Ion shutter, method of controlling an ion shutter, and detection method and apparatus

Abstract

A method of operating an ion mobility spectrometer, comprising the steps of: introducing a gaseous fluid sample into a reaction region of the ion mobility spectrometer; providing a first pulse of a pulsed ionization source to ionize the gaseous fluid sample, thereby obtaining first sample ions; allowing a portion of the first sample ions to exit the reaction region after a first gate delay following the first trigger opening an ion shutter; providing a second pulse of the pulsed ionization source to further ionize the gaseous fluid sample, thereby obtaining second sample ions; allowing a portion of the second sample ions to exit the reaction region after a second gate delay following the first trigger opening the ion shutter, wherein the second gate delay is different than the first gate delay.

Description

TECHNICAL FIELD

[0001] The present invention relates to methods and apparatuses, in particular to methods and apparatuses for analyzing a substance by detecting ions, and more specifically to an ion shutter for such apparatuses and a method of controlling such an ion shutter. BACKGROUND

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

[0003] The time of flight of each ion is associated with the mobility of the ion. Ion mobility is related to its mass and geometry. Thus, by measuring the time of flight of an ion, its identity can be inferred. These time of flights can be displayed in a chart or numerically as a spectrum.

[0004] As mentioned above, some IMS units include a detector that collects ions to measure their time of flight so that they can be identified, which can be done in the presence of a drift gas so that the migration effect can separate the ions. Some IMS units can separate ions according to their time of flight so that ions with a selected time of flight (meaning a selected range of ion mobility) can be provided to other detector instruments (e.g., mass spectrometers) for further analysis. One example of this technique is known as IMS-MS, in which an IMS unit is used as an ion filter to select ions from a sample. The selected ions are then provided to a mass spectrometer. In this ion identification or filtering method, a group of ions can be released from the reaction region and / or into the inlet of the mass spectrometer by opening the ion shutter.

[0005] The reaction region of an IMS unit has a finite length, and in the time interval that the shutter remains open, ions that can be distributed around the reaction region must (at least partially) travel through the reaction region to reach the shutter.

[0006] The opening of the shutter of a pulsed ionization source IMS spectrometer is typically synchronized with the ion pulse generation. This synchronization includes a so-called “gate delay”, which occurs at a fixed time after the ion pulse has been generated. This delay is needed so that the ion pulse will be present at the shutter when it opens.

[0007] It is possible to operate the spectrometer without a shutter, or to keep the shutter continuously open. However, it has been found that the pulses generated by a gridless corona are wide and result in poor resolution. SUMMARY

[0008] Aspects and examples of the invention are set forth in the claims, and the gate delay can be varied from generally fixed to improve IMS response to materials of interest.

[0009] For example, one problem that the present disclosure can address is that the gate delay selects which ions are allowed to enter the detector from any given pulse of the ionization source. Due to migration effects in the reaction region, shorter delays tend to allow more of the smaller, more mobile ions to enter the drift region. On the other hand, longer gate delays can facilitate lower mobility ions to enter the drift region. The more mobile ions can include so-called reactant ions, while the less mobile ions can include product ions.

[0010] To address this problem of mobility selection, the gate delay can be set so that both reactant ion peaks (RIPs) and product ions are visible in a typical sample spectrum. This “compromise” setting of the gate delay can exclude some product ions from entering the drift tube. As a result, the apparent sensitivity of the detector to this type of ion will be reduced.

[0011] Embodiments of the present disclosure can aim to improve the apparent sensitivity of the IMS detector, and to reduce the above-described “mobility selection” problem.

[0012] Other problems can also be addressed by the ion shutter control techniques discussed herein.

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

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

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

[0016] Subsequent operations controlling the ion shutter may include selecting a subsequent gate delay based on the product ion peaks in the obtained ion spectral data. For example, selecting a subsequent gate delay may include selecting a gate delay to increase the amplitude of the product ion peaks, for example, by selecting a gate delay that allows a larger number of ions with that mobility range to pass through the gate. In the context of this disclosure, those skilled in the art will understand that while the precise time it takes for an ion species to travel from the ion source to the gate cannot typically be analytically defined for all systems, for any given system, a range of gate delays suitable for increasing sensitivity to ions with a particular mobility can be empirically determined.

