Ion shutter, ion shutter control method, and detection method and device

Abstract

1. A method of operating an ion mobility spectrometer, the method comprising the steps of: drawing a gaseous fluid sample into a reaction region of the ion mobility spectrometer; providing a first pulse of a pulsed source to ionize the gaseous fluid sample, thereby obtaining first sample ions; opening an ion shutter after a first gate delay after a first trigger to allow some of the first sample ions to exit the reaction region; providing a second pulse of the pulsed ionization source to further ionize the gaseous fluid sample, thereby obtaining second sample ions; and opening the ion shutter after a second gate delay after the first trigger to allow some of the second sample ions to exit the reaction region, the second gate delay being different from the first gate delay.

Description

[Technical Field]

[0001] The present invention relates to methods and apparatus, particularly to methods and apparatus for analyzing materials by detecting ions, and more particularly to ion shutters for such apparatus and methods for controlling such ion shutters. [Background technology]

[0002] Ion mobility spectrometers (IMS) can identify materials from a sample of interest by ionizing the material (e.g., molecules, atoms, etc.) and measuring the time it takes the resulting ions to travel a known distance under a known electric field. Typically, this time is measured from the time an ion gate (which may also be called an ion shutter) is opened to the time the ions reach a detector such as a Faraday cup.

[0003] The time-of-flight of each ion is related to the ion's mobility, which in turn is related to its mass and geometric shape. Therefore, by measuring the time-of-flight of an ion, it is possible to infer its identity. These times-of-flight can be displayed graphically or numerically as a spectrum.

[0004] As mentioned above, some IMS cells include a detector that collects ions to measure their time of flight so they can be identified. This can be done in the presence of a drift gas, allowing mobility effects to separate ions. Some IMS cells can separate ions according to their time of flight, so that ions with selected time-of-flight (meaning a selected range of ion mobilities) can be provided to other detector instruments, such as a mass spectrometer, for further analysis. One example of this technique is known as IMS-MS, in which an IMS cell is used as an ion filter to select ions from a sample. The selected ions are then provided to a mass spectrometer. In such ion identification or filtering methods, groups of ions can be ejected from the reaction region by opening an ion shutter and / or passed through the entrance to the mass spectrometer.

[0005] The reaction region of an IMS cell has a finite length, and during the interval that the shutter is held open, ions that may be distributed around the reaction region must travel (at least partially) across the reaction region to reach the shutter.

[0006] The opening of the shutter in a pulsed ionization source IMS spectrometer is typically synchronized with the generation of the ion pulse. This synchronization involves a so-called "gate delay" that occurs a fixed time after the ion pulse is generated. This delay is required so that the ion pulse is present at the shutter when the shutter is opened.

[0007] It is possible to operate the spectrometer without a shutter or to leave the shutter open continuously, however, it has been found that ungated corona-generated pulses result in broad, poor resolution. Summary of the Invention [Problem to be solved by the invention]

[0008] Aspects and embodiments of the present invention are claimed that allow the normally fixed gate delay to be varied to improve the response of the IMS to the material of interest.

[0009] For example, one problem that can be addressed by the present disclosure is the gate delay selecting which ions from any given pulse of the ionization source are accepted by the detector. Due to mobility effects in the reaction region, shorter delays tend to allow more of the smaller, more mobile ions into the drift region. On the other hand, longer gate delays may promote the admittance of lower mobility ions into the drift region. More mobile ions can include so-called reactant ions, while less mobile ions can include product ions.

[0010] To address this problem of mobility selection, the gate delay can be set so that both the reactant ion peak (RIP) and the product ions are visible in a typical sample spectrum. Such a "middle ground" setting of the gate delay can exclude some of the product ions from entering the drift tube, thus reducing the apparent sensitivity of the detector to this type of ion.

[0011] The disclosed embodiments aim to improve the apparent sensitivity of IMS detectors and reduce the above-mentioned problem of "mobility selection."

[0012] Other issues can also be addressed by the ion shutter control techniques described herein. [Means for solving the problem]

[0013] In one aspect, a method of operating an ion mobility spectrometer is provided, the method comprising: drawing a sample of the gaseous fluid into a reaction volume of said ion mobility spectrometer; providing a first pulse of a pulsed ionization source to ionize the sample of gaseous fluid, thereby obtaining first sample ions; opening an ion shutter after a first gate delay following a first trigger to allow a portion of the first sample ions to exit the reaction region; providing a second pulse of the pulsed ionization source to further ionize the sample of gaseous fluid, thereby obtaining second sample ions; opening the ion shutter after a second gate delay following a first trigger to allow a portion of the second sample ions to exit the reaction region, the second gate delay being different from the first gate delay.

