Method and apparatus for improving false alarm rate in trajectory detection - Patents.com

Abstract

An aspect of the disclosure provides a spectrometer for detecting a substance of interest comprising a chamber through which a number of sample ions pass as they travel from an ion gate to a collector electrode, a detector coupled to the collector electrode to detect the arrival of sample ions at the collector electrode, and a controller configured to control parameters of the spectrometer to selectively increase or decrease a number of sample ions entering the chamber each time the ion gate opens, detect the arrival of the sample ions at the collector electrode during a set of effective times following the opening of the ion gate to obtain a detection signal, and detect the presence of the substance of interest by analyzing the detection signal within the effective times in accordance with the parameters of the spectrometer.

Description

[Technical field]

[0001] The present invention relates to methods and apparatus. More particularly, the present invention relates to methods and apparatus for analyzing materials by detection of ions. Even more particularly, the present invention relates to methods employing analysis applied to a spectroscopic signal according to spectrometer parameters. [Background technology]

[0002] Ion mobility spectrometry (IMS) can identify substances (e.g., molecules, atoms, etc.) from a sample of interest by ionizing the substances and measuring the time it takes the resulting ions to travel a known distance through a countercurrent flow of drift gas under a known electric field. Typically, this time is measured from the time that an ion gate (also called an ion shutter) opens to the time that the ions reach a detector, e.g., a Faraday cup.

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

[0004] Some IMS cells have detectors that can collect ions and identify them by measuring their time of flight. This can be done in the presence of a drift gas so that mobility effects can separate the ions. Another type of detector measures the mass to charge ratio using the travel time through a chamber in the absence of drift gas and under an applied electric field. Such detectors may also be called time-of-flight mass spectrometers (TOF-MS).

[0005] These and other techniques are widely used for the detection of chemicals. One of the fundamental characteristics of a detector is its sensitivity. Sensitivity is a measure of the minimum detectable concentration of a substance of interest. Sensitivity is strongly related to the false alarm rate (FAR) of the device, and an increase in sensitivity often corresponds to an increase in the FAR. Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure aims to improve sensitivity and false alarm rate. [Means for solving the problem]

[0007] Aspects and examples 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 comprises: a chamber through which a number of sample ions pass as they travel from an ion gate to a collector electrode; a detector connected to the collector electrode to detect arrival of sample ions at the collector electrode; controlling a parameter of the spectrometer to selectively increase or decrease the number of sample ions entering the chamber each time the ion gate is opened; detecting arrival of the sample ions at the collector electrode during a set of effective times following the opening of the ion gate to obtain a detection signal; A controller is provided that is configured to detect the presence of the substance of interest by analyzing the detection signal within the multiple time periods according to the parameters of the spectrometer.

[0009] The parameters are: (i) Gate width, (ii) an amount of sample vapor introduced into a reaction region having an ionization device; and (iii) the period of time that ions are retained within the reaction region before opening the ion gate; may include at least one of:

[0010] While any one or more of these parameters can be used to increase or decrease the number of sample ions entering the chamber each time the ion gate is opened, the gate width is believed to be the most effective in a typical IMS system.

[0011] Analyzing the detection signal according to the parameters comprises: selecting at least one detection criterion based on said parameters; determining the presence of the substance of interest based on the detection signal and the at least one detection criterion.

[0012] For example, the detection criteria may include a detection threshold within a particular time window, or characteristics associated with the substance of interest. Such characteristics may include an expected peak shape. The controller may be configured to detect the peak shape. This may be performed based on a suitable Karp fit or fitting algorithm.

[0013] The features may include the presence of a monomer peak and / or a dimer peak for the substance of interest, for example a particular substance may be detected based on only the monomer peak of the particular substance, or based on only the dimer peak of the particular substance, or based on the presence of the monomer peak at one gate width and the presence of the dimer peak at a gate width different from the one gate width.

[0014] The controller may be configured to select the effective times according to the parameters and to disable some of the effective times when a gate width is used, for example, effective times associated with known interferents may be disabled.

[0015] The control device includes: operating the spectrometer with first parameters to obtain a first detection signal and applying a first detection criterion to the first detection signal; The spectrometer is configured to operate with second parameters to obtain a second detection signal and to apply a second detection criterion to the second detection signal, the second detection criterion being different from the first detection criterion.