[0017] Subsequent operations for controlling the ion shutter may include reducing the gate width during the gate delay interval associated with the product ion peak. In addition to selecting a gate delay sensitive to specific ion species that may be expected in the sample, or as an alternative to selecting a gate delay, one or more gate delays used in a sequence of such delays may be selected based on the mobility of the calibrator, for example, to enhance the calibrator peak.

[0018] Introducing a gaseous fluid sample may include operating a pressure pulser to introduce the sample into the reaction zone, wherein a first pulse and a second pulse from the ionization source are executed before the next operation of the pressure pulser.

[0019] The methods described herein may include determining first ion spectrum data based on analysis of first sample ions; determining second ion spectrum based on analysis of second sample ions; and combining the first and second ion spectrum data to provide a combined spectrum for identifying substances of interest in a gaseous fluid sample.

[0020] One aspect provides a detector comprising: a pulsed ionization source for ionizing a gaseous fluid in a reaction region of the detector instrument; an ion shutter; and a controller operable to: operate the pulsed ionization source to provide a first pulse to ionize a gaseous fluid sample in the reaction region, thereby obtaining first sample ions; control the ion shutter to provide a first gate delay between operation of the ion generator and opening of the ion shutter to allow a portion of the first sample ions to leave the reaction region; operate the pulsed ionization source to provide a second pulse to further ionize the gaseous fluid sample in the reaction region, thereby obtaining second sample ions; and control the ion shutter to provide a second gate delay between operation of the ion generator and opening of the ion shutter to allow a portion of the second sample ions to leave the reaction region; wherein the second gate delay is different from the first gate delay.

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

[0022] The at least one gate delay can be selected based on a mobility of the calibrant.

[0023] A detector described herein can include a pressure pulser (e.g., an electromechanical actuator that drives a diaphragm in the manner of a loudspeaker). Such a pressure pulser can be arranged to provide a gaseous fluid sample into a reaction region from an inlet of the instrument. Introducing the gaseous fluid sample includes operating the pressure pulser to introduce the sample into the reaction region, e.g., by providing a temporary reduction in pressure in the reaction region. The controller can be configured so that both the first pulse of the ionization source and the second pulse of the ionization source are performed before a next operation of the pressure pulser after operating the pressure pulser to introduce the sample into the reaction region.

[0024] One aspect provides a method of configuring an ion mobility spectrometry apparatus, the method comprising: programming a controller of the apparatus to perform any of the methods described or claimed herein.

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

[0026] One aspect of the present disclosure provides a computer program product, e.g., a computer readable signal or a tangible non-transitory computer readable storage medium, comprising program instructions for programming a controller of an ion mobility spectrometry apparatus to perform any of the methods described or claimed herein. Any feature of any of the examples disclosed herein can be combined with any selected features of any of the other examples described herein. For example, features of the methods can be implemented in suitably configured hardware, and configurations of particular hardware described herein can be employed in methods implemented using other hardware. Attached Figure Description

[0027] Embodiments of this disclosure will now be described in detail with reference to the accompanying drawings, in which:

[0028] Figure 1 A cross-sectional view of an ion mobility spectrometer is shown;

[0029] Figure 2 This is a flowchart illustrating the operation method of this ion mobility spectrometer;

[0030] Figure 3 It shows Figure 1 A schematic diagram of an example of an ion mobility spectrometer of the type shown;

[0031] Figure 4 This demonstrates the implementation of this ion mobility spectrometer. Figure 2 The sequence diagram of the operations of the method of the type shown;

[0032] Figure 5 It shows, for example, references Figure 2 and / or Figure 4 The flowchart explaining the operation method; and

[0033] Figure 6 This is a flowchart illustrating another such operating method of an ion mobility spectrometer.

[0034] In the accompanying drawings, the same reference numerals are used to denote the same elements.

