Method and apparatus for improving false alarm rate in tracking detection

Abstract

One aspect of the present disclosure provides a spectrometer for detecting a substance of interest, the spectrometer comprising: a chamber through which a plurality of sample ions travel from an ion gate to a collector electrode; a detector connected to the collector electrode for detecting the arrival of sample ions to the collector electrode; a controller configured to: control parameters of the spectrometer to selectively increase or decrease the number of sample ions entering the chamber each time the ion gate is opened, detect the sample ions reaching the collector electrode during a set of time windows after opening the ion gate to obtain a detection signal, the detection signal in the time window is analyzed based on the parameters of the spectrometer to detect the presence of the substance of interest.

Description

Technical Field

[0001] The present invention relates to methods and devices, and more particularly to methods and devices for analyzing substances by detecting ions, and more specifically to methods for adjusting the analysis applied to spectral signals according to parameters of a spectrometer. Background Art

[0002] An ion mobility spectrometer (IMS) can identify materials from a sample of interest by ionizing the material (e.g., molecule, atom, etc.) and measuring the time it takes the resulting ions to travel a known distance through a countercurrent of a drift gas under a known electric field. Typically, this time is measured from the time the ion gate (which may also be referred to as an ion gate) is opened to the time the ions reach a detector such as a Faraday cup.

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

[0004] Some IMS units include detectors that collect ions to measure their flight time 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. Other types of detectors can use the travel time through the chamber under an electric field to measure the mass-to-charge ratio without a drift gas. Such a device can be called a time-of-flight mass spectrometer (TOF-MS). These and other technologies are widely used in the detection of chemicals. One of the basic characteristics of a detector is its sensitivity. Sensitivity is a way of indicating the minimum detectable concentration of a substance of interest. Sensitivity is strongly related to the false alarm rate (FAR) of the instrument, and an increase in sensitivity usually corresponds to an increase in FAR.

[0005] SUMMARY OF THE DISCLOSURE

[0006] The present disclosure aims to provide improved sensitivity and improved false alarm rates.

[0007] Aspects and embodiments of the invention are set out in the accompanying claims.

[0008] In one aspect, a spectrometer for identifying the presence of a substance of interest is provided, the spectrometer comprising: a chamber through which a plurality of sample ions travel from an ion gate to a collector electrode; a detector connected to the collector electrode for detecting the arrival of the sample ions at the collector electrode; and a controller configured to: control parameters of the spectrometer to selectively increase or decrease the number of sample ions entering the chamber each time the ion gate is opened, detect the arrival of the sample ions at the collector electrode to obtain a detection signal during a set of time windows after the ion gate is opened, and analyze the detection signal in the time window according to the parameters of the spectrometer to identify the presence of the substance of interest.

[0009] The parameters may include at least one of the following:

[0010] (i) Gate width,

[0011] (ii) the amount of sample vapor introduced into the reaction zone including the ionizer, and

[0012] (iii) The duration that the ions remain in the reaction zone before the ion gate is turned on.

[0013] While any one or more of these parameters may be used to increase or decrease the number of sample ions entering the chamber each time the ion gate is opened, it is believed that the gate width may be most effective in a typical IMS system.

[0014] Analyzing the detection signal according to parameters may include:

[0015] selecting at least one detection criterion based on the parameter, and

[0016] The presence of the substance of interest is identified based on the detection signal and the at least one detection criterion.

[0017] For example, the detection criteria may include a detection threshold in a specific time window, or a signature associated with a substance of interest. Such a signature includes an expected peak shape, and the controller may be configured to detect the peak shape, which may be done based on any appropriate curve matching or fitting algorithm.

[0018] The marker may include the presence of a monomer peak and / or a dimer peak associated with the substance of interest. For example, a specific substance may be detected based on only its monomer peak or only its dimer peak, or based on the presence of a monomer peak at one gate width and a dimer peak at a different gate width.

