Differential ion mobility analysis

Abstract

A method for analyzing ions includes generating ions from a sample in an ion source and delivering the ions into a vacuum region of a vacuum enclosure containing an ion mobility analyzer having an ion drift region formed between opposing electrodes defining an analytical gap. The ions emerge from an ion inlet as a supersonic jet of buffer gas in which the ions are transported. A differential ion mobility analysis is then performed on the ions in an initial vacuum region, prior to mass spectrometry analysis of the ions in a downstream vacuum region, for example. Prior to performing the differential mobility analysis (and, for example, mass spectrometry analysis) of the ions, the method includes: a) varying the flow rate of gas entering or exiting the vacuum region; b) measuring the gas pressure within the vacuum region; repeating steps a) and b) until a target gas pressure value is achieved; c) measuring the velocity of the gas flow along the drift region; and repeating steps a) through c) until the measured gas velocity value reaches a predetermined target gas velocity value. The differential mobility analysis and mass spectrometry analysis are then performed based on the target gas pressure value and the target gas velocity value.

Description

[Technical Field]

[0001] The present invention relates to ion mobility spectrometry (IMS), particularly but not exclusively to field asymmetric IMS (FAIMS) and differential mobility spectrometry (DMS). [Background technology]

[0002] The term ion mobility spectrometry (IMS) refers to methods and apparatus used to characterize a population of ions originating from a sample material in terms of the forward velocity of the ions as they are propelled by an applied electric field through a supporting gas atmosphere. Ion mobility measurements involve injecting the ion population into a "drift region," often using an ion shutter at the entrance to the drift region to control the timing of the injection process. An ion detector, or simply an ion outlet, may be located at the output end of the drift region. While in the drift region, the ion population moves longitudinally toward the exit end of the drift region, carried in a flow of purified, neutral supporting gas (e.g., molecular nitrogen), also known as a "buffer gas." Simultaneously, the ion population moves transversely to the buffer gas flow direction under the driving force of an applied electric field E, generated by an appropriate voltage gradient applied transversely to the buffer gas flow direction.

[0003] It is worth noting that ion mobility measurements relate only to ion populations, not to individual ions, whose velocities can be relatively large. For example, the median inter-collision velocity of nitrogen molecular ions at atmospheric pressure and a temperature of 25°C is about 450 meters per second. In contrast, for example, an ion population may move transverse to the direction of buffer gas flow, typically propelled by an applied electric field E, at a velocity of, say, v = 4 m / s.

[0004] It is customary to normalize the velocity value v of such an ion population by dividing it by the value of the electric field strength E applied transverse to the buffer gas flow direction. This normalization yields the ion mobility coefficient K = v / E, which is a measure of the ion population velocity per unit electric field strength. The relationship between ion population velocity v and electric field strength E is valid for an ion population at a thermal energy measured in a buffer gas atmosphere of constant composition, pressure, and temperature. Importantly, the value of the ion mobility coefficient depends on the temperature T and pressure P of the buffer gas in the drift region. Consequently, the ion mobility coefficient K is sensitive to variations in both of these quantities.

[0005] One difference between IMS and mass spectrometry (MS) is that ions are characterized in a continuously replenished supporting buffer gas atmosphere (also called drift gas), whose primary practical purpose is to maintain a purified and constant atmosphere for the collision-based motion of ion populations.

[0006] Electric field asymmetric IMS, differential mobility spectrometry, or ion drift spectrometry are different names given to the same process, which is a type of IMS. Ion mobility measurements begin when ions formed from components in the sample, called product ions, are injected into the drift region. These methods are based on the fact that when the particle number density N of the buffer gas, i.e., the number of buffer gas particles per unit volume, is constant, a change in the applied transverse electric field E will change the ion mobility coefficient K of the ions. Specifically,

number

number

[0007] Each term α 2n(n=1, 2, ...) are constant coefficients with values ​​specific to a given combination of ion and buffer gas settings. The function α(E / N) expresses the dependence of ion mobility on the ratio E / N of the electric field strength to the neutral gas density. The unit of E / N is Townsend (Td), where 1Td=10 -17 Vcm 2 This function describes the nonlinear dependence of the ion mobility on the electric field. One IMS technique approach allows the study of the electric field dependence using field asymmetric ion mobility spectrometers (FAIMS) or DMS. The high field asymmetric IMS method for ion separation is based on the highly nonlinear dependence of the ion mobility coefficient on the electric field.

[0008] In this method, variously called Field Asymmetric IMS (FAIMS) or Differential Mobility Spectroscopy (DMS), ions are carried by a gas flow through a drift space between conductive surfaces (e.g., electrodes). The space between the electrodes defines an "analytical gap." The drift space can be defined between curved or flat parallel electrodes (e.g., plates). A "dispersion voltage" (V D A transverse electric field E is applied across the analytical gap using an asymmetric voltage waveform known as D This means that, for example, in the positive amplitude part of the asymmetric wave cycle, E D = +20000V / cm or more, and E D = -1000V / cm. A population of ions moves with a velocity v in an electric field E according to the following equation:

number

[0009] Of course, E D The value of changes magnitude and polarity as the wave cycle switches between its positive and negative amplitude portions. As a result, K(E D / N) is the value of α(E DFor ions where / N) ≠ 0, the dispersion voltage (V D ) asymmetric voltage waveform is designed so that the integrals of these two parts of the wave cycle are equal. Notably, E D Mobility coefficient K(E D / N) (i.e., even at high electric field values, α(E D Ions for which K = E (for which K = E) pass through the drift region and emerge from it, where they can be detected. D (i.e., α(E D / N)≠0) ions are those in which the ion population is subjected to an electric field E D As the electrons are repeatedly exposed to periodic changes in the direction and intensity of the electric field, they experience a net displacement towards the surface of one of the electrodes. The magnitude of the displacement is determined by the mobility K(E D / N).

[0010] The dispersive electric field E in DMS or FAIMS D The direct effect of the distributed electric field strength E at the extremes of the asymmetric waveform is D Ion mobility K(E D / N). The waveform shows that the mobility is dispersive with the electric field strength E D The electric field strength E is such that ions with little or no dependence on D and the duty cycle (between the duration of each positive and negative polarity portion) is designed. The mobility is determined by the dispersion electric field strength E D Ions, which depend on the dispersive voltage waveform, are continuously displaced from the central ionic axis of the ion stream with each complete cycle of the dispersive voltage waveform. Eventually, the ion population strikes the electrodes defining the analytical gap, loses charge, and is removed from the measurement process. Applying a DC "compensation voltage" to the analyzer electrodes can compensate for the effect of the dispersive electric field, thereby directing the ion motion back toward the center of the analyzer.

[0011] The DC electric field is divided into a dispersed electric field ED A relatively low direct current (DC) "compensation voltage" (V) is superimposed on the electrode to allow the movement of ions towards one of the electrodes to be controlled or "compensated." C ) can be added to the electrodes or plates that define the analytical gap. Ions returned to the center of the analytical gap are allowed to pass through the drift region. Sweeping this compensation voltage, often from 10 to 40 V (creating an electric field of 100 to 500 V / cm), provides a means of measuring the mobility of all ions in the analyzer for a given dispersion voltage waveform. This method allows for ion mobility filtering, with separation of ions based on differences in ion mobility, hence the name "differential mobility analysis" (also known as FAIMS).

[0012] US Patent No. 5,999,623 discloses an apparatus and method for ion analysis using vacuum differential ion mobility spectrometry (DMS) in combination with mass spectrometry. The disclosure teaches utilizing a working pressure for a buffer gas in which ions are transported to perform field asymmetric ion mobility (FAIMS) analysis.

[0013] US Pat. No. 6,299,499 discloses a method and system for a vacuum-driven differential ion mobility spectrometry / mass spectrometry interface with adjustable resolution and selectivity.