[0014] The second gate delay can be selected so that a portion of the second sample ions includes reactant ions rather than product ions. The first gate delay can be longer than the second gate delay. The first gate delay can be selected so that a portion of the first sample ions includes product ions in preference to reactant ions.

[0015] These and other methods described herein include obtaining ion spectral data based on analyzing at least one of (a) a portion of the first sample ions and (b) a portion of the second sample ions, whereby subsequent operation of an ion shutter of an ion mobility spectrometer can be controlled based on said analysis of at least one of (a) and (b).

[0016] Controlling subsequent actuation of the ion shutter can include selecting a subsequent gate delay based on a product ion peak in the acquired ion spectrum data. For example, selecting the next gate delay can include selecting a gate delay to increase the amplitude of the product ion peak, e.g., by selecting a gate delay that allows a greater number of ions having that mobility range to pass through the gate. While the exact time at which an ion species travels from the ion source to the gate generally cannot be analytically defined for all systems, those skilled in the art will understand in the context of this disclosure that for any given system, it is possible to empirically determine a range of gate delays that is suitable for increasing sensitivity to ions of a particular mobility.

[0017] Controlling subsequent actuation of the ion shutter may include reducing the gate width during a gate delay interval associated with the product ion peak. In addition to, or as an alternative to, selecting a gate delay for sensitivity to a particular ion species that may be expected in the sample, one or more of the gate delays used in an array of such delays may be selected based on the mobility of a calibrant, for example, to enhance a calibrant peak.

[0018] Drawing a sample of the gaseous fluid may include activating a pressure pulser to draw the sample into the reaction region, wherein a first pulse of the ionization source and a second pulse of the ionization source are both performed before a next activation of the pressure pulser.

[0019] The method described herein comprises: determining first ion spectral data based on analyzing the first sample ions; determining a second ion spectrum based on analyzing the second sample ions; and Combining the first ion spectral data and the second ion spectral data to provide a combined spectrum for identifying a substance of interest in the sample of gaseous fluid. may include:

[0020] One aspect provides a detector that includes: a pulsed ionization source for ionizing the gaseous fluid in the reaction region of the detector instrument; ion shutter; Controllers capable of operating: activating the pulsed ionization source to provide a first pulse that ionizes a sample of gaseous fluid in the reaction region, thereby obtaining first sample ions; controlling the ion shutter to provide a first gate delay between activation of the ionizer and opening of the ion shutter to allow a portion of the first sample ions to exit a reaction region; activating the pulsed ionization source to provide a second pulse to further ionize the sample of gaseous fluid in the reaction region, thereby obtaining second sample ions; controlling the ion shutter to provide a second gate delay between activation of the ionizer and opening of the ion shutter to allow a portion of the second sample ions to exit the reaction region; Here, the second gate delay is different from the first gate delay.

[0021] The second gate delay may be selected so that a portion of the second sample ions includes reactant ions rather than product ions. The first gate delay may be longer than the second gate delay. The first gate delay may be selected so that a portion of the first sample ions includes product ions in preference to reactant ions. The controller may be configured to obtain ion spectrum data based on analyzing at least one of (a) a portion of the first sample ions and (b) a portion of the second sample ions. The controller may be configured to control subsequent operation of the ion shutter based on the analysis, for example, to select a subsequent gate delay based on the timing of a product ion peak in the acquired ion spectrum data. Selecting a subsequent gate delay may include selecting a gate delay to increase sensitivity to a product ion peak (e.g., to increase the amplitude achievable with a given gate width). Controlling subsequent operation of the ion shutter may include reducing the gate width during a gate delay interval associated with the product ion peak.

[0022] At least one gate delay may be selected based on the mobility of the calibrant.

[0023] The detectors described herein may include a pressure pulser (e.g., an electromechanical actuator that drives a diaphragm in the manner of a loudspeaker). Such a pressure pulser may be configured to provide a sample of gaseous fluid from an inlet of the instrument to the reaction region. Drawing the sample of gaseous fluid includes activating the pressure pulser to draw the sample into the reaction region, for example, by temporarily reducing the pressure within the reaction region. The controller may be configured such that after activating the pressure pulser to draw the sample into the reaction region, both a first pulse of the ionization source and a second pulse of the ionization source are performed before the next activation of the pressure pulser.

[0024] One aspect provides a method of configuring an ion mobility spectrometer, the method comprising: A program for a controller of the apparatus to carry out any of the methods described or claimed herein.

[0025] It will be understood that in the context of the present disclosure, such a controller may be connected to control the pulsed ionization source and ion shutter of the apparatus, and / or connected to the detector of the apparatus for obtaining ion spectrum data, and / or connected to control the pressure pulser of the apparatus for providing a sample of gaseous fluid into the reaction region.