[0019] The controller may be configured to select time windows according to a parameter and to deactivate some of the time windows when a particular gate width is used. For example, time windows associated with known interferers may be deactivated.

[0020] The controller can be configured to:

[0021] operating the spectrometer with a first parameter to obtain a first detection signal and applying a first detection criterion to the first detection signal, and then

[0022] The spectrometer is operated with second parameters to obtain a second detection signal and a second detection criterion is applied to the second detection signal, wherein the second detection criterion is different from the first detection criterion.

[0023] The first detection criterion may include at least one of: (a) a first detection threshold for the time window, (b) one or more expected peak shapes for the time window; (c) activating or deactivating the selected time window.

[0024] In one aspect, a method for controlling a spectrometer is provided, the spectrometer comprising:

[0025] a chamber through which sample ions travel from an ion gate to a collector electrode, wherein the spectrometer is configured to differentiate ions based on their travel time to the collector electrode;

[0026] a detector connected to the collector electrode for detecting the arrival of sample ions at the collector electrode;

[0027] The method includes:

[0028] operating the spectrometer according to a first parameter and detecting the arrival of the sample ions at the collector electrode to obtain a first detection signal associated with the first parameter, operating the spectrometer according to a second parameter and detecting the arrival of the sample ions at the collector electrode to obtain a second detection signal associated with the second parameter, wherein the first parameter is different from the second parameter,

[0029] wherein the detection signal comprises detecting the arrival of ions during a set of time windows after the ion gate is turned on,

[0030] The method further includes analyzing the first detection signal according to a first detection criterion and analyzing the second detection signal according to a second detection criterion, wherein the first detection criterion is different from the second detection criterion.

[0031] As described above, the parameters typically include at least one of: gate width, (ii) the amount of sample vapor introduced into a reaction region including the ionizer, and (iii) the duration that ions remain in the reaction region before the ion gate is turned on.

[0032] Embodiments of the present disclosure provide a computer program product and a controller configured to control a spectrometer to perform any one or more of the methods described herein. Typically, the control logic is connected to the detector and the ion gate of the mass spectrometer.

[0033] Embodiments vary the gate width (open time of the ion gate) between operations of the detector, such that the detector can be operated with one gate width and then with a different gate width. The change in gate width provides a consequent change in instrument sensitivity. A different detection algorithm can be used for each of the two gate widths. Other methods of adjusting sensitivity can also be used

[0034] Embodiments relate to dynamic adjustment of the ion gate open time (gate width) and the detection algorithm used. These embodiments may be used in IMS.

[0035] Embodiments may have the advantage that a single detector may be employed to detect a very wide range of concentrations of different chemical hazards without requiring the user to change the operating configuration.

[0036] Embodiments may also have the advantage that adjustment of the detection algorithm allows for increasing the dynamic range response of the detector for a given chemical hazard and / or providing increased sensitivity to a chemical hazard while controlling or avoiding sensitivity to interferents.

[0037] 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, comprising program instructions for programming a controller of an ion mobility spectrometry apparatus to perform any of the methods described or claimed herein.

[0038] Any feature of any one of the examples disclosed herein may be combined with any selected feature of any one of the other examples described herein. For example, the features of the method may be implemented with appropriately configured hardware, and the configuration of specific hardware described herein may be adopted in the method implemented using other hardware. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings, in which:

[0040] Figure 1 shows a cross-sectional view of an ion mobility spectrometer;

[0041] Figure 2is a schematic diagram indicating detection windows such as those employed in the methods and apparatus described herein;

[0042] Figure 3 is a graph of two detection signals, such as those obtained using two specific gate widths in the presence of a first specific chemical;

[0043] Figure 4 is a graph of two detection signal graphs, such as those obtained using two specific gate widths in the presence of a second specific chemical

[0044] Figure 5 It shows that Figure 1 A flow chart showing the operating modes of the spectrometer shown; and

[0045] Figure 6 Is the description Figure 1 FIG. 1 is a flow chart of an operating mode of a spectrometer shown in FIG. 1 , wherein like reference numerals are used to denote like elements in the drawings.