[0014] In order to achieve high quality measurements, it is necessary to properly control the velocity of the gas flow in the analytical gap. The present invention has been made in view of the above circumstances. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] US 8610054 B2 [Patent Document 2] US 8084736 B2 [Non-patent literature]

[0016] [Non-Patent Document 1] IA Buryakov, et al., Int. J. Mass Spectrom. Ion Processes 1993, 128, 143 [Non-patent document 2] RW Purves, et al., Rev. Sci. Instrum. 1998, 69, 4094 [Non-patent document 3] GE Spangler and CI Collins, “Peak Shape Analysis and Plate Theory for Plasma Chromatography”, Analytical Chemistry, Vol. 47, No. 3, March 1975 Summary of the Invention [Means for solving the problem]

[0017] Most generally, the present invention proposes a method (and apparatus configured therefor) for analyzing ions by ion mobility spectrometry (IMS) by generating ions from a sample in an ion source, carrying the ions in a buffer gas (preferably the buffer gas is a supersonic jet) and delivering the ions into an ion mobility spectrometer within a vacuum region including an ion drift region formed between electrodes defining an analytical gap. Prior to performing differential ion mobility analysis of the ions, a) varying the flow rate of gas into or out of said vacuum region; b) measuring the gas pressure within the vacuum region; Steps a) and b) are repeated until the measured gas pressure value reaches a predetermined target gas pressure value. c) measuring the velocity of the gas flow along the drift region; repeating steps a) through c) until the measured gas velocity value reaches a predetermined target gas velocity value, and then performing a differential ion mobility analysis of the transported ions based on the target gas pressure value and the target gas velocity value. In this way, a predetermined target gas velocity and a predetermined target gas pressure can be achieved, ready for use in a subsequent differential ion mobility spectrometry (DMS or FAIMS) performed as a standalone ion mobility spectrometry analysis or as an upstream portion of a larger spectrum analysis, for example, to direct ions downstream into a mass analyzer.

[0018] As a result, the velocity of the buffer gas flow (and entrained ion flow) through the drift region can be controlled independently of the value of the gas pressure in the initial vacuum region.

[0019] Preferably, the buffer gas is a supersonic jet. Most desirably, the flow of gas (and entrained ions) through the drift region is driven by a supersonic jet of buffer gas (e.g., the momentum of the gas flow is primarily or almost entirely provided by the jet) rather than by a pressure difference between the gas inlet end and the gas outlet end of the drift region. For example, preferably, the pressure difference between the gas inlet end and the gas outlet end of the drift region may be negligibly small.

[0020] Choke flow

[0021] A supersonic jet of buffer gas has a limit to the maximum mass flow rate of a fluid. This phenomenon begins at the throat of the gas outlet under sonic conditions and continues along the jet, when the downstream fluid can no longer communicate with the upstream flow. This is because the maximum speed at which fluid property information propagates through a flow is the speed of sound. In a jet, the flow is supersonic, meaning the fluid moves faster than the speed of sound. Therefore, the fluid properties at the gas outlet are independent of the downstream fluid properties. Further expansion of the flow in the jet, which increases velocity and reduces pressure, does not further increase the mass flow rate. When this occurs, the flow is said to be "choked," and the mass flow rate is determined by the open area of ​​the gas outlet, regardless of how low the outlet pressure is. Choked flow is a limiting condition where further reductions in the downstream pressure environment for a fixed upstream pressure and temperature no longer increase the mass flow rate. Choked gas flow results in a condition where the mass flow rate is independent of downstream pressure.

[0022] In the present invention, a supersonic jet is generated at the ion source exit (e.g., capillary) where it enters the initial vacuum region. This is created by a significant pressure difference maintained between the ion source (e.g., atmospheric pressure ion source) and the initial vacuum region (significantly below atmospheric pressure) of an ion mobility spectrometry (IMS) instrument (e.g., a low-pressure FAIMS instrument (LP-FAIMS)). Under these conditions, a Mach field is formed at the ion source exit (e.g., capillary), which forms a supersonic gas jet. The exiting gas jet is characterized by a jet pressure ratio (JPR), which typically has a JPR value of >1.5, typically >5, more preferably >10, and even more preferably >15, e.g., a JPR value of about 20 (JPR=20). If JPR>≈1.5, the jet is supersonic.

[0023] The emerging jet is most preferably not very divergent and supersonic, and the gas flow in the jet is most preferably choked, meaning that reducing the downstream pressure in the jet does not increase the velocity or throughput of the gas jet. The present invention provides a process and apparatus for controllably monitoring and adjusting the drift velocity of buffer gas and entrained ions through the drift region of an ion mobility spectrometry (IMS) device under these circumstances.

[0024] Thus, in a first aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: generating ions from a sample in an ion source; delivering the ions through an ion inlet into a vacuum region of a vacuum enclosure comprising a differential ion mobility spectrometer comprising an ion drift region formed between opposing electrodes defining an analytical gap, wherein the ions emerge from the ion inlet and into the drift region as a supersonic jet of buffer gas in which the ions are carried; and delivering the ions from the differential ion mobility spectrometer to an ion detector to generate one or more ion mobility spectrum peaks; An ion analysis method comprising: a) varying the flow rate of gas into or out of said vacuum region; b) measuring the gas pressure within the vacuum region and comparing the measured gas pressure value with a target gas pressure value; repeating steps a) and b) until the gas pressure comparison indicates that the measured gas pressure value has reached the target gas pressure value; c) measuring the velocity of the gas flow along the drift region by applying a gate voltage pulse across the analytical gap to act as an ion shutter, detecting an ion mobility spectrum peak produced by the ion detector, adjusting the pulse width of the gate voltage pulse so that the detected ion mobility spectrum peak reaches a reduced height (H2) that is lower than a maximum detected height (H1) of the ion mobility spectrum peak, the reduced height (H2) being in accordance with a predetermined relative ratio R, such that R=H2 / H1, and determining the velocity of the gas flow as v=L / T based on the ratio v of the pulse width T to the axial length L of the drift region; repeating steps a) to c) until the measured gas velocity value reaches a predetermined target gas velocity value, and then performing a differential ion mobility analysis using the differential ion mobility analyzer based on the target gas pressure value and the target gas velocity value. The present invention provides a method comprising:

[0025] The method may include, after the differential ion mobility analysis by the ion mobility spectrometer, delivering the ions from the vacuum region through an ion outlet into a downstream vacuum region of the vacuum enclosure, and performing mass spectrometric analysis of the ions in that region.

[0026] Preferably, the predetermined relative ratio R has a value between 0.4 and 0.6 (e.g. R=0.5), as values ​​in this range have been found to provide good sensitivity and accuracy in determining the gas flow velocity v=L / T.

[0027] Differential ion mobility analysis is performed by applying a dispersive electric field E across the analytical gap. D is the dispersed electric field E D The method may further comprise generating a dispersed electric field E across the analytical gap based on the amplitude of a dispersed voltage waveform used to generate the dispersed electric field E across the analytical gap. D Generating the dispersion voltage V of an asymmetric waveform (e.g., square / rectangular waveform) DThe method may include generating the dispersive electric field by applying a dispersive voltage waveform V that alternates in polarity among a plurality of adjustable dispersive voltage amplitude values ​​to one or more of the electrodes that define the analytical gap. D The differential ion mobility analysis may include providing a power supply having a switch configured to switch to provide a compensating electric field E across the analytical gap. C Generating a compensation electric field across the analytical gap may include applying a DC compensation voltage V to one or more of the electrodes defining the analytical gap. C The method may include generating the compensating electric field by applying a

[0028] The method preferably includes establishing a flow of gas into said vacuum region to provide a gaseous medium for said differential ion mobility means. In use, said vacuum region containing said differential ion mobility means preferably has a pressure within said vacuum region of between 1 mbar and 100 mbar, or preferably between 10 mbar and 40 mbar, or between 30 mbar and 35 mbar.

[0029] Preferably, the vacuum region includes an upstream vacuum subregion including the ion inlet and another downstream vacuum subregion including the ion outlet, and the method includes communicating gas flow between the upstream vacuum subregion and the downstream vacuum subregion through (e.g., only through) the drift region. Dividing the interior space of the first vacuum region in this manner has the advantage that buffer gas flow from the ion output end of the drift region of the vDMS assembly does not return to the ion input end of the drift region of the vDMS assembly. As a result, pressure control within the vacuum region is simplified. The pressure difference between the pressure in the upstream vacuum subregion and the pressure in the downstream vacuum subregion can be minimized to be substantially eliminated or negligible within the limits of the measurement accuracy of a manometer (e.g., below the accuracy of a diaphragm gauge). As a result, the pressure difference between the gas inlet end and the gas outlet end of the drift region can be minimized to be substantially eliminated or negligible within the limits of the measurement accuracy of a manometer.