[0026] One aspect of the present disclosure provides a computer program product, such as a computer readable signal or a tangible non-transitory computer readable storage medium, that includes program instructions for programming a controller of an ion mobility spectrometry apparatus to perform any of the methods described or claimed herein.

[0027] Any feature of any one of the embodiments disclosed herein can be combined with any selected feature of any of the other embodiments described herein. For example, method features can be implemented in appropriately configured hardware, and specific hardware configurations described herein can be employed in methods implemented using other hardware.

[0028] Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 shows a cross-sectional view of an ion mobility spectrometer. [Figure 2] FIG. 2 is a flow chart illustrating the method of operation of such an ion mobility spectrometer. [Figure 3] FIG. 3 shows a schematic diagram of an example of an ion mobility spectrometer of the type shown in FIG. [Figure 4]FIG. 4 is a timing diagram illustrating the operation of such an ion mobility spectrometer to carry out a method of the type illustrated by FIG. [Figure 5] FIG. 5 is a flow chart illustrating a method of operation as described with reference to FIG. 2 and / or FIG. [Figure 6] FIG. 6 is a flow chart illustrating a further such method of operating an ion mobility spectrometer. DETAILED DESCRIPTION OF THE INVENTION

[0030] In the drawings, like reference numbers are used to indicate like elements.

[0031] (Specific explanation) FIG. 1 shows a cross-sectional view of an ion mobility spectrometer, which includes a reaction region 102, a pulsed ionization source 104 for ionizing a gaseous fluid within the reaction region 102, an ion shutter 105, and a controller 120.

[0032] Controller 120 is connected to ionization source 104 and shutter 105. In typical operation, each time a sample of gaseous fluid (e.g., vapor) is supplied to the reaction region, controller 120 supplies a series of pulses of ionization source 104. Following each pulse, controller 120 opens ion shutter 105 after a "gate delay," and ions generated by that pulse then travel from the reaction region along the drift region of the spectrometer to a detector, such as a Faraday cup. Each actuation pulse of ionization source 104 can thus be used to provide an ion mobility spectrum. The series of spectra resulting from the series of pulses applied to each sample are then combined to provide the spectrum for that sample.

[0033] 1 is configured to vary the gate delay so that a different gate delay is used for at least one pulse in the series of pulses. The ion mobility spectrum generated by combining spectra generated using different gate delays reduces problems that might otherwise be caused by "mobility selection."

[0034] We now describe an entire ion mobility spectrometry (IMS) cell to put into context the subsequent discussion of how to adequately address these and other issues.

[0035] The IMS cell comprises a housing such as a tube 101. A reaction region 102 is at one end inside this housing 101 and is separated from a detector 118 by a drift region 103. The reaction region 102 is separated from the drift region 103 by an ion shutter 105. The housing 101 includes an inlet 108 to allow a sample of gaseous fluid (such as a vapor, and / or gas, and / or aerosol) to be introduced into the reaction region 102.

[0036] The pulsed ionization source 104 is positioned to ionize the sample within the reaction region. In the embodiment shown in FIG. 1 , the pulsed ionization source 104 includes a corona point. The pulsed ionization source 104 is connected such that the controller 120 can control the delivery of electrical energy to the controller 120, such as by switching on the supply of pulses of electrical power. In the context of the present disclosure, it will be understood that each pulse of operation of the ionization source 104 may include a period during which a series of voltage spikes are applied across the electrodes of the ionization source 104. For example, the ionization source 104 may have some capacitance, and thus delivery of a short DC pulse may result in some “ringing.” Thus, application of a pulse by the ionization source 104 may include switching the ionization source 104 from an “off” state to an active state, where ions are sometimes generated by a series of voltage spikes (e.g., generated by an AC voltage that may be associated with such ringing) before being returned to the “off” state.

[0037] The ion shutter 105 comprises two electrodes 106, 107, which are coupled to a controller 120 to allow a barrier voltage to be provided between the two electrodes 106, 107. When the shutter 105 is "closed," this barrier voltage acts to prevent ions from traveling from the reaction region to the drift region of the IMS, and in an open state, ions can travel to the drift region toward the detector. The ion shutter 105 may comprise a Tyndall-Powell, Bradbury-Nielsen, or other type of shutter. The shutter electrodes 106, 107 may each comprise elongated conductors, and the elongated conductors of the first shutter electrode 106 may be aligned in the drift direction with the elongated conductors of the second shutter electrode 107. The elongated conductors of each shutter electrode 106, 107 may be arranged as a mesh, e.g., a grid, such as a triangular, rectangular, hexagonal, or other regular or irregular mesh. As will be explained below, the shutter electrodes 106, 107 do not have to be separated in the drift direction, for example they may be coplanar, in which case the elongated conductors may be interdigitated, e.g., interdigitated or interwoven.