[0046] Specific description

[0047] Figure 1 The ion mobility spectrometer includes a reaction region 102 , an ion source 104 for ionizing a gaseous fluid in the reaction region 102 , an ion gate fast grid 105 , a collector electrode 118 (eg, a Faraday cup), and a controller 120 .

[0048] The controller 120 is connected to the ion gate fast gate 105 and the collector electrode for sensing the arrival of ions at the collector electrode. The controller may also be connected to operate the ion source 104. In typical operation, the controller 120 provides a pulse or pulse train of the ion source 104 whenever a sample of a gaseous fluid (e.g., steam) is provided to the reaction zone. After each pulse, the controller 120 opens the ion fast gate 105 after a "gate delay", and the length of time that the fast gate 105 remains open is referred to as the "gate width" or gate open time, which is different from the gate delay.

[0049] During the gate width, ions generated in the reaction zone 102 travel along the drift region 103 of the spectrometer to leave the reaction zone 102 and reach the collector electrode. The number of ions entering the drift region through the gate depends on the gate width. A longer gate width means more ions, resulting in a higher ion current at the collector electrode. Conversely, a shorter gate width means fewer ions and a lower ion current. The sample ions are then detected at the collector electrode during a set of time windows after the ion gate is turned on to obtain a detection signal.

[0050] The spectrometer comprises a housing, such as a tube 101. A reaction region 102 is at one end inside the housing 101 and is separated from a collector electrode 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 (e.g., vapor and / or gas and / or aerosol) to be introduced into the reaction region 102.

[0051] The ion fast gate 105 includes two electrodes 106, 107, which are coupled to the controller 120 so that a barrier voltage can be provided between the two electrodes 106, 107. When the fast gate 105 is "closed", the barrier voltage is used to prevent ions from moving from the reaction region of the IMS into the drift region, and in the open state, ions can move toward the detector into the drift region. The ion fast gate 105 may include a Tyndall-Powell, Bradbury-Nielsen fast gate or other types of fast gates. The fast gate electrodes 106, 107 may each include an elongated conductor, and the elongated conductor of the first fast gate electrode 106 may be aligned with the elongated conductor of the second fast gate electrode 107 in the drift direction. The elongated conductors of each fast gate electrode 106, 107 can be arranged as a grid, such as a mesh structure, for example, a triangular, rectangular, hexagonal or other regular or irregular mesh structure. The fast gate electrodes 106, 107 do not need to be separated in the drift direction. For example, they may be coplanar, in which case the elongate conductors may be interdigitated, for example, they may be interwoven or braided.

[0052] The ionization source 104 is arranged to ionize the sample in the reaction region. Figure 1 In the example shown, the ionization source 104 comprises a corona point. The ionization 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 a supply of electrical pulses.

[0053] A voltage distribution may be provided in the drift region 103 using a series of drift electrodes 103a, 103b spaced apart along the drift region. Figure 1 Not shown, reflective plates or other electrodes may be arranged to extend the voltage distribution into the reaction region 102. Between the reaction region 102 and the detector 118, the distributed voltage varies spatially (e.g., as a function of the displacement of the cell along 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.

[0054] The controller 120 includes a programmable processor, an output interface such as a DAC (not shown in the figure), which can control the provision of appropriate electrical control signals and / or power to the ion fast grid and to the ion source 104. The controller 120 is therefore operable to operate the pulsed ionization source 104 and control the ion fast grid. Typically, in operation, the controller operates the pressure pulser to provide a sample of the material into the reaction zone. Then, it provides a series of operating cycles. During each cycle, the ionizer can be operated to ionize the sample. In each operating cycle, the gate is opened to allow ions to travel toward the collector, thereby providing a detection signal at the collector electrode.