[0035] Detailed description

[0036] Figure 1 A cross-sectional view of the ion mobility spectrometer 100 is shown.

[0037] Figure 1 The ion mobility spectrometer includes a reaction zone 102, a pulsed ionization source 104 for ionizing the gaseous fluid in the reaction zone 102, an ion shutter 105, and a controller 120.

[0038] Controller 120 is connected to ionization source 104 and shutter 105. In typical operation, whenever a sample of gaseous fluid (e.g., vapor) is provided to the reaction zone, controller 120 provides a series of pulses to ionization source 104. After each pulse, controller 120 opens ion shutter 105 after a “gate delay,” and ions generated by that pulse then travel along the drift region of the spectrometer, leaving the reaction zone and reaching the detector (e.g., a Faraday cup). Thus, each operating pulse of ionization source 104 can be used to provide an ion migration spectrum. The series of spectra generated by the series of pulses applied to each sample are then combined to provide the spectrum of that sample.

[0039] Figure 1 The controller 120 shown in is configured to vary the gate delay so that different gate delays are used for at least one of the pulses in the pulse series. Ion mobility spectra produced by combining the spectra produced using different gate delays reduce problems that might otherwise arise from "mobility selection".

[0040] An ion mobility spectrometry (IMS) cell will now be described as a whole to place the subsequent discussion of methods to address these and other problems in appropriate context.

[0041] The IMS cell comprises a housing, for example a tube 101. A reaction region 102 is at one end inside the 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 comprises an inlet 108 for enabling a sample of a gaseous fluid (for example vapour and / or gas and / or aerosol) to be introduced into the reaction region 102.

[0042] A pulsed ionisation source 104 is arranged to ionise the sample in the reaction region. In the example shown in Figure 1 In the example shown in, the pulsed ionisation source 104 comprises a corona point. The pulsed ionisation source 104 is connected so that the controller 120 can control the delivery of electrical energy to the controller 120, such as by switching on the supply of a power pulse. It will be understood in the context of the present disclosure that each operational pulse of the ionisation source 104 can comprise a period during which a series of voltage spikes are applied across the electrodes of the ionisation source 104. For example, the ionisation source 104 can have some capacitance, so that the delivery of a short DC pulse can cause some "ringing". Thus, the application of a pulse by the ionisation source 104 can comprise switching the ionisation source 104 from an "off state to an active state in which ions are generated, sometimes through a series of voltage spikes (for example, generated by an AC voltage, which can be associated with such ringing) before the source returns to the "off state.

[0043] The ion shutter 105 comprises two electrodes 106, 107, which are coupled to the controller 120 to enable a potential barrier voltage to be provided between the two electrodes 106, 107. When the shutter 105 is "closed", this potential barrier voltage serves to prevent ions from the reaction region of the IMS from travelling into the drift region, and in an open state ions can travel into the drift region towards the detector. The ion shutter 105 can comprise a Tyndall-Powell, Bradbury-Nielsen shutter or other type of shutter. The shutter electrodes 106, 107 can each comprise an elongate conductor, and the elongate conductor of the first shutter electrode 106 can be aligned with the elongate conductor of the second shutter electrode 107 in the drift direction. The elongate conductor of each shutter electrode 106, 107 can be arranged as a grid, such as a mesh, for example a triangular, rectangular, hexagonal or other regular or irregular mesh. As will be explained later, the shutter electrodes 106, 107 need not be separated in the drift direction. For example, they can be co-planar, in which case the elongate conductors can be interdigitated, for example they can be staggered or interleaved.

[0044] In Figure 1 In the example shown, the drift region 103 is located between the reaction region 102 and a detector 118, such as a collector (for example a Faraday cup for detecting arrival of ions), or another type of detector 118 such as a mass spectrometer. In the case of using such another type of detector, the inlet of this detector can be used in place of the Faraday cup, and an additional ion shutter can be inserted between the drift region and the inlet of this detector. This can be used to select (for example filter) ions provided to this other detector according to their time of flight.