[0030] Preferably, varying the flow rate of gas into or out of the vacuum region comprises providing an adjustable gas flow port in the vacuum region separate from the ion inlet and the ion outlet, the adjustable gas flow port being configured to allow an adjustable flow of gas to enter or exit the vacuum region therethrough, and the method comprises adjusting the adjustable gas flow port to vary the flow of gas therethrough.

[0031] Preferably, varying the flow rate of gas into or out of the vacuum region comprises providing each of the upstream vacuum sub-region and the downstream vacuum sub-region with a respective adjustable gas flow port configured to allow an adjustable flow of gas to enter or exit the upstream vacuum sub-region or downstream vacuum sub-region therethrough, and the method comprises adjusting each adjustable gas flow port to vary the flow of gas therethrough.

[0032] In a second aspect, the present invention may provide an ion analysis apparatus comprising an ion source configured to generate ions from a sample, and an ion detector, wherein in use ions travel along an ion optical axis from the ionization source to the ion detector, the apparatus further comprising: A vacuum enclosure containing a differential ion mobility spectrometer including a vacuum region with an ion inlet and an ion outlet, the vacuum region having an ion drift region formed between opposing electrodes defining an analytical gap. Equipped with the ion source is configured to deliver ions through the ion inlet into the vacuum region such that the ions emerge from the ion inlet and enter the drift region as a supersonic jet of buffer gas in which the ions are carried, and in use ions generated from the sample are subjected to differential ion mobility analysis, the differential ion mobility spectrometer being configured thereafter to deliver the ions to the ion detector to produce one or more ion mobility spectral peaks; The ion analyzer is a) varying the flow rate of gas into or out of said vacuum region; b) measuring the gas pressure within the vacuum region and comparing the measured gas pressure value with a target gas pressure value; repeating steps a) and b) until the gas pressure comparison indicates that the measured gas pressure value has reached the target gas pressure value; c) measuring the velocity of gas flow along the drift region by applying a gate voltage pulse across the analytical gap to act as an ion shutter, detecting an ion mobility spectrum peak produced by the ion detector, adjusting a pulse width T of the gate voltage pulse so that the detected ion mobility spectrum peak reaches a reduced height H2 that is lower than a maximum detected height H1 of the ion mobility spectrum peak according to a predetermined relative ratio R, such that R=H2 / H1, and determining the velocity of the gas flow based on a ratio v of the pulse width T to an axial length L of the drift region, as v=L / T; repeating steps a) through c) until the measured gas velocity value reaches a predetermined target gas velocity value. a controller configured to perform the process of The ion analyzer is then configured to perform the differential ion mobility analysis based on the target gas pressure value and the target gas velocity value.

[0033] The vacuum enclosure may include a downstream vacuum region including a mass analyzer, and the ion outlet may be configured to deliver ions from the vacuum region into the downstream vacuum region for mass spectrometric analysis of the ions.

[0034] The device may be configured so that the predetermined relative ratio R has a value between 0.4 and 0.6 (eg R=0.5).

[0035] The apparatus generates a dispersed electric field E across the analytical gap. D is the dispersed electric field E D The dispersive electric field E across the analytical gap may be generated based on the amplitude of a dispersive voltage waveform used to generate the dispersive electric field E across the analytical gap. D Generating the dispersion voltage V of an asymmetric waveform (e.g., square / rectangular waveform) D The apparatus may include generating the dispersive electric field by applying a dispersive voltage waveform V that alternates in polarity among a plurality of adjustable dispersive voltage amplitude values. D The apparatus may comprise a power supply comprising a switch configured to switch to provide a compensating electric field E across the analytical gap. C The apparatus may be configured to perform differential ion mobility analysis by a process including generating a DC compensation voltage V to one or more of the electrodes defining the analytical gap. C The analytical gap may be configured to generate a compensation electric field across the analytical gap by generating the compensation electric field by applying

[0036] Preferably, the vacuum region includes an upstream vacuum subregion including the ion inlet and another downstream vacuum subregion including the ion outlet, and the apparatus is configured to communicate gas flow between the upstream and downstream vacuum subregions via the drift region. As previously mentioned, an advantage of dividing the interior space of the first vacuum region in this manner is that the flow of buffer gas from the ion output end of the drift region of the vDMS assembly does not return to the ion input end of the drift region of the vDMS assembly. This simplifies pressure control within the vacuum region. The apparatus is preferably configured to minimize the pressure difference between the pressure in the upstream vacuum subregion and the pressure in the downstream vacuum subregion to be substantially zero or negligible within the limits of the measurement accuracy of a pressure gauge (e.g., less than the accuracy of a diaphragm gauge). As a result, the apparatus can produce a minimized pressure difference between the gas inlet end and the gas outlet end of the drift region to be substantially zero or negligible within the limits of the measurement accuracy of a pressure gauge.

[0037] The apparatus may include an adjustable gas flow port in the vacuum region separate from the ion inlet and the ion outlet configured to allow an adjustable flow of gas to enter or exit the vacuum region through the adjustable gas flow port, and the controller may be configured to adjust the adjustable gas flow port to vary the flow of gas therethrough and thereby vary the rate of gas flow into or out of the vacuum region.

[0038] The apparatus may be configured such that each of the upstream and downstream vacuum sub-regions includes a respective adjustable gas flow port configured to allow an adjustable flow of gas to enter or exit the upstream or downstream vacuum sub-region therethrough, and the controller is configured to vary the flow rate of gas into or out of the respective upstream or downstream vacuum sub-region, thereby varying the flow rate of gas into or out of the first vacuum region.

[0039] The device may be configured to provide a pressure range within the vacuum region of between 1 mbar and 100 mbar, or preferably between 30 mbar and 35 mbar.

[0040] Combinations of the described aspects and preferred features are encompassed by the present invention unless such combinations are clearly impermissible or explicitly avoided. [Brief explanation of the drawings]

[0041] BRIEF DESCRIPTION OF THE DRAWINGS Embodiments and experiments illustrating the principles of the present invention will now be discussed with reference to the accompanying drawings, in which: FIG.

[0042] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a vacuum differential mobility mass spectrometer. [Figure 2] FIG. 1 is a schematic diagram illustrating an example of a vacuum differential mobility mass spectrometer. [Figure 3a] Schematic diagram of one of four alternative examples of a vacuum differential mobility mass spectrometer. [Figure 3b] Schematic diagram of one of four alternative examples of a vacuum differential mobility mass spectrometer. [Figure 3c] Schematic diagram of one of four alternative examples of a vacuum differential mobility mass spectrometer. [Figure 3d] Schematic diagram of one of four alternative examples of a vacuum differential mobility mass spectrometer. [Figure 4a]10A-10C are schematic diagrams of four further examples of vacuum differential mobility mass spectrometers. [Figure 4b] 10A-10C are schematic diagrams of four further examples of vacuum differential mobility mass spectrometers. [Figure 4c] 10A-10C are schematic diagrams of four further examples of vacuum differential mobility mass spectrometers. [Figure 4d] 10A-10C are schematic diagrams of four further examples of vacuum differential mobility mass spectrometers. [Figure 5a] FIG. 1 is a graphical illustration of an example ion detector signal concurrently with a series of gate voltage pulses applied across the analytical gap in the drift region of a differential mobility spectrometer, which acts as an ion gate to alternately allow or prevent ions from passing. [Figure 5b] FIG. 1 is a graphical illustration of an example ion detector signal concurrently with a series of gate voltage pulses applied across the analytical gap in the drift region of a differential mobility spectrometer, which acts as an ion gate to alternately allow or prevent ions from passing. [Figure 5c] FIG. 10 graphically illustrates various examples of ion detector signals resulting from the application of gate voltage pulses with various gate voltage pulse widths across the analytical gap in the drift region of a differential mobility spectrometer, which acts as an ion gate to allow or prevent ions from passing. [Figure 6] FIG. 1 is a diagram showing a schematic diagram of a method for ion analysis. [Figure 7] Graphical heat maps showing the differential mobility spectral peak intensities (heights) for each sample of ions (a) when subjected to a drift velocity of 25 m / s within the drift region of a differential mobility spectrometer, and (b) when subjected to a drift velocity of 2.6 m / s within the drift region of the differential mobility spectrometer. [Figure 8] Schematic diagram of the components of a low-pressure (LP) FAIMS instrument. DETAILED DESCRIPTION OF THE INVENTION

[0043] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying drawings. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated by reference.