[0055] The controller 120 can store preconfigured gate width values ​​and corresponding detection criteria associated with these gate widths. For example, the controller is configured so that detection signals of one gate width are analyzed differently from those associated with a second different gate width. Various different analyses are possible. As a first example, for detection signals associated with a shorter gate width, the detection threshold in a selected time window can be relatively low. In contrast, for a second detection signal obtained using a longer gate width, the thresholds in those time windows can be higher and / or certain time windows can be completely ignored. The controller is also configured to perform specific actions based on the combined results of one or two or more such analyses, such as triggering an alarm indicating the presence of a specific chemical hazard.

[0056] Figure 2 Schematic diagram of a set of time windows 500, 502, 504, 506, 508, 512. As shown, each of these time windows corresponds to a time interval (drift time) to the collector. Such time intervals are usually measured from the operation (opening) of the gate. The detection signal during each time window can be based on the amplitude of the ion current during the time window.

[0057] Figure 3Two curves 606, 608 on a pair of axes are shown. The x-axis 604 represents the drift time and the y-axis represents the ion current measured at the detector. Both axes are unitless because the data is merely illustrative, but the scaling applied to the two figures is equivalent for ease of comparison. The first curve 606 indicates the ion current measured at the collector electrode using the first gate width. The second curve 608 indicates the ion current measured at the collector of the same sample using the second gate width. The second gate width is longer than the first gate width. It can be seen that in both figures, the monomer peaks associated with the chemicals in the sample are clearly detectable. However, the dimer peak is relatively low in the short gate width data. For some chemicals, the monomer peak may overlap with the interferent chemical, so detecting the monomer peak alone may not be enough to clearly identify the presence of such chemicals. Therefore, it may be necessary to detect the dimer peak. In order to handle this possibility, the controller can be configured to switch to using a longer gate width when a detection threshold is reached in the time window associated with the monomer peak when using a shorter gate width. When analyzing detection signals collected using longer gate widths, detection criteria used by the controller may include deactivating (eg, ignoring) time windows associated with monomer peaks and / or windows(es) associated with known interferents.

[0058] Figure 4 Two curves 706, 708 are shown on a pair of axes 700. The x-axis 604' indicates the drift time and the y-axis 602' indicates the ion current measured at the detector. Both axes are unitless because the data is merely illustrative, but the scaling applied to the two figures is equivalent for ease of comparison. The first curve 706 indicates the ion current measured at the collector electrode using a first gate width. The second curve 708 indicates the ion current measured at the collector of the same sample using a second gate width. The second gate width is longer than the first gate width. It can be seen that when the first gate width is used, the monomer peak may not be reliably distinguished from the background signal. Therefore, the controller can be configured so that in the event that the detection threshold is not met, the gate width is increased and a corresponding increase in the detection threshold is also provided in the relevant time window.

[0059] As can be appreciated from the foregoing discussion, the controller is configured to select an analysis to be used in each time window based on the width of the gate. Preconfiguration for detecting a particular chemical threat may be performed in this manner such that a particular sequence of gate widths and corresponding detection criteria are preconfigured for detecting a particular chemical. For example, in a first analysis, the controller may use a first set of detection thresholds in a time window, selecting thresholds in a particular time window based on the prevalence of a particular known interferent and based on the signature of the chemical hazard(s) to be detected.

[0060] The controller can then employ a sequence of gate widths and corresponding detection thresholds. These sequences can be provided in a variety of ways. This will now be explained with reference to two different embodiments of the method of operating the spectrometer. In summary, the two embodiments are:

[0061] Automatic switching between gate width and detection logic settings.

[0062] Conditional switching of gate width and detection logic, such as switching of gate width and detection logic if a particular chemical hazard is not detected using a default gate width.