[0045] A voltage profile can be provided in the drift region 103 using a series of drift electrodes 103a, 103b spaced along the drift region. Although Figure 1 Not shown in the figure, a reflectron or other electrodes can be arranged for extending this voltage profile into the reaction region 102. Between the reaction region 102 and the detector 118, the profile voltage varies spatially (for example as a function of displacement of the cell in the drift direction) to provide an electric field for moving ions along the cell 100 towards the detector 118. The electric field can be uniform and / or known along the drift region 103 and / or the reaction region 102.

[0046] The controller 120 comprises a programmable processor, an output interface such as a DAC (not shown in the figure) which is capable of controlling the provision of appropriate electrical control signals to the ion shutter and to the ionisation source 104 and / or a power supply. The controller 120 is thus operable to operate the pulsed ionisation source 104 and to control the ion shutter. The controller 120 can also store timing data indicative of gate delays associated with certain types of ion. For example, it can comprise data indicative of gate delays associated with preferentially selecting reactant ions and / or other types of ion such as calibrants.

[0047] Figure 1 The IMS cell 100 shown in the figure can also comprise a drift gas inlet 122 into the drift region near the detector and a drift gas outlet near the shutter, so that a flow of (clean, dry) drift gas can be provided against the direction in which the ions travel towards the detector.

[0048] Reference will now be made to Figure 2 the operation of the IMS cell 100 shown in the figure. Figure 1

[0049] In operation, a gaseous fluid sample such as a vapour is provided 300 into the reaction region 102. The controller 120 then triggers the provision of electrical power to the pulsed ionisation source 104, which provides a pulse of ionisation energy. The reactant ions produced by the pulse of ionisation energy mix 302 with the sample in the reaction region to produce a cloud of product ions (e.g. the ionised sample) and reactant ions.

[0050] After the ionisation source 104 has been operated, the controller 120 waits for a selected period of time before opening 304 the ion shutter (a first gate delay). The gate delay can comprise the time between the rising edge of the corona trigger and a predetermined point in the operation of the ion gate. The gate remains open for a period of time before being closed again, often referred to as the “gate width”. Typically, the gate width is at least a microsecond, and can be less than 10ms. The gate width actually used can be selected based on the length of the drift chamber, the sensitivity required and the timing resolution desired. For example, for a drift tube of 4cm in length, a gate width of between 80 and 180μb can be used.

[0051] Of the cloud of product ions and reactant ions produced by the first ionisation of the sample (which can be referred to herein as the first sample ions), only the portion of the ions which reach the gate during the gate width are allowed to travel 306 towards the detector through the gate. The more mobile ions which reach the gate before the shutter opens, and the fewer mobile ions which reach the gate after the shutter closes, the fewer mobile ions are prevented from passing through the gate (e.g. they can be neutralised at the shutter).

[0052] ​After the shutter has closed, the controller 120 then triggers a second pulse of power to the pulsed ionisation source 104, which provides a pulse of ionisation energy to further ionise 308 the sample remaining in the reaction region 102, which is left over from the previous operation of the ionisation source 104. This produces a further cloud of product ions and reactant ions (which can be referred to here as a second sample ion).

[0053] After the second operation of the ionisation source 104 to further ionise the sample from which the first sample ions were derived, the controller 120 then waits for a selected period of time before opening 310 the ion shutter to provide a second gate delay which is different from the first gate delay. Thus, a portion of the second sample ions is selected to exit the reaction region during this second gate width, but due to the different gate delay, even though the first sample ions and the second sample ions are from the same sample, the distribution of ion mobilities in said portion of the second sample ions will be different from the distribution of ion mobilities of the portion of the first sample ions. Thus, by using a series of different gate widths, a better representation of the composition of the sample can be obtained.

[0054] The controller 120 can be configured to implement a number of refinements to the above described method.

[0055] As a first example, the controller 120 can be configured so that in the two gate delay times, the longer delay is used for the first sample ions and the shorter delay is used for the second sample ions. This can help to address the problem that the concentration of sample 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 concentration of sample in the reaction region is higher. This can improve sensitivity. Conversely, the second sample ions selected using the second (shorter) gate delay can include relatively more reactant ions than the first sample ions. Thus, when the sample has been depleted, a reactant ion peak can be obtained without losing sensitivity to the sample ions. Different sequences of gate delays can be used.

