ion focusing in a FAIMS device without manipulating the electrode temperature.

[0165] When designing the present invention, the inventors were trying to realize a FAIMS device, preferably a LP-FAIMS device, which has:

[0166] Two operating modes: Split mode and "transparent" mode

[0167] Improved ion transmission in transparent mode

[0168] Higher resolution in separation mode

[0169] Easily adjustable resolution / sensitivity balance in split mode

[0170] Improved resolution and sensitivity in separation mode

[0171] With respect to the prior art, FAIMS devices having a cylindrical gap (i.e., a gap between two cylindrical electrodes, see electrode 22 in FIG. 2 of reference [1]) or a dome-shaped gap (i.e., a gap between two hemispherical domes) are known to provide higher transmittance and lower resolution than planar gap devices (having a gap between two planar electrodes, see, for example, electrode 20 in FIG. 2 of reference [1]). This is because the non-uniform (cylindrical) electric field in the annular gap between the coaxial cylindrical electrodes focuses ions of the appropriate K(E / N) form into a domain corresponding to the K(E / N) value. The focusing intensity increases with increasing gap curvature, defined by the ratio R2 / R1, where R1 is the outer diameter of the inner electrode and R2 is the inner radius of the outer electrode.

[0172] Reference [2] teaches applying voltages to specific elements of a planar FAIMS electrode (having segments extending along the analytical axis, i.e., along the direction in which the ions travel through the gap) to form a substantially cylindrical electric field therebetween, and varying these voltages to tune the curvature of the intermediate equipotential surfaces. However, the purpose of the tuning is not specified, and no components are disclosed for achieving the tuning. In addition, the device taught in reference [2] does not provide components for focusing ions in a transparent mode. These problems are addressed by the present invention.

[0173] 1) The first aspect of the present invention

[0174] In the examples discussed below, this aspect of the invention may be viewed as providing a planar FAIMS device with an improved transmission mode.

[0175] The present invention relates to planar gap FAIMS (LP-FAIMS) in particular at deep sub-ambient gas pressures. Although we have investigated (in experiments and / or simulations) a pressure range of 5-100 mbar, this is limited by current instrumentation and sample aspects. A wider range of 1-200 mbar should be feasible.

[0176] Preferred features of this aspect of the invention:

[0177] 1. The electrode is divided into at least three segments that are elongated along the direction of ion travel through the gap. The resulting device may be referred to hereinafter as a segmented planar FAIMS.

[0178] 2. There is a propulsion component to propel the ions through the gap.

[0179] 3. The FAIMS power supply unit (PSU) has components to switch between a symmetrical waveform (50% duty cycle for transparent mode) and an asymmetrical waveform (duty cycle other than 50% (any desired value) for FAIMS mode).

[0180] 4. There are components for switching between two electric field configurations, e.g., (a) a basic dipole field for FAIMS separation and (b) a basic quadrupole field for ion confinement (transparent mode). As described herein (e.g., see discussion of Figure 3B , Figure 3C and Fig.11A ~D), various transparency modes are possible.

[0181] 5. The FAIMS PSU has components for switching between two substantially different RF frequencies (eg, because the optima for FAIMS separation and ion confinement in transparent mode are substantially different).

[0182] 6. There are means for switching the pressure between two stable values ​​(eg, because the optimal pressure for FAIMS separations usually exceeds the optimal pressure for optimal ion transmission in transparent mode).

[0183] In transparent mode, ions can permeate the gap without being intentionally selected or discriminated based on absolute or differential mobility, and with minimal losses due to diffusion and Coulomb expansion. In the example discussed below, the quadrupole field confines the ions to the mid-gap to increase their efficiency in passing through subsequent apertures to downstream stages.

[0184] In the experiment, the multipole device in reference [1] provides lower FAIMS resolution compared to the planar gap device, and no effective components are provided for tuning the ion focusing intensity. According to reference [1], ions move along the gap due to the airflow generated by various components or electric fields. Similar methods can be applied to the present invention. FAIMS devices with different focusing intensities are useful for many applications. For example, high sensitivity is very important when removing chemical interferences to improve the detection limit (sensitivity) in MS or to reduce the multiplicity of the charge state of protein ions. When sufficient samples are available, higher resolution is crucial for unraveling structural isomers (such as lipids or peptides).

[0185] The present invention eliminates the need to physically remove the LP-FAIMS device from a mass spectrometer or other instrument to restore its original performance by increasing the ion transmittance through the FAIMS stage to 100% in transparent mode. The present invention can be applied to LP-FAIMS devices having segmented planar electrodes and preferably operating at sub-ambient pressure, more preferably in the range of 1 to 200 mbar and most preferably in the range of 5 to 50 mbar. The gas component may be 100% nitrogen, or a mixture of helium and nitrogen. The inventors have found that in the context of LP FAIMS, a mixture of helium and nitrogen can significantly improve resolution and transmittance compared to 100% nitrogen. Other gas components may also be used (e.g., CO2 and hydrogen), without limitation.

[0186] 2) Second Aspect of the Invention

[0187] In the examples discussed below, this aspect of the invention can be viewed as providing a practical planar FAIMS device with variable focus strength, improved transmittance and improved resolution.

[0188] Two types of FAIMS device geometries are known in the art: (i) a curved (particularly cylindrical) gap established using coaxial cylindrical and / or concentric spherical electrodes; and (ii) a planar gap established using parallel planar electrodes. Planar gap FAIMS has been found to provide the highest resolution at the expense of ion transmittance (sensitivity). The key metric for cylindrical FAIMS that controls the intensity of the focus is the gap curvature as defined above. FAIMS Pro (an existing product of Thermo Corporation) uses R2 / R1=1.2 to achieve strong focusing, thereby achieving near-maximum ion transmittance. Other commercial FAIMS and FAIMS-MS systems, particularly the Lonestar FAIMS (Owlstone) and SelexIon FAIMS / MS (Sciex) derived from stand-alone systems (legacy Sionex), use planar gap devices.

[0189] All of these FAIMS devices operate at ambient pressure. The SelexIon system has a short ion residence time to limit ion losses, but still provides higher resolution than the FAIMS pro. The upper limit of the resolving power achieved so far by planar ambient pressure FAIMS is about 150 for single charge and about 400 for multiply charged species (see reference [6]), but with very limited ion penetration / sensitivity.

[0190] Reference [1] teaches methods for operating FAIMS at low gas pressure (i.e., "LP-FAIMS"). Subsequently, LP-FAIMS was demonstrated using planar and multipole geometry cells coupled to quadrupole or time-of-flight mass spectrometry (e.g., reference [7]). Typical separations using planar gap cells include separations of nominal isobaric amino acids (representing small molecule applications) and PTM localization variants of mono- and di-phosphorylated peptides from human tau protein (representing frontier proteomics and epigenetic analysis). Resolution is generally comparable to or exceeds the resolution of commercial ambient pressure FAIMS systems configured for reasonable ion penetration, but does not reach the resolving power of high-resolution FAIMS systems. However, the ion residence time in these studies was approximately 10 ms, compared to ion residence times of approximately 100 to 500 ms for high-resolution FAIMS. The short filtration time is useful because it allows the FAIMS scan to be nested within a reasonable peak elution time in a preceding liquid chromatography (LC) or capillary electrophoresis (CE) separation.