[0038] 1, the drift region 103 is between the reaction region 102 and a detector 118, such as a current collector, e.g., a Faraday cup for detecting the arrival of ions, or another type of detector 118, such as a mass spectrometer. If such another type of detector is used, the inlet of that detector may be used instead of the Faraday cup, and an additional ion shutter may be inserted between the drift region and the inlet of that detector. This can be used to select (e.g., filter) ions that are provided to the other detector according to their time of flight.

[0039] A voltage profile may be provided to the drift region 103 using a series of drift electrodes 103a, 103b spaced along the drift region. Although not shown in FIG. 1 , a repeller plate or other electrode may be positioned to extend this voltage profile into the reaction region 102. Between the reaction region 102 and the detector 118, the profile voltage varies spatially (e.g., as a function of displacement along the cell in the drift direction) to provide an electric field that moves ions along the cell 100 toward the detector 118. The electric field may be uniform and / or known along the drift region 103 and / or the reaction region 102.

[0040] The controller 120 comprises a programmable processor and an output interface, such as a DAC (not shown), that can control the supply of appropriate electrical control signals and / or power to the ion shutter and ionization source 104. Thus, the controller 120 is operable to operate the pulsed ionization source 104 and control the ion shutter. The controller 120 may also store timing data indicative of gate delays associated with particular types of ions. For example, it may include data indicative of gate delays associated with preferentially selecting reactant ions and / or other types of ions, such as calibrant ions.

[0041] The IMS cell 100 shown in FIG. 1 may also include a drift gas inlet 122 to the drift region near the detector and a drift gas outlet near the shutter, so that a flow of (cleaned and dried) drift gas can be provided in the direction of ion movement toward the detector.

[0042] Next, the operation of the IMS cell shown in FIG. 1 will be described with reference to FIG.

[0043] In operation, a sample of gaseous fluid, such as a steam, is provided 300 into the reaction region 102. The controller 120 then triggers the provision of power to the pulsed ionization source 104, which provides a pulse of ionizing energy. Reactive ions generated by this pulse of ionizing energy mix 302 with the sample in the reaction region, producing product ions (e.g., ionized sample) and a cloud of reactive ions.

[0044] After the ionization source 104 is activated, the controller 120 waits a selected period (the first gate delay) before opening the ion shutter (304). The gate delay can include the time between the rising edge of the corona trigger and a predetermined point in the activation of the ion gate. The gate is held open for a period commonly referred to as the "gate width" before closing again. Typically, the gate width is at least 1 microsecond and may be less than 10 milliseconds. The actual gate width used can be selected based on the length of the drift chamber, the degree of sensitivity required, and the desired timing resolution. For example, for a 4 cm long drift tube, a gate width of 80 to 180 mb can be used.

[0045] Of the cloud of product and reactant ions produced by the first ionization of the sample (which may be referred to herein as first sample ions), only the portion of the ions that reach the gate during the gate width are allowed to travel through the gate toward the detector 306. More mobile ions that arrive before the shutter is opened and less mobile ions that arrive after the shutter is closed are prevented from passing through the gate (e.g., may be neutralized by the shutter).

[0046] After the shutter closes, the controller 120 then triggers the provision of power to the pulsed ionization source 104 for a second time to provide a pulse of ionization energy to further ionize (308) any sample remaining in the reaction region 102 left from the previous actuation of the ionization source 104. This produces an additional cloud of product ions and reactant ions (which may be referred to herein as second sample ions).

[0047] After the ionization source 104 is activated this second time, further ionizing the sample from which the first sample ions were derived, the controller 120 waits a selected period of time to provide a second gate delay that is different from the first gate delay before opening 310 the ion shutter. Thus, a portion of the second sample ions is selected to exit the reaction region during this second gate width, but because of the different gate delay, the ion mobility distribution of that portion of ions is different from that of the portion of the first sample ions, even though the first and second sample ions are derived from the same sample. Thus, by using a series of different gate widths, a better representation of the sample's components can be obtained.

[0048] The controller 120 may be configured to implement several refinements of the techniques described above.

[0049] As a first example, the controller 120 can be configured to use two gate delay times, with the longer delay used for the first sample ions and the shorter delay used for the second sample ions. This can help address the problem that the sample concentration in the reaction region tends to decrease over time as the sample is carried away by the drift gas or otherwise diffuses out of the reaction region. The portion of the first sample ions selected using the first (longer) gate delay can be obtained while the sample concentration in the reaction region is higher. This can improve sensitivity. Conversely, the second sample ions selected using the second (shorter) gate delay can contain relatively more reactant ions than the first sample ions. Therefore, a reactant ion peak can be obtained when the sample is depleted without losing sensitivity to the sample ions. Different gate delay sequences can be used.