[0056] As a further example, a selectable sequence of gate delays can be used. Thus, after each introduction of sample into the reaction region, a series of ionisation events can occur, and for each ionisation event, the gate can be opened and closed, providing a series of ionisation & gating events. The gate delay for each such event in the sequence can be selected by the controller 120, for example from pre-stored data. For example, the pre-stored data can include a set of sequences; each sequence is suitable for detecting a particular substance or for a particular environment. Different types of sequence can be used, for example:

[0057] • a sequence of increasing gate delays (as in the first example described above), such that shorter gate delays follow earlier ionisation events in the sequence, and progressively longer gate delays follow subsequent operation of the ion generator, e.g. until the next sample is introduced into the reaction region.

[0058] • a sequence of decreasing gate delays, such that longer gate delays follow earlier ionisation events in the sequence, and progressively shorter gate delays follow subsequent operation of the ion generator, e.g. until the next sample is introduced into the reaction region.

[0059] • an interleaved (e.g. "oscillating") sequence of gate delays, in which an intermediate length gate delay follows the first ionisation event in the sequence, and a shorter delay follows the next ionisation event, and a longer delay (longer than the intermediate length gate delay) follows the subsequent ionisation event.

[0060] • a combination of one or more of the preceding types of sequence.

[0061] Different sequences of the same type, e.g. of any of the types described above, and having one or more different absolute values of gate delay, can also be stored for use in detecting particular substances or in particular circumstances. The controller 120 can 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 (e.g. temperature or humidity). As one example, the pre-stored data can include a sequence for calibration and a sequence for sampling.

[0062] Figure 3 is Figure 1 a schematic diagram of an example of an ion mobility spectrometer of the type shown. As shown, Figure 3 the ion mobility spectrometer shown is the same as Figure 1 the ion mobility spectrometer described in relation to Figure 1 the IMS unit described in relation to Figure 3 the spectrometer shown in also includes drift electrodes 103a, 103b for providing an electric field in the drift region 103. A drift gas inlet 122 is provided into the drift region 103 near the detector 118, and a drift gas outlet 124 is provided near the shutter, such that a flow of drift gas can be provided against the direction in which ions travel towards the detector.

[0063] In addition to the features described in relation to Figure 1 the IMS unit described in relation to Figure 3The spectrometer shown may also include a pressure pulser 126. This pressure pulser 126 may include a transducer, such as an electromechanical transducer arranged in the manner of a miniature loudspeaker. This transducer may be operable to drive a diaphragm or other device to provide pulsed pressure changes in the reaction zone 102.

[0064] Figure 4 It is a timing diagram including 4 pairs of axes. The first 400 shows the operating timing of the pressure pulser, the second 402 shows the sample concentration in the reaction zone, the third 404 shows the opening and closing of the pulsed ionization source 104, and the fourth 406 shows the operation of the gate.

[0065] Figure 4 The timing diagram shown illustrates, for example, Figure 3 The operation of the ion mobility spectrometer is illustrated. As shown, pressure pulser 126 is operated 408 to introduce a gaseous fluid sample into reaction zone 102. This provides an initial sample concentration 410. Controller 120 then triggers operation 412 of pulsed ionization source 104. This generates reactant ions, which then bind to the sample to ionize it, thus generating first sample ions. As shown, this reduces the sample concentration 414. As shown, after the ionization source 104 has been operated with a first gate delay 416, the ion shutter 105 remains closed. Then, during a "gate width" period 418, the ion shutter 105 is opened to allow a portion of the first sample ions to travel toward detector 118 before closing again. The ion generator is then operated again 420 to further ionize the sample retained in the reaction zone by the previous operation of the ion generator. As shown, this further reduces the sample concentration 422 and also generates second sample ions.