[0063] like Figure 5 As shown, in the first of these embodiments, the controller is configured to switch between using a default gate width and using a first analysis in a corresponding time window, and automatically switch to a different gate width and a corresponding different analysis. The controller sets the gate width to a first value (e.g., the default gate width), and operates the pressure pulse generator to obtain 300 a material sample in the reaction zone, and operates the ionizer to produce ions that ionize the sample 302 in the reaction zone. Then, the controller operates 304 the gate using the first gate width, and selects a corresponding analysis based on the gate width. Then, the controller detects the arrival of ions at the collector electrode to generate a detection signal, such as an ion flow associated with the arrival of ions at the collector. The controller analyzes 306 the detection signal in a set of time windows according to the selected analysis. Then, the controller automatically switches to using a second different gate width and uses a corresponding second analysis. For example, it can further ionize 308 the sample in the reaction zone, then operate 310 the gate using the second gate width before detecting ions, and analyze 312 the detection signal using the second analysis. The controller can be configured to determine whether a chemical hazard exists based on the results of the first analysis and / or the second analysis. For example, the two results can be used together to determine whether a chemical hazard exists, such as to trigger an alarm.

[0064] The second analysis can be selected according to the second gate width. The controller can be configured to switch from the first gate width to the second gate width after a selected number of cycles of operation with the first gate width or after a selected time interval. There may be a certain degree of conditionality in such a system. For example, in the case where a chemical hazard is detected in either of the two configurations, the controller may be configured to perform a repeated operation cycle in the configuration. This can be done until a predetermined maximum amplitude threshold is reached. Once the threshold is reached, if the controller is in the second configuration, it can be restored to the original configuration (first gate width, first analysis) to avoid saturation of the instrument. Similarly, in the case where no chemical hazard is detected using the default gate width, the operation of the controller simply continues and automatically switches to using a second different gate width and a second analysis in the time window. Then, if no hazard is detected, the controller then automatically restores to the first configuration. It will be understood in the context of the present disclosure that more than two different configurations can be used in this sequence, so that the controller automatically switches between three or more different gate widths and applies corresponding different analyses to the detection signals obtained at each different gate width.

[0065] Figure 6 A second of the above-described embodiments is shown. In this embodiment, the detector switches between two or more settings of the ion gate open time based on a predetermined condition. Initially, the controller sets the gate width to a first value (e.g., a default gate width), and operates a pressure pulse generator to obtain 300 a material sample in a reaction zone, and operates an ionizer to produce ions that ionize the sample 302 in the reaction zone. The controller then operates 404 the gate using the first gate width, and selects 406 a corresponding analysis based on the gate width. The controller then detects the arrival of the ions at the collector electrode to generate a detection signal, such as an ion flow associated with the arrival of the ions at the collector. The controller analyzes 408 the detection signal in a set of time windows according to the selected analysis.

[0066] The controller then determines 410 whether to select a new gate width and performs further analysis. This may be done based on the results of the first analysis.

[0067] For example, in the event that a threshold is exceeded in a time window explicitly associated with a chemical hazard, the controller may trigger an alarm indicating the presence of the chemical hazard, in which case no additional gate width may be selected and the controller may perform 412 an action selected based on the time window in which the threshold has been exceeded.

[0068] On the other hand, where the results of the first analysis are somewhat ambiguous (e.g., a threshold is exceeded in a time window that may be associated with a particular hazard or a known interferent but both cannot be resolved), the controller selects 404 a second different gate width and selects 406 a second set of thresholds in the corresponding time window. The second gate width and the second set of thresholds can be configured for detecting a particular chemical hazard and / or for suppressing detection of interferents at the second gate width. In this case, the controller then operates 404 the spectrometer, selects a corresponding analysis 406, operates the spectrometer to detect ions, and analyzes the detection signal using a second analysis 408.

[0069] The results of the first analysis and the second analysis may then be used together to determine whether a particular chemical hazard is present.

[0070] The minimum detectable concentration of different threat agents strongly depends on the chemical nature of the material of interest. Experiments have shown that some threat agents can be detected at a first set of thresholds when the gate width is set to its lowest value. Other threat agents may require very long gate widths at those same thresholds.

[0071] It will be appreciated in the context of the present disclosure that dynamic adjustment of the detection algorithm may include activating and / or deactivating certain time windows for some of the threats of interest. For example, certain windows may only be used in certain configurations of the detector and not in other configurations. Typically, this is done based on the configuration of the detector (e.g., gate width).