[0050] As a further example, a selectable sequence of gate delays may be used. Thus, after each intake of sample into the reaction region, a series of ionization events may occur, and for each ionization event, a gate may be opened or closed, thus providing a series of ionization and gating events. In this sequence, the gate delay for each such event may be selected by the controller 120, for example, according to pre-stored data. For example, the pre-stored data may include a set of sequences adapted for the detection of a particular substance or for use in a particular situation. Different types of sequences may be used, for example: ● A sequence of increasing gate delays (as in the first example above) has shorter gate delays following earlier ionization events in the sequence, while progressively longer gate delays follow subsequent activations of the ionization device, for example, until the next intake of sample into the reaction region. • A sequence of decreasing gate delays allows longer gate delays to follow earlier ionization events in the sequence, while progressively shorter gate delays follow subsequent activations of the ionizer, for example, until the next intake of sample into the reaction region. ● A staggered (e.g., "oscillating") arrangement of gate delays, in which a medium-length gate delay follows the first ionization event in the arrangement, a shorter delay follows the next ionization event, and a longer delay (longer than the medium-length gate delay) follows each subsequent ionization event. • A combination of one or more of the above types of sequences.

[0051] Different sequences of the same type, e.g., any of the above types, may be stored, with one or more different absolute values ​​of gate delay for use in detecting a particular substance or particular situation. The controller 120 may be configured to select one or more of the stored sequences from the pre-stored data in response to user input and / or based on some sensed condition (such as temperature or humidity). As an example, the pre-stored data may include a sequence for use in calibration and a sequence for use in sampling.

[0052] Figure 3 is a schematic diagram of an example of an ion mobility spectrometer of the type shown in Figure 1. As shown, the ion mobility spectrometer shown in Figure 3 is identical to that described in Figure 1 in that it includes an ionization source 104, a reaction region 102 separated from a drift region 103 by an ion shutter 105, and a controller 120 for controlling the ion shutter and the ionization source 104. Like the IMS cell described with reference to Figure 1, the spectrometer shown in Figure 3 also includes drift electrodes 103a, 103b for providing an electric field in the drift region 103. A drift gas inlet 122 is provided in the drift region 103 near the detector 118, and a drift gas outlet 124 is provided near the shutter so that a flow of drift gas can be provided in the direction of ion movement towards the detector.

[0053] 1, the spectrometer shown in FIG. 3 may also include a pressure pulser 126. Such a pressure pulser 126 may include a transducer, such as an electromechanical transducer, arranged in the manner of a miniature loudspeaker. Such a transducer may be operable to drive a diaphragm or other means to provide a pulsed change in pressure within the reaction region 102.

[0054] 4 is a timing diagram that includes four pairs of axes: the first 400 indicates the timing of the activation of the pressure pulser, the second 402 indicates the concentration of the sample in the reaction region, the third 404 indicates the on and off switching of the pulsed ionization source 104, and the fourth 406 indicates the activation of the gate.

[0055] The timing diagram shown in FIG. 4 illustrates the operation of an ion mobility spectrometer such as that shown in FIG. 3. As shown, the pressure pulser 126 is activated 408 to draw a sample of gaseous fluid into the reaction region 102. This provides an initial sample concentration 410. The controller 120 then triggers activation of the pulsed ionization source 104 (412). This produces reactant ions, which then combine with the sample to ionize the sample and produce first sample ions. As shown, this reduces the sample concentration 414. As shown, the ion shutter 105 is held closed after the ionization source 104 is activated for a first gate delay 416. It then opens for a “gate width” period 418, allowing a portion of the first sample ions to travel toward the detector 118 before closing again. The ionizer is then activated again (420) to further ionize any sample remaining in the reaction region from the ionizer’s previous activation. As shown, this further reduces the sample concentration 422 and also produces second sample ions.

[0056] Again, the shutter is held closed after the second activation 420 of the ionization source 104 for a second gate delay 424, before being opened to move some of the second sample ions toward the detector 118. The ion shutter is then closed again, and the cycle may be repeated, for example, by activating the ionizer a third time to further ionize the remainder of the original sample, producing third sample ions that may be analyzed using a third gate delay 426. This cycle (activate ionizer, apply gate delay, open gate) may be repeated any number of times for each activation of the pressure pulser, such that each activation of the pressure pulser may be associated with a series of ion mobility data sets, each obtained using a different gate delay.

[0057] For the avoidance of doubt, the sample concentrations are shown as constant between pulses 424, 426, 428 of the ionization source 104, however, it will be understood that the sample concentrations 410, 414, 422 will generally also decrease over time as the sample diffuses from the reaction region and is carried away by the bulk flow (e.g., in the drift gas).