[0066] Furthermore, after the second operation 420 of the ionization source 104, the shutter remains closed within the second gate delay 424 before it is opened to allow a portion of the second sample ions to travel toward the detector 118. The ion shutter is then closed again, and this cycle can be repeated, for example by operating the ion generator a third time to further ionize the residue of the original sample, generating a third sample ion that can be analyzed using the third gate delay 426. For each operation of the pressure pulser, this cycle (operating the ion generator, applying the gate delay, opening the gate) can be repeated an arbitrary number of times, such that each operation of the pressure pulser can be associated with a series of ion mobility datasets, each obtained using a different gate delay.

[0067] For the avoidance of doubt, although the sample concentration is shown as being constant between pulses 424, 426, 428 of the ionisation source 104, it will be appreciated that the sample concentration 410, 414, 422 also generally decreases over time as the sample diffuses out of the reaction region and is carried away by the bulk flow (e.g. in the drift gas).

[0068] Figure 2 and Figure 4 The methods of operation shown in

[0069] For example, the controller 120 can be configured to control the gate delay and / or gate width of the ion shutter 105 based on ion spectral data.

[0070] Figure 5 A flowchart illustrating one such example is shown. As shown, at Figure 3 in Figure 1 The detector 118 of the IMS unit shown in may also be connected to the controller 120. The controller 120 may, for example, therefore obtain 502 ion spectral data from the first sample ions and / or the second sample ions. It can then determine whether there are peaks in the ion spectral data, for example peaks associated with particular product ions and / or particular times of flight. As will be appreciated by the skilled reader of the present disclosure, such peaks can be identified in the ion spectral data by thresholding or other methods such as curve fitting (e.g. fitting Gaussians). The controller 120 may, therefore, obtain data indicative of the time of flight of ions from the ion shutter to the detector, but other methods can be used.

[0071] The controller 120 can be configured to use such data to select a gate delay (or sequence 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 ion species.

[0072] The arrival time thus determined can then be used to determine at least one gate delay for subsequent analysis of the sample or a subsequent sample, for example according to the method shown in Figure 2 or Figure 4 The controller 120 can be configured to use such data to select a gate delay (or sequence 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 ion species.

[0073] Selecting the gate delay in this way, for example to match the expected time of arrival of a particular product ion at the ion shutter, can increase the sensitivity of the IMS device to those particular product ions, for example by increasing the amplitude of the product ion peak for a given sample concentration in the reaction region.

[0074] Figure 6 Another example of the way in which the methods of the present disclosure can be developed is shown. Figure 6The flowchart shown illustrates a method for controlling the operation of an ion shutter by reducing the gate width during the gate delay interval associated with the product ion peak. In this method, controller 120 determines ion spectrum 502 and identifies product ion peaks in spectrum 504, as described above. Figure 5 As explained above, the controller 120 can use this data to determine the 506 gate delay based on the expected time for the specific product ions associated with those peaks to reach the ion shutter.

[0075] exist Figure 6 In the method shown, the controller 120 can then use a reduced gate width at the determined gate delay. It can also use the reduced gate width to scan a series of such gate delays. For example, the controller 120 can identify the 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., the default gate width for the instrument, which can be in a range defined, for example, between 10 μs and 10 ms, as described above). The controller 120 can then select a second, shorter gate width and perform a series of loops in which the identified gate delay interval is scanned using one or more selected gate delays and the reduced gate width.

[0076] This can be based on Figure 4 The method illustrated (e.g., operating the ion generator, applying a gate delay, and looping the gate open) accomplishes this, but with a reduced gate width, and the gate delay can be varied in each loop. Such a method can be particularly useful because the gate delay can increase sensitivity to ions with a specific range of ion mobilities, allowing more ions within that range to enter the drift region. This, in turn, allows for the use of a narrower gate width to improve temporal resolution while maintaining the signal-to-noise ratio. The resulting higher-resolution ion mobility spectrometry data can be used to resolve ambiguities in product ion peaks.