[0191] As explained above, the electric field in LP-FAIMS is preferably expressed in terms of a constant E / N, with the unit being Townsend (Td). C / N vs. E D The dependence of E / N and the K(E / N) function derived therefrom are suitably independent of pressure and electric field strength alone.

[0192] The ability to access the highly nonlinear K(E / N) region at low pressures provides additional separation flexibility and higher resolution.

[0193] As previously described, digital switching, which can be achieved by operating the FAIMS device at low pressure, is capable of producing near-rectangular waveforms with widely variable frequencies and HF / LF ratios (expressed as f-values), and the ability to rapidly change frequency and amplitude. (While the technique can be used at any pressure, practical power consumption and dissipation constraints limit it to the low voltage range, thus narrowing the gap at ambient pressure, resulting in low resolution.) Energy recovery digital PSU technology is preferred for reducing power consumption.

[0194] The use of thermal gradients to focus ions in FAIMS has been suggested for ambient pressure plane FAIMS as described above, and has been demonstrated for LP-FAIMS in (unpublished) studies by the inventors. The inventors have recognized that the focusing conditions resulting from variations in N (via the local gas temperature T) or E are different. The former involves a constant E / N gradient, but the intrinsic K(T) dependence superimposed thereon (depending on ion species and gas identity) produces complex case-specific behavior. The latter (in curved gaps) involves a non-constant E / N gradient, where E scales with 1 / R in cylindrical gaps, or with 1 / R in spherical gaps. 2 Scaling. Therefore, the two methods are not equivalent, and the effective gradient is non-linear in both methods. As described above, establishing an E / N gradient by thermal variation has a variety of disadvantageous inherent and practical aspects. A true linear E / N gradient could bring huge operational benefits, but may not be found in the known prior art.

[0195] This aspect of the invention can be viewed as providing a substantially linear E / N gradient using segmented planar electrodes. While this is possible in principle at any gas pressure, it is best suited for LP-FAIMS because physically larger electrodes facilitate mechanical implementation, while lower voltages and frequencies simplify electrical engineering. Furthermore, the transparent mode is not available at atmospheric pressure.

[0196] Preferred features of this aspect of the invention:

[0197] 1. Working pressure range is 1~200mbar.

[0198] 2. The LP-FAIMS device has two planar electrodes, each planar electrode comprising at least three segments extending along the direction in which ions travel through the gap. The two electrodes may be separated by a dielectric spacer.

[0199] 3. There are components to propel ions through the gap.

[0200] 4. The PSU is capable of outputting at least four asymmetrical waveforms.

[0201] 5. There are at least two asymmetric waveforms with a duty cycle of d and at least one asymmetric waveform with a duty cycle of (1-d).

[0202] 6. Supply at least some of the four asymmetric waveforms and dc voltage (to establish CV value) to produce a cylindrical electric field with adjustable focusing intensity.

[0203] 7. There are components to quickly adjust and stabilize the pressure in the LP-FAIMS unit.

[0204] 8. There are means to determine the ion filtering time in the FAIMS gap (this can be achieved by adjusting the device length, or by adjusting the jet drive flow by physically exchanging the gas shaping pipes before the FAIMS device).

[0205] The present invention is based not only on reference [2], but also on aspects other than the teachings of reference [2]. Specifically, reference [2] teaches applying a voltage to produce a cylindrical field with a variable effective radius. However, reference [2] does not envision or teach the objective and the method for achieving the objective. The inventors have found that the focusing intensity is directly related to the ratio of the maximum field radius to the minimum field radius on both sides of the gap (R2 / R1), where the absolute field radius is not important to the focusing intensity.

[0206] The cylindrical electric field generated by the voltage on the electrode segments is equivalent to the electric field in a physical cylindrical gap. The focusing strength in piecewise planar LP-FAIMS can be tuned by varying the electrode voltages to produce a field with a desired effective R2 / R1 value, which can be set to be independent of the gap width (g). However, in this case, the focusing domain (the spatial domain toward which ions with a given differential mobility are focused) is smaller for stronger focusing strengths (i.e., higher E on either side of the gap). D / N gradient) has an arc of increasing curvature. If there is no such gradient, then E C / N depends on E D / N, because:

[0207]

[0208] Among them, α 1 , α 2 , α 3 is the "α coefficient" that describes the nonlinear migration behavior. The terms F2 to F7 depend on the waveform distribution; for example, for an ideal rectangular waveform with an f value of 4, the terms F2 to F7 are 0.25, 0.188, 0.203, 0.199, 0.200 and 0.200, respectively. For a field gradient (such as in a cylindrical FAIMS), equation (1) is satisfied at a specific (equilibrium) radius. Ions displaced to a lower or higher radius experience a restoring force toward the radius, which means a stable equilibrium. This focusing effect suppresses (anisotropic longitudinal) diffusion in the radial direction where separation occurs. The field gradient with E caused by the voltage on the electrode segment D / N gradient in the plane gap, will suppress the bending E D / N isosurfaces orthogonal to diffusion. However, the (lateral) diffusion along these faces is still free, making the ion group become more and more curved as the separation proceeds. The variation of the applied CV will scan the entire ion group across the gap, thereby allowing ions to pass through the FAIMS device within the range of CV values. As known in the art with a physical curved gap, this will expand the peak in the CV spectrum, thereby reducing the resolution of the separation.

[0209] For sufficiently accurate cylindrical fields in piecewise planar FAIMS, the lateral electrode span (w) should exceed g (the width of the FAIMS gap) by about an order of magnitude. The fringing electric fields near the electrode edges will then not have a substantial effect on the electric fields near the device axis (in the region occupied by ions traveling along the gap).

[0210] If reasonable focusing strength is required, a wide gap may make it difficult to generate the required voltage.

[0211] For a completely closed gap (e.g., having a first segmented planar electrode, a second segmented planar electrode, a third segmented planar electrode, and a fourth segmented planar electrode) with appropriate voltages applied to all electrodes, the necessary w / g ratio may be reduced. The segment width may vary across the electrode span, increasing from the axial edge.

[0212] 3) The third aspect of the present invention

[0213] In the examples discussed below, this aspect of the invention can be viewed as providing a planar FAIMS device with variable focus strength and improved resolution combined with improved transmittance.

[0214] In this regard, the segment voltage can be adjusted to produce a near-linear gradient of E in a fairly large volume around the median of the gap and the axis of the gap, where E D And therefore E D The isosurface of the basic plane of / N is parallel to the electrodes and offsets toward any electrode according to the applied CV. The voltage required for any electrode geometry can be obtained by numerical iteration. The method used for this calculation is standard and can be implemented by a person skilled in the art according to the present invention. According to the numerical calculations and modeling of the inventors, the optimal w / g ratio used in the examples in this aspect of the invention is about 4. The field relaxation of the open gap provides a sufficiently linear E in the median region of the device. D / N isosurfaces. This is an example used to conveniently generate suitable linear field gradients, but other methods may be used.