[0044] Ion mobility spectrometry (IMS), including differential mobility spectrometry (DMS) [Non-Patent Document 1] and field asymmetric waveform ion mobility spectrometry (FAIMS) [Non-Patent Document 2], is an established method for separating different ion species based on their differences in mobility in a gas as a function of the applied force on the ions via the strength of the ion electric field. This mobility difference depends on the physical and chemical properties of the ions and gas particles (e.g., neutral particles such as atoms and / or molecules) but is only weakly related to the ion mass. The resulting strong orthogonality of this method to mass spectrometry (MS) makes FAIMS / MS a powerful analytical approach.

[0045] Referring to Figure 1, the basic principles and mechanisms of IMS separation, which is based on the nonlinear dependence of ion mobility on electric field and pressure, are illustrated schematically. Ions are carried in a buffer gas flow 100 that flows along the axis of a drift region defined between two (or more) opposing electrodes 14. A high frequency asymmetric AC waveform 30 is applied to one of the two opposing electrodes. This generates a dispersion voltage V D This is known as the dispersion voltage, which causes the ions to be spatially separated due to differences in ion mobility through the buffer gas in which they are transported. D =-(dV D (x) / dx) causes the motion of ions in the direction of the dispersive electric field extending from one of the two electrodes to the other. Combined with the concurrent drift motion of ions in the direction of the buffer gas flow, the resulting ion path is determined by the dispersion voltage V D The polarity of alternates between positive and negative values, resulting in a dispersed electric field E Dfollows a zigzag pattern as it alternates between opposite directions transverse to the gas drift direction.

[0046] Superimposed on the waveform is a slow compensating DC voltage waveform 40 which comprises a series of "sawtooth" DC ramps. This results in a compensation voltage V C It is known as the dispersion voltage V D The frequency of the asymmetric waveform 30 typically ranges between several hundred KHz and around 1 MHz, whereas the frequency of the "sawtooth" DC ramp 40 typically repeats slower than 1 Hz. The amplitude of the asymmetric waveform of the dispersed electric field when the IMS is operating at atmospheric pressure is limited by the breakdown limits of the gas flowing within a given electrode geometry, and in a parallel plate IMS system the field is typically 3 kV mm -1 does not exceed.

[0047] Still referring to FIG. 1, ion separation is possible using waveforms that are significantly different from purely rectangular waveforms. A family of waveforms based on quasi-sinusoidal variations in voltage as a function of time is widely used. They are bi-sinusoidal, truncated sinusoidal, or other substantially rectangular waveforms. Asymmetric waveforms are designed so that the area of ​​the positive pulse portion of one waveform cycle matches the area of ​​the negative pulse portion, i.e., A1 = A2. Therefore, for this particular configuration of time-dependent electric fields, ions with mobilities independent of changes in electric field and pressure will propagate when the compensation voltage is zero. A waveform is characterized by its duty cycle 50, which is usually the width T of the short positive pulse portion of one waveform cycle. H is defined as the total duration of one wave cycle, which defines the waveform period T (i.e., d=T H The width T of the short positive pulse portion of the waveform cycle is defined as H and the long negative pulse part T L The sum of and is equal to the total duration T of one wave cycle.

[0048] There is an optimum duty cycle for separating certain types of ions. For example, type A and C ions are best resolved in IMS spectra when the duty cycle is d≈0.33. Type B ions exhibit more complex behavior, so the ability to vary the duty cycle during an experiment is essential for improving instrument performance.

[0049] 1 also shows a stable ion trajectory 60 that passes safely through the drift region, and a second ion trajectory that strikes the upper DMS electrode 70. To successfully transport the lost ion 70, an appropriate compensation voltage (V C ) 40 must be applied to the IMS electrodes. C By scanning the drift region, ions with different nonlinear dependences of their mobilities on the electric field and pressure are transported successively through the gap in the drift region and can be detected on a plate connected to an electrometer 90 (not shown) or detected / monitored by a mass analyzer 90 (not shown).

[0050] 2 shows a schematic diagram of a low-pressure FAIMS (LP-FAIMS) apparatus, also referred to herein as a vacuum differential ion mobility spectrometer (vDMS). The low-pressure FAIMS (LP-FAIMS) ion analyzer includes an atmospheric pressure (API) ion source 2 configured to generate ions from a sample. The apparatus further includes a vacuum enclosure including an initial vacuum region 6 containing a differential ion mobility analyzer having an ion drift region formed between opposing electrodes that define an analytical gap g, and a downstream vacuum region 8 containing either an ion detector configured to detect ions from the initial vacuum region and generate one or more ion mobility spectral peaks, or a mass spectrometer including an ion detector and configured to perform mass spectral analysis of ions from the initial vacuum region.

[0051] The API source 2 is configured to generate a stream of ions carried in a buffer gas that flows from the API source 2 along a capillary 4 configured with a capillary exit opening located in an initial vacuum region 6. The apparatus is configured such that the stream of buffer gas in which the ions are carried passes through the apparatus along an ion optical axis of the apparatus from the ionization source to an ion detector located in a downstream vacuum region 8, either alone or within a mass spectrometer. The downstream vacuum region is configured in gas flow communication with the initial vacuum region through an initial vacuum region ion outlet 16 that includes a skimmer (which outlet also defines the downstream vacuum region ion inlet).

[0052] The ion source capillary 4 is configured to deliver ions through the ion inlet into the initial vacuum region 6 such that ions emerge from the ion inlet as a supersonic jet of buffer gas in which the ions are carried. The gas stream thus formed flows into a drift region between electrodes 14 where, in use, ions generated from the sample undergo differential ion mobility analysis. An ion outlet 16 of the initial vacuum region 6 is configured to deliver the ions into the downstream vacuum region 8 for subsequent mobility spectrometry or mass spectrometry analysis.

[0053] The ion analyzer includes a controller (22, 24) configured to execute the following process before performing the above-described differential ion mobility analysis and mobility spectrum detection or mass spectrum analysis of the ions. The process is executed to control the flow rate of the buffer gas, and thus the velocity of the ions carried in the buffer gas, which moves at the same velocity as the buffer gas, so that the velocity reaches a desired value. The pressure of the buffer gas in the analytical gap is also controlled to achieve a desired value by the following process. This process allows the velocity of the buffer gas (and ions) in the analytical gap to be selectively controlled independently of the pressure of the buffer gas in the analytical gap. Specifically, the process includes: a) varying the flow rate (n5, n6) of buffer gas into or out of the initial vacuum region; b) measuring the buffer gas pressure via a pressure sensor 18 located in the drift region of the vDMS assembly within the initial vacuum region 6 and comparing the measured gas pressure value with a target gas pressure value; repeating steps a) and b) until the buffer gas pressure comparison indicates that the measured gas pressure value has reached the target gas pressure value. The process then includes: c) measuring the velocity of the buffer gas flow along the drift region formed between the electrodes 14 of the device; repeating steps a) through c) until the measured buffer gas velocity value reaches a predetermined target gas velocity value.

[0054] Once the target values ​​for the velocity of the buffer gas (and ions) are achieved when the buffer gas is at a pressure equal to the target buffer gas pressure value, the ion analyzer is subsequently configured to perform differential ion mobility analysis and / or mass spectrometry analysis under those target gas pressure and target gas velocity values.