[0077] From the foregoing discussion, it will be understood that the embodiments shown in the figures are merely exemplary and include features that can be generalized, removed, or replaced as described herein and in the claims. Referring generally to the accompanying drawings, it will be understood that the schematic functional block diagrams are used to indicate the functionality of the systems and devices described herein. However, it will be understood that functionality need not be divided in this way and should not be construed as implying any particular hardware architecture other than the hardware described and claimed below. The functionality of one or more elements shown in the figures may be further subdivided and / or distributed throughout the device of this disclosure. In some embodiments, the functionality of one or more elements shown in the figures may be integrated into a single functional unit.

[0078] It will be understood in the context of the present disclosure that providing a pulse to the 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 turning off the ionization source, and / or allowing it to return to a state in which it does not produce ions until the next time energy is actively delivered to the ionization source. For example, providing a pulse to the pulsed ionization source can include initiating and ending the supply of electrical 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, in some examples operation of the corona point source can include an electrical pulse of 12 kV with a rise time of about 150 ns and a pulse width of between 200 ns and 900 ns. A dielectric barrier discharge source can also be used, in which case operation of the ionization source can include a pulse of about 10 ms in duration (e.g. based on the full width at half maximum of the pulse), and can include a voltage of up to about 5 kV (e.g. a peak voltage in the range lkV to 4.5 kV). The pulse can include an oscillatory component with the frequency characteristic of the power supply to the DBD source and / or of the DBD source. For example, it can include an alternating voltage pulse with a frequency between 100 Hz and 200 Hz, for example with a decay time of about 10 to 20 ms. The amplitude and temporal characteristics of the pulses produced by DBD and corona sources can vary, but it will be understood in the context of the present disclosure that such pulses can include an oscillatory signal modulated by a pulse envelope.

[0079] The IMS cell typically employs a single high voltage power supply. The maximum voltage at the top of the reaction region (the end furthest from the detector) can be resistively divided to provide the voltage required for each element of the IMS cell, including the electrodes defining the electric fields of the ionization and drift regions and the electrodes of the ion gates / shutters. In the case where a corona source is used to generate ions, it can have its own dedicated power supply which provides a fixed DC voltage and the pulsed voltage to generate ions. Instead of a high voltage power supply, a separate power supply unit can be used for one or more elements of the IMS.

[0080] The above-described embodiments are to be understood as illustrative examples. Further embodiments can be envisaged.

[0081] In one embodiment, the object of the present disclosure is to reduce the impact of the above-described "mobility selection" by changing the gate delay so that the product ion amplitude increases, but at the same time the consistent and usable RIP is maintained. To achieve this, it is proposed to scan the gate delay by increasing the value during the sampling period and then perform an average of the resulting peak amplitudes.

[0082] In embodiments, the system can be actively tuned during acquisition to focus on peaks of interest. For example, if a sample peak is persistent, the gate delay can be automatically adjusted to maximize that peak. In the case of maximizing a product peak as described above, another adjustment can be performed, namely, to make the gate pulse width narrower, which can be used to resolve any other peaks that are located near the peak of interest. Referring to Figure 6 A method is described that does this.

[0083] Embodiments of the present invention aim to improve IMS response to product ions by active manipulation of the opening and closing of the ion gate. 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 changes will be required. These and other embodiments can be included in portable IMS equipment for search situations. Embodiments can help enable the detector to "focus" on a compound of interest, and help reject false alarms.

[0084] In some examples, the functionality of the controller 120 can be provided by a general purpose processor, which can be configured to perform a method in accordance with any of those described herein. In some examples, the controller 120 can comprise digital logic, such as a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a (digital signal processor) DSP, or any other appropriate hardware. In some examples, one or more memory elements can store data and / or program instructions for implementing 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 as described and / or claimed herein. The controller 120 can comprise an analog control circuit providing at least a portion of this control functionality. Embodiments provide an analog control circuit configured to perform any one or more of the methods described herein.

[0085] It will be appreciated that any features described in relation to any one embodiment can be used individually or in combination with other features described, and also in combination with one or more features of any other embodiment, or any combination of any other embodiment. Furthermore, equivalents and modifications not described above can also be employed without departing from the scope of the application as defined in the appended claims.