[0215] In this way, ions are constrained to planar layers around these surfaces and can diffuse in such layers. However, the focused ion group will now be nearly planar, and only a monolayer with a characteristic CV can pass through the planar gap and leave the unit through a narrow hole (preferably a slit in the gap plane) to a downstream mass spectrometer or other instrument level. The hole should be shaped and positioned so as not to disturb the FAIMS separation field, and is preferably removable or adjustable to allow a "transparent" mode. The hole can be used in conjunction with an electrode that clamps the edge field (limits the range of the edge field), and it can also be used to accelerate ions through a region of significant edge field near the cell outlet. In the case where ions are carried across the gap by the airflow, the slit should not have a substantial effect on the flow distribution. In some embodiments, the barrier can be formed by a wire electrode that operates as a Bradbury Nielsen gate. The ions are stopped because of the two-phase RF applied to the gate and are allowed to pass because the RF is removed. The effective width of the gap can also be adjusted by controlling the RF applied to the Bradbury Nielsen gate. This arrangement has the advantage that the apertures do not need to be physically removed, but can be opened or closed quickly in a predetermined manner and without significantly disrupting the airflow leaving the device.

[0216] The higher the focusing strength, the thinner the slit should be.

[0217] Preferred features of this aspect of the invention include features 1 to 5, 7 and 8 discussed above in conjunction with the second aspect of the invention, plus:

[0218] 9. At least some of the four asymmetric waveforms and dc voltages supplied (to establish CV values) have independently variable amplitudes to produce an electric field with substantially planar isosurfaces parallel to the planar electrodes. Note: This is not a direct change, but will require a change in the way the voltage is divided between segments to obtain a linear field gradient. It is doubtful that this change can be achieved by simply changing 4 voltages.

[0219] 10. The apparatus may comprise a barrier having an exit slit, wherein the barrier is located on the analysis axis such that the propulsion member propels the ions towards the barrier, wherein the barrier is configured to prevent the ions from leaving the analysis gap unless they pass through the exit slit.

[0220] This aspect of the invention relates to FAIMS with any mechanism for propelling ions through the gap in all of the methods described in reference [1], including flow drive, longitudinal field drive or jet drive. Ion focusing in FAIMS allows for use in conjunction with extended (i.e., extended by making the device longer) filtration times without the ion losses that typically accompany beam broadening due to diffusion or Coulomb repulsion, thereby enabling improved resolution and more moderate ion losses.

[0221] When using a barrier with slits in combination with strong focusing, the present invention produces good transmission combined with high resolution and short filtration time.

[0222] Detailed Example

[0223] 1) Regarding the first aspect of the present invention

[0224] Figure 1 A FAIMS / MS apparatus 1 comprising an exemplary LP-FAIMS apparatus 14 is shown.

[0225] refer to Figure 1 , chamber 6 including LP-FAIMS device 14 is located between an atmospheric pressure ionization (API) ion source (in this example, an electrospray ionization (ESI) source 2) and an MS stage 8. As is known in the art, a sample in a suitable solvent is delivered to 2, which produces a plume of charged droplets. The droplets and at least some of the ions released therefrom enter a desolvation tube (capillary) 4, where the droplets evaporate and release ions. The ions are entrained in a supersonic gas jet that leaves 4 and enters chamber 6 and is maintained at a pressure of 1 to 100 mbar. Chamber 6 includes components for slowing the jet (as disclosed in reference [1]). Device 14 allows all ion species or a subset thereof having selected differential mobility values ​​to pass through to a skimmer 16, while other species are deflected toward the FAIMS electrode and destroyed by neutralization when they fall on the surface of the FAIMS electrode.

[0226] Figure 2A The typical segmented FAIMS device shown includes two parallel planar electrodes, with segments 18a-18k in the upper electrode and 20a-20k in the lower electrode. Figure 2A Also shown is the gap height (d g ) direction, gap width (d w ) direction and gap length (d l ) direction. Each electrode may include three or more segments (e.g., up to one hundred segments), the current depiction showing eleven segments. Figure 2B A cross section of a device with typical dimensions of g = 7.5 mm and w = 30 mm (here w = 4g) is presented. L-shaped segments with a 2 mm lateral span, 0.5 mm gap, are fixed in mountings separated by insulating spacers and separated by insulating spacers. Figure 2C As shown, the upper and lower electrodes are separated by two insulating spacers 30 which define the g value.

[0227] Describe in more detail Figure 3AThe voltages illustrated for the cylindrical (focusing) field can be provided by only two PSUs for all the electrode segments in the two planes of segmented electrodes (electrodes p1 to p11 and n1 to n11 in the example). The two PSUs can then provide the required voltages to each electrode segment in the electrodes of the planes. For each electrode segment, there is a voltage supply denoted as V D / 2 and -V D / 2 dispersion voltage and focusing voltage V fp and V fn The subscript fp represents a positive focus voltage and fn represents a negative focus voltage. V is applied to the central electrodes denoted p6 and n6 in each plane. D / 2 and -V D / 2, applying V to the outermost electrodes denoted as p1 and p11 fp Similarly, V is applied to the outermost electrodes n1 and n11. fn The voltages of other segments p2, p3, p4, p5, p7, p8, p9, and p10 can be divided by capacitors (e.g. Figure 3A By changing the voltage ratio V fp / V D and V fn / V D To adjust the focus strength, that is, the value of R2 / R1. According to the PSU voltage V D / 2 and -V D / 2, V fp and V fn ,exist Figure 3A The required voltages are defined in , but we should note that these are exemplary values ​​that apply only to a specific geometry. In general, this approach can be applied to any number of electrode segments. Figure 3A The values ​​provided take into account the capacitor C b (DC blocking capacitors) and the capacitance between adjacent electrodes inform the values ​​of C1 to C5 and C6 to C10. An engineer of ordinary skill can determine the required capacitor values ​​C1 to C5 and C6 to C10. For clarity, the voltage V D / 2 and -V D / 2, V fp and V fn is the asymmetric RF voltage as described above. C b Allows both DC and RF voltages to be applied to each electrode. The DC voltage should be applied to the electrode segments in the same relative ratio as the RF voltage. Note that V D is the total scattered voltage applied across the analysis gap, in this case +V applied to the upward plane D / 2 voltage, and apply -V to the lower plane D / 2 voltage, thus providing V on both sides of the analysis gap D The total voltage. We note that V fp ≠-V fn , V fp ≥+V D / 2, and is always positive, V fn ≥-V D / 2, and can be positive or negative. When focusing is not required, R2 / R1=1, and V fp is set to +V D / 2, and V fp Set to -V D / 2.

[0228] In this example, the transparent mode involves a quadrupole field provided by an AC voltage VT with a typical d=0.5 for confining ions to the FAIMS cell axis. Figure 3B and Figure 3C Two typical electronic schemes for loading a VT (with AC electrodes carrying opposite phases) are shown in FIG. Figure 3B An essentially quadrupole field (used in transmission mode) is shown capable of confining ions without the need for a DC voltage. Figure 3C A linear multipole field is shown (used in transmission mode) which configures the ions along a direction extending between the planes of the segmented electrodes, but an additional DC voltage is required to confine the ions in a lateral direction.