[0055] Step c) of measuring the rate of buffer gas flow is performed by a control device comprising a gas flow control assembly (19, 20), a gas pressure monitoring unit 22, and a processor unit 24 configured to perform the calculations referred to herein based on the values ​​of buffer gas pressure provided by the gas flow control and gas pressure monitoring unit 22 and based on the pulse width T of the ion gate voltage as follows:

[0056] The gas intake / exhaust in both vacuum subregions (10, 12) is adjusted while simultaneously monitoring the gas velocity v and vacuum pressure level. The gas velocity measurement consists of applying a gate voltage having a rectangular pulse waveform shape to the electrode 14 of the vDMS drift region and adjusting the waveform pulse width (and optionally the pulse frequency) until the ion detector signal begins to disappear. The rectangular pulse waveform acts as an ion shutter, applying gate voltage pulses to alternately open and close the vDMS drift region, thereby allowing and preventing ion passage through the drift region. The gate voltage waveform pulse width (and optionally the pulse frequency) at which the ion detector signal begins to disappear determines the minimum time window required for ions to pass completely longitudinally through the entire length of the drift region. The longitudinal length of the counter electrode 14, which defines the drift region, is known, thereby determining the total length of the drift region. Therefore, the ion velocity under these conditions can be calculated by calculating the ratio v = L / T between the longitudinal electrode length L and the gate voltage waveform pulse width T at which the ion detector signal begins to disappear.

[0057] The controller is configured to control a power supply (not shown) to apply gate voltage pulses having a controlled gate voltage pulse width T across an analytical gap g defined between opposing electrodes 14 of the vDMS assembly, such that the electrodes of the assembly act as an ion shutter. The controllers (22, 24) are configured to monitor the heights of ion mobility spectrum peaks detected by an ion detector, either stand-alone or within the mass analyzer assembly, within the downstream vacuum region 8. The controllers (22, 24) are configured to receive a signal 26 from the ion detector carrying the ion mobility peak height information to enable the controller to perform this monitoring process.

[0058] The control devices (22, 24) are configured to adjust the pulse width T of the gate voltage pulses applied to the electrodes 14 of the vDMS assembly so that the detected ion mobility spectrum peak (monitored via the signal 26) reaches a reduced height H2 that is lower than the maximum height H1 of the ion mobility spectrum peak detected during a current mobility spectrum peak height monitoring process. The reduced height H2 is determined according to a predetermined relative ratio R, R=H2 / H1. The control devices (22, 24) are configured to determine a velocity of the gas flow based on a ratio v of the pulse width T to the axial length L of the drift region, v=L / T.

[0059] The system is configured so that the predetermined relative ratio R has a value between 0.4 and 0.6, e.g., R=0.5. This ratio is chosen to represent the condition when the ion detector signal begins to disappear, as discussed above. It should be understood that the ion detector may exist in the downstream vacuum region as a standalone detector (e.g., for vDMS and FAIMS) or as part of a mass analyzer assembly. If the ion detector is part of a mass analyzer assembly, the mass filter function of the mass analyzer may optionally be turned off when measuring ion velocity, thereby allowing a higher throughput of ions entering the mass analyzer to reach the detector in order to obtain ion mobility peak height information, as described above. Of course, the mass filter function of the mass analyzer may be turned on once the desired velocity is achieved.

[0060] The process of change in shape and amplitude of the ion detector signal can be accurately modeled according to the modeling described in [3].

[0061] In this document, the peak shape and amplitude of the ion detector signal are

number

[0062] Buffer Gas Rate Control

[0063] The first vacuum region 6 comprises an upstream vacuum sub-region 10 containing an ion inlet (the outlet of the capillary 4) and another downstream vacuum sub-region 12 containing an ion outlet 16. The apparatus is configured to communicate gas flow between the upstream vacuum sub-region 10 and the downstream vacuum sub-region 12 through a drift region defined by a vDMS assembly (electrodes 14).

[0064] The controller (22, 24) includes an adjustable gas flow port 19 in the upstream vacuum sub-region 10 of the initial vacuum region, configured to allow an adjustable flow of gas (n5) therethrough into or out of the upstream vacuum sub-region 10 of the initial vacuum region. The controller is configured to adjust the adjustable gas flow port to vary the flow of gas therethrough, thereby varying the rate of gas flow (n5) into or out of the upstream vacuum sub-region 10.

[0065] Similarly, the controller (22, 24) includes a second adjustable gas flow port 20 in the downstream vacuum sub-region 12 of the first vacuum region, configured to allow an adjustable flow of gas (n5) therethrough into or out of the downstream vacuum sub-region 12 of the first vacuum region. The controller is configured to adjust the adjustable gas flow port to vary the flow of gas therethrough, thereby varying the rate of gas flow (n6) into or out of the downstream vacuum sub-region 12.

[0066] The initial vacuum region 6 is partitioned as described above, comprising an upstream vacuum sub-region 10 and a downstream vacuum sub-region 12 separated by an internal partition wall 11 within the initial vacuum region that separates the initial vacuum region into two sub-regions. The advantage of this partition is that it prevents the flow of buffer gas from the ion output end of the drift region of the vDMS assembly from flowing back into the ion input end of the drift region of the vDMS assembly. As a result, pressure control within the initial vacuum region 6 is easier.

[0067] For example, the controllers (22, 24) can be configured to decrease (or increase) the rate at which buffer gas flows through the analytical gap by simultaneously increasing (or decreasing) the rate at which gas flows out (e.g., pumping rate) from sub-region 10 and increasing (or decreasing) the rate at which external gas flows into sub-region 12.

[0068] The electrodes 14 of the vDMS device extend from the upstream vacuum subregion 10 through the interior partition wall 11 and into the downstream vacuum subregion 12. The drift region defined by the analytical gap g between the electrodes 14 of the vDMS device generates a gas flow rate n3 in the form of an inflow of gas flow from the ion source 2 as gas jets pass from the upstream vacuum subregion 10 and the downstream vacuum subregion 12. The upstream vacuum subregion 10 includes an adjustable gas flow port 19 configured to allow an upstream adjustable gas flow n5 to enter or exit the upstream vacuum subregion. The downstream vacuum subregion 12 includes an adjustable gas flow port 20 configured to allow an upstream adjustable gas flow n6 to enter or exit the downstream vacuum subregion. The skimmer exit port 16 in the initial vacuum region generates a gas flow rate n4 passing from the initial vacuum region 6 to the downstream vacuum region 8. Each of these gas flow rates n3, n4, n5, n6 is defined as the number of buffer gas particles per cubic meter flowing into / out of each region per second.

[0069] Assume that the background buffer gas particle density in the upstream vacuum sub-region 10 is N1 per cubic meter, and the background buffer gas particle density in the downstream vacuum sub-region 12 is N2 per cubic meter. The total particle density N of buffer gas particles per cubic meter in the initial vacuum region after gas has flown into / out of the initial vacuum region for a time Δt is

number

[0070] The total particle density N of the buffer gas is a measure of the buffer gas pressure. The cross-sectional area of ​​the drift region defined by the vDMS device, viewed perpendicular to the direction of buffer gas flow, is defined as A (m 2 ), and the velocity of the gas flow in the direction is v (m / s). Then, the vDMS device

number

number

[0071] To achieve a stable pressure value, the quantity N must not change over time.

number

number

[0072] Thus, for given stable values ​​of the buffer gas particle number density N3 in the drift region and the buffer gas particle number flow rate n4 entering the downstream vacuum region 8, the drift velocity v of the buffer gas and the velocity of the entrained ions along the drift region of the vMDS device can be controlled by controlling the buffer gas particle number flow rates n5 and n6 entering and / or exiting the initial vacuum region 6. Control of the buffer gas particle number flow rates n5 and n6 and calculation of the resulting buffer gas flow rate v are performed by a computer or microcontroller within the controller 24, as discussed above.

[0073] downstream IMS (e.g., LP-FAIMS / vDMS)

[0074] Once the desired buffer gas flow rate, v, and buffer gas pressure are achieved, a power supply (not shown) applies a distributed voltage waveform, V, to the electrodes 14 of the vDMS device. D By applying a dispersed electric field E across the analytical gap (g) between the electrodes, DThe power supply is configured to generate an AC distributed voltage waveform V so as to implement vDMS as described above with reference to FIG. D and DC voltage V C The power supply may be configured to generate the distributed voltage waveform 3 by a fast electronic switch that alternates between the high field (HF) and low field (LF) voltage amplitude extremes of the waveform 3 (see FIG. 1) provided by the power supply.