Claims

1. A method of operating an ion mobility spectrometer comprising a pulsed ionization source, a reaction region separated from a drift region by an ion shutter, the method comprising: introducing a gaseous fluid sample into the reaction region of the ion mobility spectrometer; providing a first pulse of the pulsed ionization source to ionize the gaseous fluid sample, thereby obtaining first sample ions; opening the ion shutter to allow a portion of the first sample ions to exit the reaction region and enter the drift region after a first gate delay following the first pulse; providing a second pulse of the pulsed ionization source to further ionize the gaseous fluid sample, thereby obtaining second sample ions; opening the ion shutter to allow a portion of the second sample ions to exit the reaction region and enter the drift region after a second gate delay following the second pulse, wherein the second gate delay is different than the first gate delay.

2. The method of claim 1, wherein the second gate delay is selected so 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. The method of claim 2 or 3, wherein the first gate delay is selected so that the portion of first sample ions includes product ions in preference to reactant ions.

5. The method of any of claims 1-3, 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 a subsequent operation of the ion shutter of the ion mobility spectrometer based on the analysis.

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

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

8. The method of claim 5, wherein controlling the subsequent operation of the ion shutter comprises reducing a gate width during a gate delay interval associated with a product ion peak.

9. The method of any of claims 1-3, wherein at least one gate delay is selected based on a mobility of a calibrant.

10. The method of any of claims 1-3, wherein introducing the gaseous fluid sample comprises operating a pressure pulser to introduce the sample into the reaction region, wherein both the first pulse of the ionization source and the second pulse of the ionization source are performed prior to a next operation of the pressure pulser.

11. The method of any of claims 1-3, 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 gaseous fluid sample.

12. A detector instrument, comprising: ​ a pulsed ionisation source for ionising a gaseous fluid in a reaction region of the detector instrument; an ion shutter; a reaction region separated from a drift region by the ion shutter; and a controller operable to: operate the pulsed ionisation source to provide a first pulse to ionise a gaseous fluid sample in the reaction region, thereby obtaining first sample ions; control the ion shutter to provide a first gate delay between operation of the pulsed ionisation source and opening of the ion shutter to allow a portion of the first sample ions to exit the reaction region and enter the drift region; operate the pulsed ionisation source to provide a second pulse to further ionise the gaseous fluid sample in the reaction region, thereby obtaining second sample ions; and control the ion shutter to provide a second gate delay between the operation of the pulsed ionisation source and opening of the ion shutter to allow a portion of the second sample ions to exit the reaction region and enter the drift region, wherein the second gate delay is different to the first gate delay.

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

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

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

16. The instrument of any one of claims 13 to 14, wherein the controller is configured to obtain ion spectral data based on analysis of at least one of the portion of first sample ions and the portion of second sample ions, and to control a subsequent operation of the ion shutter based on the analysis.

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

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

19. The instrument of claim 16, wherein controlling a subsequent operation of the ion shutter comprises reducing a gate width during a gate delay interval associated with a product ion peak.

20. The instrument of any one of claims 12 to 14, wherein at least one gate delay is selected based on a mobility of a calibrant.

21. The instrument of any one of claims 12 to 14, comprising a pressure pulser arranged to provide a gaseous fluid sample from an inlet of the instrument into the reaction region, wherein introducing the gaseous fluid sample comprises operating the pressure pulser to introduce the sample into the reaction region, and the controller is configured such that both the first pulse of the ionization source and the second pulse of the ionization source are performed prior to a next operation of the pressure pulser after operating the pressure pulser to introduce the sample into the reaction region.

22. A method of configuring an ion mobility spectrometry apparatus, the method comprising: programming a controller of the apparatus to perform the method of any of claims 1 to 4, wherein the controller is connected for controlling a pulsed ionization source and an ion shutter of the apparatus.

23. The method of claim 22, comprising programming the controller to perform the method of any of claims 5 to 9, wherein the controller is coupled to a detector of the apparatus for obtaining ion spectral data.

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

25. A computer program product comprising program instructions for programming a controller of an ion mobility spectrometry apparatus thereby to perform the method of any of claims 1 to 11 or 22 to 24.

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