[0229] The PSU that outputs V and VT and their negative corresponding voltages preferably uses a digital power supply, so that d<0.5 or d>0.5 is easily achieved. Figure 3A All of the schemes in ∼C preferably employ an isolating switch or relay operated by a digital controller (not shown). The controller is preferably configured to switch the apparatus between planar FAIMS mode (without ion focusing), gradient FAIMS mode (with adjustable focusing strength), and transparent mode. The symmetric RF of the transparent mode may have a typical harmonic distribution (e.g., Figure 4A as shown) and rectangular distribution (e.g. Figure 4B Any RF form will work, but a rectangular distribution is believed to provide better constraints.

[0230] Digital PSUs easily allow the frequency and amplitude of the waveform to be changed. Figure 2B The typical frequency in separation mode for a 1000 kHz spectral analyzer (device size) is 25 to 500 kHz, depending on the mass and mobility of the ions of interest - lower for heavy, less mobile species such as macromolecules (e.g., proteins), and higher for light, small ions. A commonly used frequency is 200 kHz.

[0231] The optimum frequency in transparent mode is preferably higher. For effective confinement of ions, pressures up to at least 40 mbar are required (reference [8] and reference [9]). The associated number γ, which varies from 1, representing perfect confinement, to 0, representing no confinement, depends on the gas pressure and the RF frequency (see reference

[10] ). Physically, the ion relaxation time must be close to or exceed the RF period. Therefore, for a given pressure, confinement can be improved by increasing the frequency. However, increasing the frequency also reduces the depth of the Dehmelt pseudopotential. This depth can be restored by increasing the RF voltage proportionally up to the electrical breakdown limit. The following table lists the benchmark papaverine 1+ ion (reduced mobility K) at ambient gas temperature (300 K). 0 =1.04cm 2 / vs), showing that different frequencies are required to improve limiting (transmittance) in transparent mode:

[0232]

[0233] Table 1: Benchmark papaverine 1+ ions (reduced mobility K) at ambient gas temperature (300 K) 0 =1.04cm 2 / vs) typical situation

[0234] From this table, it can be inferred that the appropriate pressure and frequency required for good transmission of ions in transparent mode, for example, it can be inferred that 30 mbar and 200 kHz result in negligible confinement (γ=0.001 in transparent mode). Changing the frequency at the same pressure up to 3 MHz (as the preferred digital power supply can do) greatly increases γ to 0.20. However, if the pressure is simultaneously reduced to 5 mbar, this will produce nearly perfect confinement (γ=0.90). Alternatively, reducing the pressure to 1 mbar produces reasonable ion confinement (γ=0.50) at the original 0.2 MHz frequency. These teachings help to derive the conditions used for good transmission of ions in the transparent mode of the LP-FAIMS device.

[0235] 2) Regarding the second aspect of the present invention

[0236] The equipotential surfaces and strength of the cylindrical field in the annular gap between two coaxial cylindrical electrodes for arbitrary R1 and R2, where R1 is the outer radius of the inner electrode and R2 is the inner radius of the outer electrode, are well known.

[0237] For example, we can define χ = R2 / R1. The equipotential surface is defined using Cartesian coordinates x and y according to the following formula:

[0238]

[0239] And the strength of the cylindrical electric field is defined by:

[0240]

[0241] Figure 5A (i) to (iv) show cylindrical fields 502, 504, 506, 508 for different values ​​of χ.

[0242] Figure 5B A rectangular region 510 is shown which can be located at any position within the cylindrical field, wherein equipotential contours are defined with reference to Cartesian x, y coordinates. Each equipotential line has a radius of curvature R and a common center 518. Rectangular region 512 is selected to have the same size and shape as the LP segmented FAIMS device, and a selected gap g and a selected width w are within rectangular region 510. The equipotential contours with radius R1 are tangent to the inner surface of the lower electrode plane 514 at their center points. The equipotential contours with radius R2 are tangent to the inner surface of the upper electrode plane 516 at their center points. The E / N ratio across the segmented FAIMS device is (E / N 下 ) / (E / N 上 )=χ.

[0243] Thus, a direct measure of focus is provided and is independent of the gap g. In other words, this shows that a cylindrical field with a selected χ can be established within a rectangular area independently of g and w by setting the voltage applied to the electrodes accordingly.

[0244] For purposes of illustration (but not limitation), Figure 2B (g = 7.5 mm) and the values ​​of R1, R2 are listed in the table below, yielding χ = 1.1 and 1.5. Therefore, it is proved that LP segmented FAIMS can transmit ions within the range of E / N values ​​determined only by χ. The intensity of the focus at the center of the gap can also be defined based on the gradient of the electric field. For the case of a cylindrical field, by 4 / ln(χ) / R2+R1) 2 The gradient of the electric field is given. That is, ions with a selected K(E / N) dependence are focused toward the isofield contours of a selected radius between R1 and R2.

[0245]

[0246] Table 2: Focus intensity as a function of χ

[0247] Fig. 6A Figure ∼B shows another typical planar FAIMS device.

[0248] In this example, the planar FAIMS device includes a first set of segmented electrodes 602-614 and a second set of segmented electrodes 616-628 arranged in parallel planes and a third set of segmented electrodes 630-634 and a fourth set of segmented electrodes 636-640 in two parallel planes orthogonal to the first set.

[0249] Fig. 6A This planar FAIMS device is shown being used to generate a suitable cylindrical electric field. The necessary voltage on each electrode is determined using equation (2). The center of curvature 650 is located on the bisector of the longer group of central electrodes 622 and 608 at a distance R1 from the inner surface of electrode 622. Equipotential contours according to equation (2) are shown in the FAIMS gap, with the potential of the inner electrode being 0 and the potential of the outer electrode being 1. The voltages on the other electrodes are derived from equation (2) for the center coordinates of the inner face, as illustrated by vectors 652, 654, 656 for each electrode. The resulting contours are essentially the same as Figure 5A The contour lines shown in ~B are repeated to obtain the desired χ value.

[0250] For example, Figure 6B As shown, the same planar FAIMS device can be operated in transparent mode using a quadrupole field 660 with origin 664 at the geometric center of the gap. As illustrated by vectors 664 and 666, the equipotential contours shown are again evaluated at the center of the inner face of the electrode (assuming a symmetric waveform of d=0.5).

[0251] Fig. 7A D shows the segmented planar LP-FAIMS with focusing (focusing provided by the cylindrical field) operating in split mode compared to the segmented planar LP-FAIMS without focusing. Fig. 6A ~B's segmented planar FAIMS device. Fig. 6A The ions in the cylindrical field (here labeled 702) of the device form different domains arranged along the equipotential contours 716. These different domains are based on the applied E C / N cross-gap offset, such as with the applied E C / N increased from 718 to 720 to 722. Measured as the applied E C The intensity of ions passing through the FAIMS gap (y-axis) is a function of / N (x-axis). Figure 7C FAIMS spectrum 706. As with a real cylindrical gap, each ion species has a limited E C / N range, so the peak broadens. However, focusing prevents ion loss due to diffusion in the direction parallel to the electric field. For a standard planar gap FAIMS 714 (known in the art), the inhomogeneous electric field only allows one with a defined E C / N species can be balanced at any position in the gap. However, ion packet 712 is scattered due to free diffusion, such as Figure 7B As shown in FIG. 7 , this is more true in the direction parallel to the electric field than in the direction perpendicular to the electric field. The resulting FAIMS spectrum 710 has the following characteristics: Fig.7D Narrower less intense peaks are shown.