[0058] The methods of operation shown in Figures 2 and 4, respectively, can be further developed in various ways.

[0059] For example, the controller 120 may be configured to control the gate delay and / or gate width of the ion shutter 105 based on the ion spectrum data.

[0060] FIG. 5 shows a flowchart illustrating one such example. As shown in FIG. 3, the detector 118 of the IMS cell shown in FIG. 1 can also be connected to a controller 120. Thus, the controller 120, for example, obtains ion spectrum data from first and / or second sample ions (502). It can then determine whether peaks are present in the ion spectrum data, e.g., peaks associated with particular commodity ions and / or particular flight times. As will be understood by those skilled in the art upon reading this disclosure, such peaks can be identified in the ion spectrum data by thresholding or other methods, such as curve fitting (e.g., fitting a Gaussian). Thus, the controller 120 can obtain data indicative of the flight times of ions from the ion shutter to the detector, although other methods may be used.

[0061] The controller 120 may be configured to use such data to select a gate delay (or an array of gate delays as defined above), for example, based on the timing of one or more peaks and / or based on the detection of a particular substance or species of ion.

[0062] The arrival times determined in this manner can then be used to determine at least one gate delay for subsequent analysis of the sample or subsequent sample, for example according to the methods shown in Figure 2 or Figure 4.

[0063] By selecting the gate delay in this manner, e.g., to coincide with the expected arrival time of a particular product ion at the ion shutter, the sensitivity of the IMS instrument to a particular product ion can be increased, e.g., by increasing the amplitude of the product ion peak for a given sample concentration in the reaction region.

[0064] Figure 6 illustrates a further example of how the methods of the present disclosure may be developed. The flowchart shown in Figure 6 illustrates a method for controlling the operation of the ion shutter by decreasing the gate width during a gate delay interval associated with a product ion peak. In this method, the controller 120 determines (502) an ion spectrum and identifies (504) product ion peaks within that spectrum, as described above with reference to Figure 5. The controller 120 can then use this result to determine (506) a gate delay based on the expected time of arrival at the ion shutter of the particular product ions associated with those peaks, as also described above.

[0065] In the method shown in FIG. 6, the controller 120 can use a reduced gate width at the determined gate delay. The reduced gate width may also be used to scan a series of such gate delays. For example, the controller 120 can identify a gate delay interval based on the expected arrival time. This can be done using ion spectrum data determined using a first gate width (e.g., a default gate width for the instrument, as defined above, which may range, for example, between 1 μs and 10 ms). The controller 120 can then select a second, shorter gate width and perform a series of cycles in which the selected gate delay(s) are used and the reduced gate width is used to scan across the identified gate delay interval.

[0066] This can be done according to the method shown in Figure 4 (e.g., cycle ionizer on, apply gate delay, open gate), but with the gate width reduced and the gate delay varied with each cycle. Such a method can be particularly useful because the gate delay increases sensitivity to ions with a particular range of ion mobilities, potentially allowing more ions within that range to enter the drift region. This may allow for the use of narrower gate widths to improve timing resolution while maintaining signal-to-noise ratio. The resulting higher-resolution ion mobility spectrum data can be used to resolve ambiguities in product ion peaks.

[0067] It will be understood from the above discussion that the embodiments shown in the figures are merely exemplary and include features that may be generalized, eliminated, or substituted as described and claimed herein. Referring generally to the figures, it will be understood that schematic functional block diagrams are used to illustrate the functionality of the systems and devices described herein. However, it will be understood that functionality need not be so divided, and should not be construed to imply any particular structure of hardware other than that described and claimed below. The functionality of one or more of the elements shown in the figures may be further subdivided and / or distributed throughout the devices of the present disclosure. In some embodiments, the functionality of one or more elements shown in the figures may be combined into a single functional unit.

[0068] It will be understood in the context of the present disclosure that providing a pulse of a pulsed ionization source can include delivering electrical energy to the ionization source 120 to initiate operation of the ionization source 104. It can also include switching the ionization source off and / or returning it to a state in which ions are not generated until the next active delivery of energy to the ionization source. For example, providing a pulse of a pulsed ionization source can include both starting and stopping the supply of power to the ionization source from a power source such as a battery and / or using a switch such as a relay. The ionization sources described herein can include a corona source such as a corona point source, and in some embodiments, operation of the corona point source can include a 12 kV electrical pulse having a rise time of about 150 ns and a pulse width of 200 to 900 ns. Dielectric barrier discharge sources can also be used, in which case operation of the ionization source can include a pulse of about 10 ms duration (e.g., based on the full width at half maximum of the pulse) and a voltage of up to about 5 kV, e.g., a peak voltage in the range of 1 kV to 4.5 kV. The pulse may include an oscillatory component having a frequency characteristic of the DBD source and / or the power source to the DBD source. For example, it may include a pulse of AC voltage having a frequency of 100 Hz to 200 Hz, with a decay time of, for example, about 10 to 20 ms. The amplitude and time characteristics of the pulses generated by DBD and corona sources vary, and it will be understood that in the context of this disclosure, such pulses may include oscillatory signals modulated by a pulse envelope.