[0016] The first detection criteria may include at least one of: (a) a first detection threshold for the plurality of effective times; (b) an expected peak shape of one or more of the plurality of effective times; and (c) enabling or disabling selected(s) of the effective times.

[0017] In one embodiment, a chamber through which the sample ions pass as they travel from the ion gate to the collector electrode; a detector connected to the collector electrode to detect arrival of sample ions at the collector electrode; The present invention provides a method of controlling a spectrometer comprising: a first electrode configured to identify ions based on their travel time to the collector electrode. The method comprises: operating the spectrometer with a first parameter and detecting arrival of the sample ions at the collector electrode to obtain a first detection signal related to the first parameter; A step of operating the spectrometer with a second parameter and obtaining a second detection signal related to the second parameter by detecting the arrival of the sample ions at the collector electrode, the second parameter being different from the first parameter. The detection signal comprises detection of the arrival of the sample ions at the collector electrode during a set of effective times following the opening of the ion gate. The method further comprises analysing the first detection signal according to a first detection criterion and analysing the second detection signal according to a second detection criterion, the second detection criterion being different from the first detection criterion.

[0018] As mentioned above, the parameters are generally: (i) Gate width, (ii) an amount of sample vapor introduced into a reaction region having an ionization device; and (iii) the period of time that ions are retained within the reaction region before opening the ion gate; may include at least one of:

[0019] Embodiments of the present disclosure provide a computer program product and a controller configured to control a spectrometer to perform one or more of the methods described herein. Typically, control logic is coupled to the detector and the ion gate of the spectrometer.

[0020] An embodiment varies the gate width (open time of the ion gate) between operations of the detector so that the detector can be operated at one gate width and then another gate width different from the one gate width. The change in gate width changes the sensitivity of the device accordingly. Different detection algorithms may be used for each of the two gate widths. Other sensitivity adjustment methods may also be used.

[0021] The embodiments relate to dynamic adjustment of the ion gate opening time (gate width) and the detection algorithm used. These embodiments may be used in an IMS.

[0022] Embodiments have the advantage that they can be used to detect a wide range of chemical threats at a wide range of concentrations without the user having to change the operating configuration.

[0023] Embodiments also have the advantage that adjustment of the detection algorithm can increase the dynamic range response of the detector to a particular chemical threat and / or increase sensitivity to chemical threats while controlling or avoiding sensitivity to interfering substances.

[0024] An aspect of the present disclosure provides a computer program product, such as a computer readable signal or a non-transitory tangible computer readable storage medium, having program instructions for programming a controller of an ion mobility spectrometer to perform any of the methods described or claimed herein.

[0025] Features of any one of the examples disclosed herein may be combined with selected features of any of the other examples described herein, for example features of the methods may be implemented in appropriately configured hardware, and specific hardware configurations described herein may be used in methods implemented using other hardware. [Brief description of the drawings]

[0026] Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. [Figure 1] 1 shows a cutaway view of an ion mobility spectrometer. [Diagram 2] FIG. 2 is a schematic diagram illustrating a detection window as employed in the methods and apparatus described herein. [Diagram 3] FIG. 1 shows two plots of detection signals obtained using two specific gate widths in the presence of a first specific chemical. [Figure 4] FIG. 2 is an illustration showing two plots of detection signals obtained using two particular gate widths in the presence of a second particular chemical. [Diagram 5] 2 is a flow chart showing modes of operation of a spectrometer as shown in FIG. 1; [Figure 6] 2 is a flow chart showing the modes of operation of a spectrometer such as that of FIG. 1;

[0027] In the drawings, like reference numbers are used to indicate like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The ion mobility spectrometer of FIG. 1 comprises a reaction region 102 , an ionization source 104 that ionizes a gaseous fluid within the reaction region 102 , an ion shutter 105 , a collector electrode 118 , such as a Faraday cup, and a controller 120 .

[0029] A controller 120 is connected to the ion shutter 105 and to the collector electrode for sensing the arrival of ions at the collector electrode. The controller may also be connected to operate the ionization source 104. In typical operation, the controller 120 provides a pulse or a train of pulses of the ionization source 104 each time a sample of gaseous fluid (such as a vapor) is provided to the reaction region. After each pulse, the controller 120 opens the ion shutter 105 after a "gate delay," the length of time that the shutter 105 is open being different from the gate delay and referred to as the "gate width" or gate open time.