[0252] More specifically, if Fig. 8A As shown in (i), the curved ion domain 804 (shown in a plane orthogonal to the direction of the ion beam through the device 808) extends above and below the projection 832 of the narrow exit slit 810 configured along the mid-gap. Fig. 8A In the vertical projection shown in (ii) of FIG. 8 , the focus is on the ion plume entering through the FAIMS device inlet 802 and compressing the ion plume vertically as it moves toward the outlet 830, thereby approaching the steady-state shape controlled by the equipotential contours as described above. A small portion of the ions approaching the gap outlet passes through the slit 810 (whose shape minimizes the gas flow disturbance in 808) to reach the ion transfer stage 812. The pressures on both sides of the slit 810 are preferably close. As the applied E is scanned (in the direction of increasing or decreasing), the pressure of the ion plume increases. C / N, the curved ion domain moves across the linear gap, and the ions pass through the slit 810 within a limited CV range. This broadens the FAIMS peak and reduces its intensity, such as Fig. 8A As shown in (iii), this is not ideal.

[0253] like Figure 8B As shown in (i) of FIG. 1 , a piecewise planar LP-FAIMS stage 820 with a near-linear field at the center (as established above) focuses the ions into a linear domain 818 configured along the gap span. This means that a shorter vertical steady-state plume can be generated in a narrower E C / N range or even within a single E C / N through the exit slit 826, such as Figure 8B This produces a narrower, more intense peak 816 in the FAIMS spectrum, as shown in (ii). Figure 8B as shown in (iii).

[0254] 3) Regarding the third aspect of the present invention

[0255] Figures 9A to 9B A piecewise planar FAIMS device is shown in which all segments of each electrode carry the same potential (positive potential on one electrode and negative potential on another electrode). Fig.9A and Fig. 9BThe resulting equipotential contours and field intensity contours obtained by numerically solving the Laplace equation using the finite difference method are plotted in Figure 1 , respectively. The absence of field contours near the mid-gap indicates the absence of field gradients, i.e. the electric field is uniform across the gap. Contours near the segment edges show slight gradients in regions of sparse ion density and therefore have no substantial effect on the FAIMS separation. This pattern therefore simulates a standard planar gap FAIMS setup of the prior art.

[0256] The fields solved numerically are described in detail. Fig. 10A As shown in (for example, Figure 5B The isofield contours of a segment of the ideal cylindrical field in the annular gap between unterminated full cylindrical electrodes (as depicted in Fig. 1 ). Terminating these cylindrical electrodes (with open gaps on both sides) with w = 4g makes the contours near the center of the gap essentially planar and parallel, as shown in Fig. Fig. 10B A planar FAIMS stage with an open gap having the same w / g ratio and seven segments in each electrode carrying the appropriate voltage (calculated above) is characterized by a wide range of equal R2 / R1 values ​​(e.g., Fig. 10C As shown, R2 / R1=1.15 and Fig. 10D Similar plane-parallel field contours are shown for R2 / R1=1.6) near the center of the gap.

[0257] There are other methods for providing substantially planar parallel field contours within a limited region of a FAIMS gap, and the above example is not intended to be limiting thereto. This aspect of the invention can produce an E / N gradient substantially similar to that produced by differential electrode heating in a planar FAIMS device, but with the advantages described above. An exit slit that limits the path of ions that can leave the gap and be detected by an MS or other downstream stage causes curved, but non-parallel, field contours to be away from the substantially insubstantial center of the gap.

[0258] The operating pressure can be reduced to a few mbar, and experimental data of 6.2 mbar are given in Section 8. Even at extreme E up to 543 Td D At 1.5 Å / N, the signals for proteins ranging from small to large are large, especially in the less charged states. This ultra-low pressure regime (lower than we or other FAIMS practitioners have expected so far) may provide unique advantages for the separation and study of macromolecular conformations.

[0259] Supporting / Comparative Data

[0260] Fig.11AFigure 4-D shows the simulation of a segmented planar LP-FAIMS device operating in transparent mode. These modes are performed using SIMION software in statistical diffusion simulation (SDS) mode. Protonated papaverine (1+) ions of 340Da mass with experimental K(E / N) dependence are simulated. At 33mbar pressure and 43°C temperature, the buffer gas is N, with an axial flow rate of 10m / s and a transverse velocity of zero. The unit has g=7.5mm, w=30mm (because w / g=4) and a length (L) of 100mm, resulting in a filtration time of 10ms. The frequency of the symmetrical rectangular waveform is 200kHz. The SDS model assumes a steady-state migration condition corresponding to high pressure and low RF frequency (i.e., ions drift at a terminal velocity controlled by the transient field). Then γ is close to zero, and ion confinement is poor, but the ion loss of the FAIMS electrode is still limited in this simulation.

[0261] Fig.11A The example shown has a peak RF amplitude of 50V. Figure 3C 31 segmented electrodes with applied voltage. Isoelectric field contours are plotted at 50 V / cm intervals. Trajectories are shown as infinitely continuous. Thus, the plane shows the maximum lateral extent of 1000 ions during a simulation period of 10 ms. The initial position of the ions is close to the axis.

[0262] exist Fig. 11B In the process, the RF voltage is Figure 3C A dc voltage is applied, and additionally supplemented, to provide a gradient that pushes the ions towards the central axis of the device: the ions are confined in the y-direction by the RF field and in the x-direction by the dc field. Fig. 11C Results with a 7-segment electrode under otherwise identical conditions are shown.

[0263] With a peak amplitude of 200V, Figure 3B An embodiment of a quadrupole field provided by an applied voltage is Fig.11D The ion trajectories were recorded as described above. The ion losses to the electrodes over the simulation time were 7%, even with the constraints of these simulations as described above. The quadrupole field confines the ions better, but requires higher voltages for the same mass range. This superior confinement toward the central axis can alternatively be achieved by reducing the pressure and increasing the frequency as described above (simulations not shown).

[0264] Assume the frequency of the asymmetric waveform is 200kHz, d = 0.2 and other conditions are as follows: Fig.11A ~D, we press Fig. 10C (R2 / R1=1.15) The FAIMS separation mode with a linear field gradient was further simulated. All ions passing through the gap exit face were counted, i.e., the exit aperture (slit) was not considered. Fig.12E shown C / N and E D The resulting CV(DV) curve for the E / N term essentially matches the curve obtained for the standard planar gap FAIMS. C The width and intensity of the E / N peak D The higher the / N, the larger it is.

[0265] Typical measurements were made with a planar LP-FAIMS setup with a slightly smaller g (5 mm), w = 20 mm (because w / g = 4) and L = 100 mm, and also without an exit slit. Ion focusing was achieved by applying a thermal gradient between the electrodes, thereby providing a linear field gradient, and this simulates this aspect of the invention. The filtration time was set relatively long at 50 ms.