[0072] As will be understood in the context of the above disclosure, the controller selects detection windows and amplitude thresholds in these time windows based on gate width. In some embodiments, in addition to adjusting the thresholds based on gate width, the detection logic can also be adjusted based on gate width. For example, the controller can be configured to trigger an alarm at a specific gate width only if a threshold is exceeded in a time window associated with the presence of a monomer peak of a specific chemical hazard and / or in a time window associated with a dimer peak of a specific chemical hazard. As another example, the detection logic for a specific gate width can include identifying the presence of a specific peak shape in a specific time window.

[0073] In the above-mentioned second embodiment, the controller is configured to perform a series of operation cycles of the detector, and use a corresponding sequence of gate widths and detection analysis for these operation cycles, so that different gate widths and different analyses are used in at least some cycles. For example, the controller is configured to operate the spectrometer to obtain a material sample in the reaction zone, and then operate the spectrometer to analyze the sample using a first gate width to obtain a first detection signal. These first detection signals are then analyzed using the corresponding analysis selected for the gate width (e.g., detection logic such as threshold, peak shape, deactivation time window, etc.).

[0074] The ion gate open time can be initially set to a default value, and the controller can apply a default analysis to the resulting detection signal. However, if no alarm is generated, the open time of the ion gate can be gradually increased to a maximum open time for detecting threats at a selected threshold concentration (such as a concentration of a hazard associated with one or more chemicals). If no alarm is generated, the detector can return to the original (default) configuration after several cycles. If an alarm is generated when the open time of the ion gate will be set to an intermediate value. The detector will remain in this configuration until the maximum amplitude threshold defined in the detection algorithm is reached, and then the detector will be restored to the original configuration to avoid saturation of the instrument. The detection window, amplitude threshold and logic defined in the algorithm will be related to the open time of the ion gate.

[0075] like Figure 1 As shown, the drift gas can flow from the end of the drift region closest to the collector electrode to the grid. In these embodiments, the time when the ions arrive at the collector electrode depends on the mobility of the ions. In other embodiments, there can be no drift gas, and the unit can be evacuated to provide a time to arrive at the collector electrode determined by the mass-to-charge ratio. For example, the mass spectrometer can be a TOF mass spectrometer.

[0076] In some examples, the functions of the controller 120 may be provided by a general-purpose processor that may be configured to perform a method according to any of those methods described herein. In some examples, the controller may include 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 may store data and / or program instructions for implementing the operations described herein. Embodiments of the present disclosure provide a tangible non-transitory storage medium including program instructions, which are operable to program a processor to perform any one or more of the methods described and / or claimed herein and / or provide a data processing device as described and / or claimed herein. The controller 120 may include an analog control circuit that provides at least a portion of the control function. An embodiment provides an analog control circuit that is configured to perform any one or more of the methods described herein. It should 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. In addition, without departing from the scope of the invention as defined in the appended claims, equivalents and modifications not described above may also be adopted.

Claims

1. A spectrometer for detecting a substance of interest, the spectrometer comprising: a chamber through which a plurality of sample ions travel from an ion grid to a collector electrode; a detector connected to the collector electrode for detecting the arrival of sample ions at the collector electrode; The controller is configured as: controlling parameters of the spectrometer to selectively increase or decrease the number of sample ions entering the chamber each time the ion gate is opened, detecting the arrival of the sample ions at the collector electrode to obtain a detection signal during a set of time windows after opening the ion gate, The detection signal in the time window is analyzed according to the parameters of the spectrometer to detect the presence of the substance of interest.

2. The spectrometer according to claim 1, wherein the parameters include at least one of the following: (i) Gate width, (ii) the amount of sample vapor introduced into the reaction zone containing the ionizer, and (iii) the duration that ions remain in the reaction zone before the ion gate is turned on.