[0075] The control unit 24 controls the power supply and monitoring unit 22 to generate the distributed voltage V D Asymmetrical AC waveform 3 and DC compensation voltage V C to the electrode 14 in the drift region. D consists of a high field (HF) part and a low field (LF) part. This dispersion voltage V D is a distributed electric field E of alternating polarity that extends along the entire drift region, across the analytical gap g, and in a direction perpendicular to the long axis of the drift region. D =-(dV D (x) / dx)=-V D / g to produce a DC compensation voltage V C also has a compensation electric field E that extends along the entire drift region, across the analysis gap g, and in a direction perpendicular to the long axis of the drift region. C =-(dV C (x) / dx)=-V C Produces / g.

[0076] For example, the initial vacuum region 6 can comprise a vDMS device configured to function as an LP-FAIMS device 14 between the atmospheric pressure ionization (API) 2 and the mass analyzer (MS) stage 8. The electrospray ionization (ESI) source 2 can be configured to deliver a sample in a suitable solvent to the API to create a plume of charged droplets, as known in the art. At least some of the droplets enter a desolvation tube defined by a capillary 4, where they vaporize and release ions. The ions are carried in a supersonic gas jet of buffer gas and exit the capillary outlet toward the analytical gap g and along the drift region, entering an initial vacuum region of 1 mbar to 100 mbar. Electrodes 14 defining the drift region direct the ion-carrying buffer gas flow to an ion exit skimmer 16. Ion species with selected differential mobility values ​​pass through the ion exit skimmer 16 for further analysis by the mass analyzer 8. Other ion species that do not have the selected differential mobility value are deflected towards the FAIMS electrode 14 and are neutralized immediately upon landing on the electrode surface.

[0077] The pressure sensor 18 can be located in the drift region (as shown) or elsewhere in the initial vacuum region. The pressure sensor 18 can comprise a pressure gauge such as a diaphragm gauge or a Pirani cathode. A diaphragm gauge is preferred because no additional calibration for gas type is required. As mentioned above, the pressure measurement is preferably made in the initial vacuum chamber, far enough from the ion inlet capillary 4 to avoid pressure distortions of the supersonic gas jet, and far enough from the ion outlet skimmer 16, where the gas exiting the mass analyzer 8 forms a separate gas jet.

[0078] The example low pressure FAIMS (LP-FAIMS) shown in FIG. 2 can function in both a planar electrode configuration 14 defining the drift region and a multipole configuration (eg, 14b in FIG. 8).

[0079] Depending on the pumping rate through the skimmer 16 and the gas suction through the capillary 4, two cases arise. The first case is illustrated by the examples shown in Figures 3a-3d. In these examples, the suction of sample / buffer gas into the initial vacuum zone (104, 154, 204, 254) is greater than or equal to the suction of gas (116, 166, 216, 266) into the downstream vacuum zone (108, 158, 208, 258) through the skimmer. The second case is illustrated by the examples shown in Figures 4a-4d. In these examples, the suction of sample / buffer gas into the initial vacuum zone (304, 354, 404, 454) is less than or equal to the suction of gas (316, 366, 416, 466) into the downstream vacuum zone (308, 358, 408, 458) through the skimmer. It should be understood that although not explicitly shown in Figures 3a-3d or 4a-4d, the components shown in the device of Figure 2, such as pressure sensor 18, gas flow control assembly (19, 20), gas pressure monitoring unit 22, processor unit 24, etc., are actually included and configured to operate as described herein with reference to Figure 2, but have been omitted from Figures 3a-3d and 4a-4d solely for the sake of clarity.

[0080] In the example experiment shown in Figure 3b, a sample of glutamine and lysine was delivered from an electrospray source 152 and entered a capillary 154 into an upstream vDMS chamber 160. The sample, carried by a buffer gas flow, traveled between electrodes 164 into a downstream vDMS chamber 162. From the downstream chamber 162, the sample, along with the buffer gas, was transported through a skimmer 166 into a single quadrupole mass analyzer 158. The pressure in the vDMS 156 was set to a value ranging from 10 to 40 mbar. The total pressure in the vDMS was measured by diaphragm gauges 168 and 170 on both chambers. The pressure difference between chambers 160 and 162 was less than the accuracy of the diaphragm gauges. The internal pressure was initially regulated by a valve 174 connected to a roughing pump. The required vDMS operating pressure P (e.g., for a given experiment) was then adjusted. rwas adjusted by adding nitrogen (N2) gas through valve 176, a mass flow controller operated by a computer that reads pressure from vacuum gauges 168 or 170. The initial adjustment through valve 174 was made because the pressure range achievable through mass flow controller inlet 176 was limited. Mass flow controller inlet 176 was used because it provided more precise control of the vacuum level than the motorized valve connected to the roughing pump.

[0081] To measure the gas velocity within the vDMS, the waveform generator was disconnected from the electrode 14. A square ion gate pulse waveform generator was connected to the electrode 14 of the vDMS assembly. Figure 5a shows the signal (520) from the ion detector in the mass analyzer 158 when connected to an oscilloscope, along with the signal (510) from the square waveform generator and the reference signal (500) from the electrode. The pulse width T of the ion gate signal was set to a longer value (lower pulse frequency) to open the electrode for a longer time to the ions, and the height of the flat ion peak was measured via the ion detector signal. To find the transit time of the ions (and buffer gas) through the drift region, the pulse width T of the ion gate signal 530 was set to a shorter value (higher pulse frequency) in the pulse generator, and the value of T was adjusted until the peak in the signal 550 from the ion detector in the mass analyzer 158 was reduced to 50% of the previous maximum peak height, as shown in Figure 5b. This value of 50% of the initial maximum peak was chosen as the expected height of the ion signal peak observed when the mean value of the buffer gas velocity distribution coincided with the minimum gas velocity required for ions to traverse the length of the drift region between successive applications of the ion gate signal applied to the electrodes 14 of the vDMS assembly. This ion gate signal pulse frequency minimized the time required for the gate formed between the electrodes of the vDMS assembly to open and allow ions to pass, thus determining the ion transit time. Since the length of the electrodes 14 of the vDMS assembly is known, the average gas velocity can be calculated based on this.

[0082] To reach the target gas velocity, the regulation loop comprising steps a) to c) is carried out as described above. This process involves opening the pre-chamber valve 172 to increase the pumping rate therein, and then increasing the pressure until it reaches the target P r This involves waiting for the gas pressure to return to a value (which is achieved by a computer operated mass flow controller through inlet 176) and then performing a gas velocity measurement.

[0083] 3a-3d relate to the case where the suction 104, 154, 204, 254 of sample / buffer gas is greater than or equal to the pumping rate through the skimmer 116, 166, 216, 266 into the downstream vacuum region 108, 158, 208, 258. FIG.

[0084] 3a shows an assembly with a valve 122 in the front chamber 110 connected to a roughing pump, and a valve 124 in the rear chamber 112 connected to a roughing pump. Both valves 122, 124 can be motorized to reduce the pumping rate from the roughing pump. The difference in pumping rate between the chambers 110, 112 can be adjusted through these valves 112, 124 without the need for additional N2 injection. The same principles as described above can be used to set the buffer gas velocity and pressure P r Maintain.

[0085] Figure 3b shows an assembly with a valve 172 in the front chamber 160 connected to a roughing pump, and a valve 174 in the back chamber 162 connected to a roughing pump. To regulate the pressure with greater precision, an additional gas inlet 176 that can be operated by a mass flow controller has been added to the back chamber 162. Both valves 172, 174 can be motor driven to reduce the pumping rate from the roughing pump. The difference in pumping rate between the chambers 160, 162 can be adjusted through the valves 172, 174 together with the additional buffer gas (N2) inlet 176. Using the same principles as described above, the buffer gas rate can be set to control the pressure P r Maintain.

[0086] Figure 3c shows an assembly with a valve 222 in the antechamber 210 connected to a roughing pump, and a valve 224 in the post-chamber 212 connected to a roughing pump. To regulate the pressure with greater precision, an additional gas inlet 228 has been added to the antechamber 210, which can be operated by a mass flow controller. Both valves 222, 224 can be motor-driven to reduce the pumping rate from the roughing pump. The pumping rate difference between the chambers 160, 162 can be adjusted through the valves 222, 224 together with the additional buffer gas (N2) inlet 228. Using the same principles as described above, the buffer gas rate can be set to control the pressure P r Maintain.