[0266] like Fig.13 As shown, the complete E D 1. The resolution / sensitivity graph (showing resolving power versus signal) was measured over a 1.250 MHz / N range, with curve 131 at R2 / R1=1 (no focusing), 133 at R2 / R1=1.03 (very weak focusing), and 135 at R2 / R1=1.07 (weak focusing). Compared to weak focusing (at R=19), very weak and extra weak focusing significantly improve the signal by up to 10 times over the no-focus baseline at the same resolution across the entire R range. Very weak and extra weak focusing can also improve the resolution, for example, from R=19 to a maximum of R=43 at the same sensitivity without focusing at the same signal level.

[0267] This example clearly demonstrates the major advantage of flexible ion focusing in LP-FAIMS in a manner that substantially and qualitatively supersedes prior art understanding in either experiment or theory. That is, focusing (via physical gap curvature or physical gap curvature + temperature gradient) is widely observed to increase the transmittance of all species through the FAIMS gap at the expense of resolution and thus the measured signal (e.g., reference

[11] ) according to reported first principle calculations and numerical simulations. In other words, ion focusing is understood and expected to shift FAIMS performance within the space depicted by the resolution / sensitivity curve of the unfocused case, thereby trading resolution for sensitivity. Fig.13 The sensitivity gain at equal resolution or resolution gain at equal sensitivity or both shown in the present demonstrations are fundamentally beyond the state of the art. Adding an exit slit will provide further gain to any prior art resolution / sensitivity balance.

[0268] Further experiments explored the lower limit of the useful FAIMS pressure range using a planar LP-FAIMS setup with g = 7.5 mm, w = 30 mm, and L = 126 mm driven by a waveform with a frequency of 50 kHz and d = 0.2. In particular, Fig.14A Figure 14B shows data for a representative protein obtained with a low 10 ms filtration time at a pressure of 6.2 mbar. A typical 2D palette 141 of protonated bovine ubiquitin (8.6 kDa) in the 6+ charge state (horizontal axis 143 is E C / N, vertical axis 145 is E D / N) shows a significant signal with an excellent s / n ratio until the horizontal axis 149 is E C / N, vertical axis 148 is the E seen in the EC / N spectrum 147 of the ion signal D The electrical breakdown limit is when E / N=543Td. FAIMS analysis in this E / N range is unprecedented, and there is no known analysis above 300Td in the prior art.

[0269] This previously unattainable state allows the investigation and exploitation of many new phenomena and separations. For example, two different E C (E D ) curves (which may reveal different conformations or protonation schemes of isomers-prototypes) are evident in Figure 14. The resolution is as high as 30, which exceeds that of the D / N, and is competitive for proteins that often include multiple unresolved conformers. For larger proteins and other macromolecules, useful operation should be extended to allow higher E / N, lower pressures down to P ~ 1 mbar, and E / N greater than 1000 Td.

[0270] Possible modifications and applications

[0271] The segmented LP-FAIMS electrodes may be slightly curved.The voltage applied to the slightly curved electrodes may be used to weaken or strengthen the ion focusing provided by the voltage gradient according to the invention.

[0272] The present invention is preferably used in a transparent mode in LP-FAIMS, in which the user does not need to physically remove the device from the mass spectrometer which would normally reduce transmittance. This would make the use of LP-FAIMS more attractive to users, who would be less concerned about problems that might arise due to reduced mass spectrometry sensitivity.

[0273] The features disclosed in the preceding description or the following claims or drawings, expressed in a specific form or in the form of means for performing the disclosed functions or methods or processes for obtaining the disclosed results, may, where appropriate, be used alone or in any combination of these features to realize the invention in various forms.

[0274] Although the present invention has been described in conjunction with the above exemplary embodiments, many equivalent modifications and variations will be apparent to those skilled in the art when the present invention is given. Therefore, the exemplary embodiments of the present invention set forth above are considered to be illustrative rather than restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the present invention.

[0275] For the avoidance of any doubt, any theoretical explanations provided herein are provided to enhance the reader's understanding. The inventors do not wish to be bound by any of these theoretical explanations.

[0276] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0277] Throughout this specification, including the following claims, unless the context requires otherwise, the words "comprise" and "comprising" and variations such as "including", "comprising" and "comprising", will be understood to mean the inclusion of stated integers or steps or groups of integers or steps but not the exclusion of any other integers or steps or groups of integers or steps.

[0278] It must be noted that, as used in this specification and the appended claims, the singular forms "it," "the," and "said" include plural references unless the context clearly indicates otherwise. Ranges may be expressed herein as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when a value is expressed as an approximation by using the antecedent "about," it should be understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and, for example, means + / - 10%.

[0279] References

[0280] Many publications are cited above to more fully describe and disclose the present invention and the prior art to which the present invention relates. The full citations of these references are provided below. Each of these references is incorporated herein in its entirety.

[0281] [1] US8610054B2 (Shimadzu)

[0282] [2] US7863562B2 (Shimadzu)

[0283] [3]RWPurves,et al.,Rev.Sci.Instrum.1998,69,4094

[0284] [4]IABuryakov,et al.,Int.J.Mass Spectrom.Ion Processes 1993,128,143

[0285] [5]http: / / www.faims.com / howpart1.htm

[0286] [6]AAShvartsburg et al.,J.Am.Soc.Mass Spectrom.2013,24,109

[0287] [7]AAShvartsburg et al.,Anal.Chem.2018,90,936

[0288] [8] US 6,107,628

[0289] [9]Y.Ibrahim et al.,J.Am.Soc.Mass Spectrom.2006,17,1299

[0290]

[10] AVTolmachev, Nucl.Instrum.Methods Phys.Res.B 1997,124,112; Y.Ibrahim et al.,ibid

[0291]

[11] AAShvartsburg et al.,Anal.Chem.2006,78,3706

[0292]

[12] US7045778B2

[0293]

[13] US7550717B2

[0294] The following statements forming part of the specification provide a general statement of the disclosure herein:

[0295] A1. An apparatus for performing field asymmetric waveform ion mobility spectrometry, i.e., "FAIMS", comprising:

[0296] a first segmented planar electrode comprising three or more segments, wherein the segments of the first segmented planar electrode are arranged in a first plane and extend in a direction parallel to an analysis axis of the device;

[0297] a second segmented planar electrode comprising three or more segments, wherein the segments of the second segmented planar electrode are arranged in a second plane and extend in a direction parallel to an analysis axis of the device, wherein the first segmented planar electrode and the second segmented planar electrode are separated from each other to provide an analysis gap therebetween;

[0298] a propulsion member for propulsing ions through the analysis gap in a direction parallel to an analysis axis of the device; and

[0299] power supply,

[0300] The device is configured to operate in the following modes:

[0301] a FAIMS mode, wherein the power supply applies a first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component; and

[0302] A transparent mode wherein the power supply applies a second set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate a confining electric field in the analysis gap for focusing ions toward the longitudinal axis.

[0303] A2. The apparatus of statement A1, wherein the gas controller is configured to provide a gas pressure in the analysis gap such that the gas pressure in the analysis gap is lower in the transparency mode than in the FAIMS mode.

[0304] A3. The apparatus of statement A1 or A2, wherein the gas controller is configured to provide a gas pressure of 1 to 200 mbar in the analysis gap in the FAIMS mode.