[0069] IMS cells typically use a single high-voltage power supply. For example, the maximum voltage at the top of the reaction region (the end farthest from the detector) may be resistively divided to provide the necessary voltages for each element of the IMS cell, including the electrodes that define the electric fields in the ionization and drift regions and the electrodes of the ion gate / shutter. If a corona source is used to generate ions, it may have its own dedicated power supply that provides the fixed DC and pulsed voltages that generate the ions. Instead of a high-voltage power supply, separate power supply units may be used for one or more elements of the IMS.

[0070] The above embodiments should be understood as illustrative examples. Further embodiments are envisioned.

[0071] In one embodiment, the present disclosure aims to reduce the effect of "mobility selection" described above by varying the gate delay so that product ion amplitude increases while at the same time maintaining a consistent and usable RIP. To achieve this, it is proposed to scan the gate delay through increasing values ​​during the sampling period and then perform an averaging of the resulting peak amplitudes.

[0072] In some embodiments, it may be possible to adjust the system to actively focus on the peak of interest during acquisition. For example, if the sample peak is persistent, the gate delay may be automatically adjusted to maximize that peak. With the product peak maximized as described above, another adjustment may be made: narrowing the gate pulse width, which may be useful for resolving any other peaks near the peak of interest. One such approach is described with reference to FIG. 6.

[0073] Embodiments of the present disclosure aim to improve IMS response to product ions by actively actuating the opening and closing of an ion gate. The embodiments can be implemented in any IMS system that uses a pulsed ion source, such as a corona discharge source, through software modifications. In some embodiments, no hardware modifications are required. These and other embodiments can be included in portable IMS instruments used in search scenarios. The embodiments can allow the detector to "focus" on the compound of interest and help reject false alarms.

[0074] In some examples, the functionality of controller 120 may be provided by a general-purpose processor that may be configured to perform any one of the methods described herein. In some examples, controller 120 may comprise digital logic such as a field programmable gate array, FPGA, application-specific integrated circuit, ASIC, digital signal processor, DSP, or any other suitable hardware. In some examples, one or more memory elements may store data and / or program instructions used to implement the operations described herein. Embodiments of the present disclosure provide a tangible, non-transitory storage medium comprising program instructions operable to program a processor to perform any one or more of the methods described and / or claimed herein and / or to provide a data processing apparatus described and / or claimed herein. Controller 120 may comprise analog control circuitry that provides at least a portion of its control functionality. One embodiment provides analog control circuitry configured to perform any one or more of the methods described herein.

[0075] It is to be understood that any feature described with respect to any one embodiment may be used alone or in combination with other features described, and may also be used in combination with one or more features of any other embodiment or in any combination of any other embodiment. Furthermore, equivalents and modifications not described above may also be used without departing from the scope of the invention as defined in the appended claims.

Claims

1. 1. A method of operating an ion mobility spectrometer, comprising: drawing a sample of the gaseous fluid into a reaction volume of the ion mobility spectrometer; providing a first pulse of a pulsed ionization source to ionize the sample of gaseous fluid, thereby obtaining first sample ions; opening an ion shutter after a first gate delay following a first pulse to allow a portion of the first sample ions to exit the reaction region; providing a second pulse of the pulsed ionization source after the ion shutter is closed to further ionize the sample of gaseous fluid, thereby obtaining second sample ions; opening the ion shutter after a second gate delay following a second pulse to allow a portion of the second sample ions to exit the reaction region, the second gate delay being different from the first gate delay.

2. The method of claim 1 , wherein the second gate delay is selected such that the portion of second sample ions includes reactant ions in preference to product ions.

3. The method of claim 2 , wherein the first gate delay is longer than the second gate delay.

4. 4. The method of claim 2 or 3, wherein the first gate delay is selected such that the portion of the first sample ions includes product ions in preference to reactant ions.

5. 5. The method of claim 1, further comprising obtaining ion spectral data based on analyzing at least one of the portion of first sample ions and the portion of second sample ions, and controlling subsequent operation of an ion shutter of the ion mobility spectrometer based on said analyzing.

6. 6. The method of claim 5, wherein controlling subsequent actuation of the ion shutter comprises selecting a subsequent gate delay based on a product ion peak in the ion spectrum data.