[0087] Figure 3d shows an assembly with a valve 272 in the front chamber 260 connected to a roughing pump, and a valve 274 in the back chamber 262 connected to a roughing pump. To regulate the pressure with greater precision, an additional gas inlet 278 that can be operated by a mass flow controller has been added to the front chamber 228, and an additional gas inlet 276 has been added to the back chamber 262. Both valves 272, 274 can be motorized to reduce the pumping rate from the roughing pump. The difference in pumping rate between the chambers 260, 262 can be adjusted through the valves 272, 274 along with the additional buffer gas (N2) inlets 278 and 276. Using the same principles as described above, the buffer gas rate can be set to control the pressure P r Maintain.

[0088] 4a-4d relate to the case where the sample / buffer gas suction 304, 354, 404, 454 is greater than or equal to the gas suction through the skimmer 316, 366, 416, 466 into the downstream vacuum region (308, 358, 408, 458).

[0089] 4a shows an assembly with an inlet 328 in the pre-chamber 310 and an inlet 326 in the post-chamber 312. Either inlet 328, 326 can be used with a mass flow controller and N injection. The pumping rate difference between the chambers 310, 312 can be adjusted through these inlets 328, 326 without an additional outlet with a valve to the roughing pump. The same principles as described above can be used to set the buffer gas velocity and pressure P r Maintain.

[0090] Figure 4b shows an assembly with an inlet 378 in the front chamber 360 and an inlet 376 in the back chamber 362. Both inlets 378, 376 can be used with mass flow controllers and N2 injection. The pumping rate difference between the chambers 360, 362 can be adjusted through these inlets 378, 376, along with an additional outlet 374 in the back chamber that has a valve to a roughing pump. The valves can be motor driven. The same principles as described above can be used to set the buffer gas velocity and pressure P r Maintain.

[0091] Figure 4c shows an assembly with an inlet 428 in the antechamber 410 and an inlet 426 in the post-chamber 412. Either inlet 428, 426 can be used with a mass flow controller and N2 injection. The pumping rate difference between the chambers 410, 412 can be adjusted through the inlets 428, 426, along with an additional outlet in the antechamber 410 with a valve to a roughing pump. The valves can be motor driven. The same principles as described above can be used to set the buffer gas velocity and pressure P r Maintain.

[0092] Figure 4d shows an assembly with an inlet 478 in the pre-chamber 460 and an inlet 476 in the post-chamber 462. Either inlet 478, 476 can be used with a mass flow controller and N2 injection. The pumping rate difference between the chambers 460, 462 can be adjusted through the inlets 478, 476, along with an additional outlet in the pre-chamber 410 and an additional outlet 474 in the post-chamber, both of which have valves to a roughing pump. Each valve can be motor driven. The same principles as described above can be used to set the buffer gas velocity and pressure P r Maintain.

[0093] Heat maps of the ion signal intensities of glutamine and lysine versus the buffer gas are shown in Figures 7(a) and (b). These figures show the dispersion electric field strength E versus the neutral buffer gas particle number density N. D The ratio of E D / N, the compensation electric field strength E for the neutral buffer gas particle number density C The ratio of E C When / N is set, E D / N vs E C The unit of E / N is Townsend (Td), where 1Td = 10 -17 Vcm 2 The data are for a mixture of glutamine and lysine measured in the vDMS at a buffer gas pressure of 32 mbar. Figure 7(a) shows the results of a measurement performed with an instrument configuration without gas velocity control at 25 m / s, resulting in a resolution of 3. Figure 7(b) shows the results of a measurement performed as described above, with the buffer gas velocity v reduced to v = 2.6 m / s, thereby resulting in an ion mobility resolution of 11.

[0094] The present invention allows for adjustment of buffer (and ion) velocity in jet-driven LP-FAIMS / vDMS instruments. This has several advantages. One advantage is increased resolution. Another advantage is improved transmission. The present invention allows for adjustment of gas velocity while maintaining a vacuum within the instrument for a given geometry of the LP-FAIMS / vDMS instrument. For a given geometry of the LP-FAIMS / vDMS instrument, the gas velocity into the initial vacuum region can also be determined by the geometry near the exit of the ion source. This gas pressure typically depends on the operating pressure of the LP-FAIMS / vDMS in the drift region. However, the optimal pressure for the LP-FAIMS / vDMS varies for different ion species. Prior art systems do not allow for independent variation of the LP-FAIMS / vDMS pressure and gas velocity, and therefore do not allow for full optimization of the LP-FAIMS / vDMS instrument for various types of sample ions. The present invention enables this optimization.

[0095] Ion separation efficiency depends on how many waveform cycles the ions can undergo, and one of the factors is the velocity of the buffer gas that carries the transported ions. Increasing the residence time of the ions in the drift region results in better ion separation and increased resolution. This can be achieved by reducing the buffer gas velocity without affecting the vacuum level in the drift region between the electrodes.

[0096] Higher resolution can be achieved by reducing the gas velocity through the LP-FAIMS / vDMS instrument. Ions are transported through the LP-FAIMS in a gas flow; that is, they are carried in a gas jet, and the ion velocity and gas velocity can be considered equal. Achieving the same gas velocity at different vacuum levels is also important for consistent measurements.

[0097] In existing vacuum DMS instruments (vDMS), the buffer gas velocity is dependent on the pressure of the vacuum region containing the ion stream and cannot be adjusted on demand. These instruments require high gas velocities, which significantly reduce resolution. Maintaining a constant gas velocity for any desired vacuum value within the available range is important for consistent measurements, and the present invention allows users to set the buffer gas velocity on demand for a given vacuum value within the instrument. The present invention uses pressure regulation and gas pumping in the context of a jet-driven gas flow, associated with an API source, and a process for controlling the buffer gas velocity in an IMS instrument (e.g., LP-FAIMS / vDMS) to provide higher resolution.

[0098] FIG. 6 shows a method for analyzing ions by ion mobility spectrometry (IMS) according to a process comprising the following steps:

[0099] Step 1: Ions are generated from a sample in an ion source and carried in a buffer gas (preferably the buffer gas is a supersonic jet) and delivered into an ion mobility spectrometer within a vacuum region that includes an ion drift region formed between electrodes that define an analytical gap.

[0100] Step 2: Prior to performing differential ion mobility analysis of said ions, a) varying the flow rate of gas into or out of said vacuum region; b) measuring the gas pressure within the vacuum region; The steps a) and b) are repeated until the measured gas pressure value reaches a predetermined target gas pressure value.

[0101] Step 3: After step 2, c) measuring the velocity of gas flow along said drift region as described herein; Steps a) through c) are repeated until the measured gas velocity value reaches a predetermined target gas velocity value.

[0102] Step 4: After step 3, perform a differential ion mobility analysis of the transported ions based on the target gas pressure value and the target gas velocity value.

[0103] Referring to FIG. 2, upon entering the initial vacuum region 6, ions and neutral buffer gas particles form a jet. A conical or bell-shaped gas flow shaping element 15 may optionally be used to shape the gas flow and direct it through the elongated electrode array that makes up the FAIMS device. This is shown schematically in FIG. 8. The downstream vacuum region 8 can be maintained at a lower pressure than the initial vacuum region by a pump (not shown). Instead of the flat electrode assembly shown in FIG. 2, a decadelodeon electrode assembly, for example, may be used as the FAIMS device 14b. By matching the inlet diameter of the conical gas flow shaper 15 to the diameter of the inlet capillary 4 and matching the outlet diameter of the conical gas flow shaper 15 to the inlet diameter of the cylindrical decadelodeon 14b, smooth passage of the gas entering the initial vacuum region is achieved. It should be understood that this alternative arrangement is also applicable to the examples described above with reference to FIGS. 3a-3b and 4a-4d.

[0104] Each feature disclosed in the foregoing description, the following claims, or the accompanying drawings is, where appropriate, expressed in its specific form or in terms of a means for performing a disclosed function or a method or process for obtaining a disclosed result, but the features can be utilized individually or in any combination of several features to realize the invention in various forms thereof.