[0305] A4. An apparatus according to any of the preceding statements, wherein the gas controller is configured to control the gas supply to the analysis gap so that the analysis gap contains a gas mixture, wherein the gas mixture includes two or more of N2, H, and He.

[0306] A5. An apparatus according to any of the preceding statements, wherein the pressure controller is configured to provide a gas pressure of 20 mbar or less in the analysis gap in the transparent mode.

[0307] A6. An apparatus according to any of the preceding statements, wherein the first set of voltage waveforms repeats at a first frequency and the second set of voltage waveforms repeats at a second frequency, wherein the first frequency is lower than the second frequency.

[0308] A7. An apparatus according to any of the preceding statements, wherein the first frequency is in the range of 5 kHz to 5 MHz, and the second frequency is 500 kHz or higher.

[0309] A8. An apparatus according to any of the preceding statements, wherein the first set of voltage waveforms and the second set of voltage waveforms are substantially rectangular.

[0310] A9. An apparatus according to any of the preceding statements, wherein the power supply is a digital power supply.

[0311] A10. An apparatus according to any of the preceding statements, wherein the apparatus is configured to operate at a duty cycle less than or greater than 0.5 in the FAIMS mode.

[0312] A11. An apparatus according to any of the preceding statements, wherein the power supply is configured to apply the first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode by generating one or more RF voltage waveforms and applying the RF voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode via an arrangement of capacitive voltage dividers.

[0313] A12. An apparatus according to any of the preceding statements, wherein the power supply is configured to change the frequency of the voltage waveform applied to the segments of the first segmented planar electrode and the second segmented planar electrode from a first frequency value to a second frequency value substantially instantaneously.

[0314] A13. An apparatus according to any of the preceding statements, wherein the power supply is configured to change the f-value of the voltage waveform applied to the segments of the first segmented planar electrode and the second segmented planar electrode from a first f-value to a second f-value substantially instantaneously.

[0315] A14. An apparatus according to any of the preceding statements, wherein the second set of voltage waveforms has a duty cycle of 0.5.

[0316] A15. An apparatus according to any of the preceding statements, wherein w≥3g, where w is the width of the analysis gap in the gap width direction, and g is the height of the analysis gap in the gap height direction.

[0317] A16. An apparatus according to any of the preceding statements, further comprising the features of any of statements B1 to B16 and / or statements C1 to 11.

[0318] B1. A device for performing field asymmetric waveform ion mobility spectrometry, i.e., "FAIMS", comprising:

[0319] a first segmented planar electrode comprising three or more segments, wherein the segments of the first segmented planar electrode are arranged in a first plane and extend in a direction parallel to an analysis axis of the device;

[0320] a second segmented planar electrode comprising three or more segments, wherein the segments of the second segmented planar electrode are arranged in a second plane and extend in a direction parallel to an analysis axis of the device, wherein the first segmented planar electrode and the second segmented planar electrode are separated from each other to provide an analysis gap therebetween;

[0321] a propulsion member for propulsing ions through the analysis gap in a direction parallel to an analysis axis of the device; and

[0322] power supply,

[0323] wherein the apparatus is configured to operate in a FAIMS mode, wherein in the FAIMS mode the power supply applies a set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component;

[0324] wherein the set of voltage waveforms is configured so that the asymmetric time-dependent electric field has contour lines of equal field strength of a curve when viewed in a plane perpendicular to the analysis axis, so that ions with different differential mobilities are focused toward different spatial domains, wherein each spatial domain extends along a contour line of equal field strength of a corresponding curve when viewed in a plane perpendicular to the analysis axis; and

[0325] The device has a focus controller configured to allow a user to change the curvature of contour lines of equal field strength to change the focusing intensity provided by the asymmetric time-dependent electric field.

[0326] B2. An apparatus according to statement B1, wherein the contour lines of equal field strength of the curve correspond to the electric field generated in the space between two coaxial cylindrical electrodes, wherein the outer radius of the inner cylindrical electrode is R1 and the inner radius of the outer cylindrical electrode is R2.

[0327] B3. An apparatus according to statement B1 or B2, wherein the focus controller is configured to allow a user to change the R2 / R1 ratio of the cylindrical electric field in the analysis gap of the FAIMS apparatus.

[0328] B4. An apparatus according to any of the preceding statements, wherein the first segmented planar electrode and the second segmented planar electrode are arranged on opposite sides of the analysis gap.

[0329] B5. An apparatus according to any of the preceding statements, wherein the apparatus further comprises:

[0330] a third segmented planar electrode comprising two or more segments, wherein the segments of the third segmented planar electrode are arranged in a third plane and extend in a direction parallel to an analysis axis of the device; and

[0331] a fourth segmented planar electrode comprising two or more segments, wherein the segments of the fourth segmented planar electrode are arranged in a fourth plane and extend in a direction parallel to the analysis axis of the device,

[0332] wherein the first segmented planar electrode and the second segmented planar electrode are arranged on opposite sides of the analysis gap and are separated from each other in a gap width direction perpendicular to the analysis axis; and

[0333] Wherein, the third segmented planar electrode and the fourth segmented planar electrode are arranged at opposite sides of the analysis gap and are separated from each other in a gap height direction perpendicular to the analysis axis and the gap width direction.

[0334] B6. The apparatus of statement B5, wherein w<about 8 g.

[0335] B7. An apparatus according to any of the preceding statements, wherein the gas controller is configured to provide a gas pressure of 1 to 200 mbar in the analysis gap in the FAIMS mode.

[0336] B8. An apparatus according to any of the preceding statements, wherein the apparatus comprises a barrier having an exit slit, wherein the barrier is located on the analysis axis so that the propulsion component propels ions toward the barrier, wherein the barrier is configured to prevent ions from reaching a detector of the apparatus unless the ions pass through the exit slit.

[0337] B9. The device of statement B8, wherein the barrier is configured to be removed.

[0338] B10. An apparatus according to statement B8 or B9, wherein the apparatus is configured to allow adjustment of the width of the exit slit provided by the barrier.

[0339] B11. An apparatus according to any one of statements B8 to B10, wherein the apparatus is configured to allow adjustment of the curvature of the exit slit provided by the barrier.

[0340] B12. An apparatus according to any one of statements B8 to B11, wherein the exit slit has a curvature corresponding to the curvature of contours of equal field strength of the asymmetric time-dependent electric field, which are curved in a plane perpendicular to the analysis axis.

[0341] B13. An apparatus according to any of the preceding statements, wherein the apparatus is configured to operate in the following modes:

[0342] a FAIMS mode, wherein the power supply applies a first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component; and

[0343] A transparent mode wherein the power supply applies a second set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate a confining electric field in the analysis gap for focusing ions toward the longitudinal axis.

[0344] B14. An apparatus according to any of the preceding statements, wherein the power supply is configured to apply a set of additional DC voltages, referred to as compensation voltages or "CV", to all segments simultaneously with the first set of voltage waveforms and the second set of voltage waveforms.

[0345] B15. The apparatus of statement B14, wherein the CV has a predetermined value configured to cause ions having a predetermined differential mobility to exit through the exit slit.