3. The spectrometer according to claim 1 or 2, wherein analyzing the detection signal according to the parameter comprises: selecting at least one detection criterion based on the parameter, and The presence of the substance of interest is identified based on the detection signal and the at least one detection criterion. 4 . The spectrometer of claim 3 , wherein the at least one detection criterion comprises a detection threshold in at least one of the time windows.

5. The spectrometer of claim 4, wherein the at least one detection criterion comprises a marker associated with a substance of interest. The spectrometer of claim 5 , wherein the signature comprises an expected peak shape.

7. A spectrometer according to claim 5 or 6, wherein the signature comprises the presence of a monomer peak and / or a dimer peak associated with the substance of interest.

8. A spectrometer according to any preceding claim, wherein the controller is configured to select the time window in dependence on the parameter.

9. A spectrometer according to any preceding claim, wherein the controller is configured to: operating the spectrometer using first parameters to obtain a first detection signal, applying a first detection criterion to the first detection signal, and then The spectrometer is operated using second parameters to obtain a second detection signal, and a second detection criterion is applied to the second detection signal, wherein the second detection criterion is different from the first detection criterion.

10. The spectrometer of claim 9, wherein the first detection criterion comprises a first detection threshold for the time window.

11. A spectrometer according to claim 9 or 10, wherein the second detection criterion comprises a second detection threshold for the time window.

12. A spectrometer according to claim 9, 10 or 11, wherein the first detection criterion comprises a marker associated with a substance of interest for at least one of the time windows.

13. The spectrometer of any of claims 9 to 12, wherein the second detection criterion comprises a marker associated with a substance of interest for at least one of the time windows.

14. A spectrometer according to claim 12 or 13, wherein the signature comprises (a) an expected peak shape; and (b) the presence of a monomer peak or a dimer peak or both a monomer peak and a dimer peak.

15. The spectrometer of any of claims 9 to 14, wherein the first parameter is different from the second parameter.

16. A method for controlling a spectrometer, the spectrometer comprising: a chamber through which sample ions travel from an ion gate to a collector electrode, wherein the spectrometer is configured to distinguish the ions based on their travel time to the collector electrode; a detector connected to the collector electrode for detecting the arrival of sample ions at the collector electrode; The method includes: operating the spectrometer according to a first parameter and detecting the arrival of the sample ions at the collector electrode to obtain a first detection signal associated with the first parameter, operating the spectrometer according to a second parameter and detecting the arrival of the sample ions at the collector electrode to obtain a second detection signal associated with the second parameter, wherein the first parameter is different from the second parameter, wherein the detection signal comprises detecting the arrival of ions during a set of time windows after the ion gate is turned on, The method further includes analyzing the first detection signal according to a first detection criterion, and analyzing the second detection signal according to a second detection criterion, wherein the first detection criterion is different from the second detection criterion.

17. The method of claim 16, wherein the parameters include at least one of: gate width, (ii) the amount of sample vapor introduced into a reaction region containing an ionizer, and (iii) the duration that ions remain in the reaction region before the ion gate is turned on.

18. A method according to claim 16 or 17, wherein the first detection criterion comprises a first detection threshold for the time window.

19. A method according to any of claims 16 to 18, wherein the second detection criterion comprises a second detection threshold for the time window.

20. The method of any of claims 18 to 19, wherein the first detection criterion comprises a marker associated with a substance of interest for at least one of the time windows.

21. The method of any of claims 18 to 20, wherein the second detection criterion comprises a marker associated with a substance of interest for at least one of the time windows.

22. The method of claim 20 or 21, wherein the marker comprises an expected peak shape.

23. The method of claim 20, 21 or 22, wherein the signature comprises the presence of at least one of a monomer peak and a dimer peak.

24. The method of claim 23, wherein the signature comprises the presence of both the monomer peak and the dimer peak.

25. A computer program product comprising program instructions configured to program a controller of a spectrometer to perform the method according to any of claims 18 to 24, wherein the controller is connected to the detector and the ion grid of the spectrometer.

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