7. The method of claim 6 , wherein selecting the subsequent gate delay comprises selecting a gate delay to increase the amplitude of the product ion peak.

8. 8. The method of claim 6 or 7, wherein controlling subsequent actuation of the ion shutter comprises reducing a gate width during a gate delay interval associated with the product ion peak.

9. The method of any preceding claim, wherein at least one gate delay is selected based on the mobility of a calibrant.

10. 10. The method of claim 1, wherein the step of drawing a sample of the gaseous fluid comprises activating a pressure pulser to draw the sample into the reaction region, and wherein the first pulse of the ionization source and the second pulse of the ionization source are both performed before a next activation of the pressure pulser.

11. The method according to any one of claims 1 to 10, comprising: determining first ion spectral data based on analyzing the first sample ions; determining second ion spectral data based on analyzing the second sample ions; and combining the first ion spectral data and the second ion spectral data to provide a combined spectrum for identifying a substance of interest in the sample of gaseous fluid.

12. Detector equipment, including: a pulsed ionization source for ionizing the gaseous fluid in a reaction region of the detector instrument; Ion shutter; Controllers capable of operating: activating the pulsed ionization source to provide a first pulse that ionizes a sample of gaseous fluid in the reaction region, thereby obtaining first sample ions; controlling the ion shutter to provide a first gate delay between activating the pulsed ionization source and opening the ion shutter to allow a portion of the first sample ions to exit a reaction region; after the ion shutter is closed, activating the pulsed ionization source to provide a second pulse to further ionize the sample of gaseous fluid in the reaction region, thereby obtaining second sample ions; controlling the ion shutter to provide a second gate delay between activating the pulsed ionization source and opening the ion shutter to allow a portion of the second sample ions to exit the reaction region; wherein the second gate delay is different from the first gate delay. Detector equipment.

13. 13. The instrument of claim 12, wherein the second gate delay is selected such that the portion of the second sample ions includes reactant ions in preference to product ions.

14. The apparatus of claim 13 , wherein the first gate delay is longer than the second gate delay.

15. 15. The instrument of claim 13 or 14, wherein the first gate delay is selected so that the portion of first sample ions includes product ions in preference to reactant ions.

16. 16. The instrument of claim 13, wherein a controller is configured to obtain ion spectral data based on analysing at least one of the portion of the first sample ions and the portion of the second sample ions, and to control subsequent operation of the ion shutter based on the analysis.

17. 17. The instrument of claim 16, wherein controlling subsequent actuation of the ion shutter comprises selecting a subsequent gate delay based on a product ion peak in the ion spectrum data.

18. 18. The instrument of claim 17, wherein selecting the subsequent gate delay comprises selecting a gate delay to increase the amplitude of the product ion peak.

19. 20. The instrument of claim 17, wherein controlling subsequent actuation of the ion shutter comprises reducing a gate width during a gate delay interval associated with the product ion peak.

20. An instrument according to any one of claims 12 to 19, wherein at least one gate delay is selected based on the mobility of a calibrant.

21. a pressure pulser configured to provide a sample of gaseous fluid from an inlet of the device into the reaction region; drawing the sample of the gaseous fluid includes activating the pressure pulser to draw the sample into the reaction region, and the controller is configured such that after activating the pressure pulser, both the first pulse of the ionization source and the second pulse of the ionization source are performed before a next activation of the pressure pulser to draw the sample into the reaction region. An apparatus according to any one of claims 12 to 20.

22. 1. A method of configuring an ion mobility spectrometer, the method comprising: programming a controller of said device to carry out the method according to any one of claims 1 to 4; wherein the controller is connected to control a pulsed ionization source and an ion shutter of the device. method.

23. programming the controller to carry out a method according to any one of claims 5 to 9, the controller is coupled to a detector of the apparatus to obtain ion spectrum data; 23. The method of claim 22.

24. 24. The method of claim 22 or 23, comprising programming the controller to perform the method of claim 10, wherein the controller is connected to control a pressure pulser of the device to supply a sample of gaseous fluid into the reaction region.

25. A program comprising instructions for controlling a controller of an ion mobility spectrometer to carry out the method according to any one of claims 1 to 11 or 22 to 24.

26. 12. The method of claim 1, wherein the reaction region is separated from the drift region by an ion shutter, and opening the ion shutter allows some of the first sample ions or some of the second sample ions to leave the reaction region and enter the drift region.

27. 22. An instrument according to any one of claims 12 to 21, comprising a reaction region separated from the drift region by an ion shutter, wherein opening the ion shutter allows some of the first sample ions or some of the second sample ions to leave the reaction region and enter the drift region.

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