[0105] While the present invention has been described above in connection with exemplary embodiments, many equivalent modifications and variations will be apparent to those skilled in the art in light of this disclosure. Accordingly, the exemplary embodiments of the present invention set forth above should be considered illustrative and not limiting. Various changes can be made to the embodiments without departing from the spirit and scope of the present invention.

[0106] For the avoidance of doubt, any theoretical explanations provided herein are intended to enhance the understanding of the reader, and the inventors do not wish to be bound by any of these theoretical explanations.

[0107] The headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described.

[0108] Throughout this specification, including the claims which follow, the words "comprise" and "include," and variations thereof (such as "comprises," "comprising," and "including"), unless the context otherwise requires, shall be interpreted as meaning the inclusion of stated integers or steps or groups of integers or steps, but not to the exclusion of other integers or steps or groups of integers or steps.

[0109] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. When ranges are expressed in this specification, the term "about" may be used to refer to a particular starting value and / or to another particular ending value. When such ranges are expressed, the ranges where the particular starting value is the exact starting value and / or the other particular ending value constitute another embodiment. Similarly, when values ​​are expressed as approximations by use of the antecedent "about," it should be understood that the particular values ​​constitute another embodiment. The relationship between the term "about" and the numerical values ​​is arbitrary, and may mean, for example, ±10%.

[0110] References

[0111] A number of publications have been cited above in order to more fully describe and disclose the present invention and the state of the art to which it pertains. A complete list of the cited publications is set forth below. The entirety of each of these references is incorporated herein by reference. A. Buryakov, et al., Int. J. Mass Spectrom. Ion Processes 1993, 128, p143 R. W. Purves, et al., Rev. Sci. Instrum. 1998, 69, p4094 G. E. Spangler and C. I Collins, “Peak Shape Analysis and Plate Theory for Plasma Chromatography”, Analytical Chemistry, Vol. 47, No. 3, March 1975. US 8610054 B2 US 8084736 B2

Claims

1. generating ions from a sample in an ion source; delivering the ions through an ion inlet into a vacuum region of a vacuum enclosure comprising a differential ion mobility spectrometer comprising an ion drift region formed between opposing electrodes defining an analytical gap, wherein the ions emerge from the ion inlet and into the drift region as a supersonic jet of buffer gas in which the ions are carried; and delivering the ions from the differential ion mobility spectrometer to an ion detector to generate one or more ion mobility spectrum peaks; An ion analysis method comprising: a) varying the flow rate of gas into or out of said vacuum region; b) measuring the gas pressure within the vacuum region and comparing the measured gas pressure value with a target gas pressure value; repeating steps a) and b) until the gas pressure comparison indicates that the measured gas pressure value has reached the target gas pressure value; c) measuring the velocity of gas flow along the drift region by applying a gate voltage pulse across the analytical gap to act as an ion shutter, detecting an ion mobility spectrum peak produced by the ion detector, adjusting the pulse width of the gate voltage pulse so that the detected ion mobility spectrum peak reaches a reduced height (H2) that is lower than a maximum detected height (H1) of the ion mobility spectrum peak, the reduced height (H2) being in accordance with a predetermined relative ratio R, such that R=H2 / H1, and determining the velocity of the gas flow as v=L / T based on the ratio v of the pulse width T to the axial length L of the drift region; repeating steps a) to c) until the measured gas velocity value reaches a predetermined target gas velocity value, and then performing a differential ion mobility analysis using the differential ion mobility analyzer based on the target gas pressure value and the target gas velocity value. A method comprising:

2. 2. The method of claim 1, further comprising, after the differential ion mobility analysis by the ion mobility spectrometer, delivering the ions from the vacuum region through an ion outlet into a downstream vacuum region of the vacuum enclosure and performing mass spectrometry analysis of the ions in that region.

3. 3. The method of claim 1, wherein the predetermined relative ratio R has a value between 0.4 and 0.

6.

4. 4. The method of claim 1, wherein the vacuum region comprises an upstream vacuum sub-region including the ion inlet and another downstream vacuum sub-region including the ion outlet, the method comprising communicating a gas flow between the upstream vacuum sub-region and the downstream vacuum sub-region via the drift region.

5. 5. The method of any preceding claim, wherein varying the flow rate of gas into or out of the vacuum region comprises providing an adjustable gas flow port in the vacuum region, separate from the ion inlet and the ion outlet, the adjustable gas flow port configured to allow an adjustable flow of gas to enter or exit the vacuum region therethrough, the method comprising adjusting the adjustable gas flow port to vary the flow of gas therethrough.

6. 6. A method according to claim 5 when dependent on claim 4, wherein varying the flow rate of gas into or out of the vacuum region comprises providing each of the upstream vacuum sub-region and the downstream vacuum sub-region with a respective adjustable gas flow port configured to allow an adjustable flow of gas to enter or exit the upstream vacuum sub-region or the downstream vacuum sub-region therethrough, the method comprising adjusting each adjustable gas flow port to vary the flow of gas therethrough.

7. 1. An ion analyzer comprising an ion source configured to generate ions from a sample and an ion detector, wherein in use ions travel along an ion optical axis from the ion source to the ion detector, the ion analyzer further comprising: A vacuum enclosure containing a differential ion mobility spectrometer including a vacuum region with an ion inlet and an ion outlet, the vacuum region having an ion drift region formed between opposing electrodes defining an analytical gap. Equipped with the ion source is configured to deliver the ions through the ion inlet into the vacuum region such that the ions emerge from the ion inlet and enter the drift region as a supersonic jet of buffer gas in which the ions are carried, and in use ions generated from the sample are subjected to differential ion mobility analysis, the differential ion mobility spectrometer being configured thereafter to deliver the ions to the ion detector to produce one or more ion mobility spectral peaks; The ion analyzer is a) varying the flow rate of gas into or out of said vacuum region; b) measuring the gas pressure within the vacuum region and comparing the measured gas pressure value with a target gas pressure value; repeating steps a) and b) until the gas pressure comparison indicates that the measured gas pressure value has reached the target gas pressure value; c) measuring the velocity of gas flow along the drift region by applying a gate voltage pulse across the analytical gap to act as an ion shutter, detecting an ion mobility spectrum peak produced by the ion detector, adjusting a pulse width T of the gate voltage pulse so that the detected ion mobility spectrum peak reaches a reduced height H2 that is lower than a maximum detected height H1 of the ion mobility spectrum peak according to a predetermined relative ratio R, such that R=H2 / H1, and determining the velocity of the gas flow based on a ratio v of the pulse width T to an axial length L of the drift region, as v=L / T; repeating steps a) through c) until the measured gas velocity value reaches a predetermined target gas velocity value. a controller configured to perform the process of The ion analysis device is then configured to perform the differential ion mobility analysis based on the target gas pressure value and the target gas velocity value.

8. 8. The apparatus of claim 7, wherein the evacuated enclosure comprises a downstream vacuum region containing a mass analyzer, and the ion outlet is configured to deliver ions from the vacuum region into the downstream vacuum region for mass spectrometric analysis of the ions.

9. 9. The measure according to claim 7 or 8, wherein the predetermined relative ratio R has a value between 0.4 and 0.

6.

10. 10. The apparatus of claim 7, wherein the vacuum region comprises an upstream vacuum sub-region including the ion inlet and another downstream vacuum sub-region including the ion outlet, the apparatus being configured to communicate gas flow between the upstream and downstream vacuum sub-regions via the drift region.

11. 11. The apparatus of any of claims 7 to 10, comprising an adjustable gas flow port in the vacuum region separate from the ion inlet and the ion outlet, the adjustable gas flow port being configured to allow an adjustable flow of gas to enter or exit the vacuum region through the adjustable gas flow port, and the controller being configured to adjust the adjustable gas flow port to vary the flow of gas therethrough and thereby vary the rate of gas flow into or out of the vacuum region.

12. 12. The apparatus of claim 11 when dependent on claim 10, wherein each of the upstream and downstream vacuum sub-regions comprises a respective adjustable gas flow port configured to allow an adjustable flow of gas to enter or exit the upstream or downstream vacuum sub-region therethrough, and wherein the controller is configured to vary the flow rate of gas into or out of the respective upstream or downstream vacuum sub-region to vary the flow rate of gas into or out of the vacuum region.

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