[0346] B16. An apparatus according to statement B14 or B15, wherein the apparatus is configured to scan the CV so that ions with different predetermined differential mobilities exit through the exit slit at different times.

[0347] B17. An apparatus according to any of the preceding statements, further comprising the features of any of statements A1 to A15 and / or statements C1 to 11.

[0348] C1. A device for performing field asymmetric waveform ion mobility spectrometry, i.e., FAIMS, comprising:

[0349] a first segmented planar electrode comprising three or more segments, wherein the segments of the first segmented planar electrode are arranged in a first plane and extend in a direction parallel to an analysis axis of the device;

[0350] a second segmented planar electrode comprising three or more segments, wherein the segments of the second segmented planar electrode are arranged in a second plane and extend in a direction parallel to an analysis axis of the device, wherein the first segmented planar electrode and the second segmented planar electrode are separated from each other to provide an analysis gap therebetween;

[0351] a propulsion member for propulsing ions through the analysis gap in a direction parallel to an analysis axis of the device; and

[0352] power supply,

[0353] wherein the apparatus is configured to operate in a FAIMS mode, wherein in the FAIMS mode the power supply applies a first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component; and

[0354] In which, the first set of voltage waveforms is configured so that the asymmetric time-correlated electric field has essentially linear contour lines of equal field strength when viewed in a plane perpendicular to the analysis axis, so as to focus ions with different differential mobilities toward different spatial domains, wherein each spatial domain extends along a corresponding linear contour line of equal field strength when viewed in a plane perpendicular to the analysis axis.

[0355] C2. An apparatus according to statement C1, wherein the apparatus has a focus controller configured to allow a user to change the gradient of contour lines of equal field strength to change the focusing intensity provided by the asymmetric time-dependent electric field.

[0356] C3. An apparatus according to any of the preceding statements, wherein the apparatus comprises a barrier having an exit slit, wherein the barrier is located on the analysis axis so that the propulsion component propels ions toward the barrier, wherein the barrier is configured to prevent ions from leaving the analysis gap unless the ions pass through the exit slit.

[0357] C4. The device of statement C3, wherein the barrier is configured to be removed.

[0358] C5. An apparatus according to statement C3 or C4, wherein the apparatus is configured to allow adjustment of the width of the exit slit provided by the barrier.

[0359] C6. An apparatus according to any one of statements C3 to C5, wherein the exit slit is linear and extends in a direction corresponding to contours of equal field strength of the asymmetric time-dependent electric field viewed linearly in a plane perpendicular to the analysis axis.

[0360] C7. An apparatus according to any of the preceding statements, wherein substantially straight contour lines of equal field strength are substantially straight over a distance of w / 4 or greater, wherein w is the width of the analysis gap in the gap width direction.

[0361] C8. An apparatus according to any of the preceding statements, wherein the power supply is configured to apply a set of additional DC voltages, referred to as compensation voltages or CVs, to all segments simultaneously with the first and second sets of voltage waveforms.

[0362] C9. An apparatus according to statement C8, wherein the CV has a predetermined value configured to cause ions with a predetermined differential mobility to exit through the exit slit.

[0363] C10. An apparatus according to statement C8 or C9, wherein the apparatus is configured to scan the CV so that ions with different predetermined differential mobilities exit through the exit slit at different times.

[0364] C11. An apparatus according to any of the preceding statements, wherein the apparatus is configured to operate in the following modes: a FAIMS mode, wherein the power supply applies a first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-correlated electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component; and a transparent mode, wherein the power supply applies a second set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate a confined electric field in the analysis gap for focusing the ions toward the longitudinal axis.

[0365] C12. An apparatus according to any of the preceding statements, comprising the features of any of statements A1 to A15 and B1 to B16.

Claims

1. A device for performing field asymmetric waveform ion mobility spectrometry (FAIMS), the device comprising: a first segmented planar electrode comprising three or more segments, wherein the segments of the first segmented planar electrode are arranged in a first plane and extend in a direction parallel to an analysis axis of the device; a second segmented planar electrode comprising three or more segments, wherein the segments of the second segmented planar electrode are arranged in a second plane and extend in a direction parallel to an analysis axis of the device, wherein the first segmented planar electrode and the second segmented planar electrode are separated from each other to provide an analysis gap therebetween; a propulsion member for propulsing ions through the analysis gap in a direction parallel to an analysis axis of the device; and power supply, The device is configured to operate in the following modes: a FAIMS mode, wherein the power supply applies a first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate an asymmetric time-dependent electric field in the analysis gap for FAIMS analysis of ions propelled through the analysis gap by the propulsion component; and A transparent mode wherein the power supply applies a second set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode to generate a confining electric field in the analysis gap for focusing ions toward the longitudinal axis using only the second set of voltage waveforms. 2 . The apparatus according to claim 1 , further comprising a gas controller configured to provide a gas pressure in the analysis gap such that the gas pressure in the analysis gap is lower in the transparency mode than in the FAIMS mode.

3. The device according to claim 2, wherein: The gas controller is configured to provide a gas pressure of 1-200 mbar in the analysis gap in the FAIMS mode.

4. The device according to claim 2 or 3, wherein: The gas controller is configured to control the gas supply to the analysis gap such that the analysis gap contains a gas mixture, wherein the gas mixture includes two or more of N 2 , H, and He.

5. The device according to claim 2 or 3, wherein: The gas controller is configured to provide a gas pressure of 20 mbar or less in the analysis gap in the transparent mode.

6. The device according to any one of claims 1 to 3, wherein: The first set of voltage waveforms repeats at a first frequency, and the second set of voltage waveforms repeats at a second frequency, wherein the first frequency is lower than the second frequency.

7. The device according to claim 6, wherein: The first frequency is in the range of 5 kHz to 5 MHz, and the second frequency is 500 kHz or higher.

8. The device according to any one of claims 1 to 3, wherein: The first set of voltage waveforms and the second set of voltage waveforms are substantially rectangular.

9. The device according to any one of claims 1 to 3, wherein: The power supply is a digital power supply.

10. The device according to claim 2 or 3, wherein: The apparatus is configured to operate in the FAIMS mode at a duty cycle less than or greater than 0.

5.

11. The device according to any one of claims 1 to 3, wherein: The power supply is configured to apply the first set of voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode by generating one or more RF voltage waveforms and applying the RF voltage waveforms to segments of the first segmented planar electrode and the second segmented planar electrode via an arrangement of capacitive voltage dividers.

12. The device according to any one of claims 1 to 3, wherein: The power supply is configured to substantially instantaneously change a frequency of a voltage waveform applied to segments of the first segmented planar electrode and the second segmented planar electrode from a first frequency value to a second frequency value.

13. The device according to any one of claims 1 to 3, wherein: The power supply is configured to substantially instantaneously change an f-value of a voltage waveform applied to segments of the first segmented planar electrode and the second segmented planar electrode from a first f-value to a second f-value.

14. The device according to any one of claims 1 to 3, wherein: The second set of voltage waveforms has a duty cycle of 0.

5.

15. The device according to any one of claims 1 to 3, wherein: w≥3g, where w is the width of the analysis gap in the gap width direction, and g is the height of the analysis gap in the gap height direction.

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