[0030] During the gate width, ions generated in the reaction region 102 travel along the drift region 103 of the spectrometer from the reaction region 102 to the collector electrode. The number of ions passing through the gate into the drift region depends on the gate width. A larger gate width results in a larger number of ions and therefore a larger ion current at the collector electrode. Conversely, a smaller gate width results in a smaller number of ions and a smaller ion current. The sample ions are detected at the collector electrode, and a detection signal is obtained during a series of valid times following the opening of the ion gate.

[0031] The spectrometer comprises an enclosure, such as a tube 101. A reaction region 102 is at one end within the enclosure 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 enclosure 101 comprises an inlet 108 for introducing a sample of a gaseous fluid (vapor, gas, aerosol, etc.) into the reaction region 102.

[0032] The ion shutter 105 has two electrodes 106, 107. The two electrodes 106, 107 are coupled to the controller 120 so as to provide a barrier voltage therebetween. When the shutter 105 is in a "closed" state, the barrier voltage acts to prevent ions from moving from the reaction region to the drift region of the IMS, and when in an open state, the ions can move into the drift region toward the detector. The ion shutter 105 can include a Tyndall-Powell shutter, a Bradbury-Nielsen shutter, or other type of shutter. The shutter electrodes 106, 107 each have an elongated conductor, and the elongated conductor of the first shutter electrode 106 can be aligned in the drift direction with the elongated conductor of the second shutter electrode 107. The elongated conductors of each shutter electrode 106, 107 can be arranged as a grid, e.g., a regular or irregular mesh of triangles, rectangles, hexagons, etc. 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 (eg, sandwiched or interlaced) with one another.

[0033] The ionization source 104 is arranged to ionize the sample in the reaction region. In the example shown in Fig. 1, the ionization source 104 comprises a corona spot. The ionization source 104 is connected to a control device 120 such that the supply of electrical energy to the control device 120 can be controlled, for example by switching on the supply of pulses of power.

[0034] A voltage profile can be provided to the drift region 103 using an array 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 to 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 towards the detector 118. The electric field may be uniform and / or known along the drift region 103 and / or the reaction region 102.

[0035] The controller 120 comprises a programmable processor, an output interface such as a DAC capable of controlling the supply of suitable electrical control signals and / or power to the ion shutter and ionization source 104 (not shown in the drawings). Thus, the controller 120 is operable to operate the pulsed ionization source 104 and control the ion shutter. In general, the controller operates the pressure pulser to supply the sample to the reaction region. It then provides a series of operating cycles. During each cycle, the ionizer operates to ionize the sample. In each cycle of operation, a gate is opened to allow ions to move towards the collector and a detection signal is obtained at the collector electrode.

[0036] The controller 120 can store preset gate width values ​​and corresponding detection criteria associated with those gate widths. For example, the controller is configured such that a detection signal of one gate width is analyzed differently from a detection signal associated with a second, different gate width. Various different analyses are possible. As a first example, for a detection signal associated with a shorter gate width, the detection threshold at a selected effective time may be relatively low. In contrast, for a second detection signal obtained using a longer gate width, the threshold at those effective times may be higher and / or certain effective times may be ignored entirely. The controller is also configured to perform a particular action, such as issuing an alert indicating the presence of a particular hazardous chemical, based on a combination of one or more such analysis results.

[0037] 2 is a schematic diagram of a set of effective times 500, 502, 504, 506, 508, 512. As shown, each of these effective times corresponds to an interval between arrival times (drift times) at the collector. Such time intervals are typically measured from the operation (opening) of the gate. The detection signal during each effective time may be based on the amplitude of the ion current during that effective time.

[0038] FIG. 3 shows two plots 606, 608 on a pair of axes. The x-axis 604 shows the drift time and the y-axis shows the ion current measured at the detector. As the data is merely illustrative, both axes are unitless, but the scales applied to the two plots are equal to facilitate comparison. The first plot 606 shows the ion current measured at the collector using a first gate width. The second plot 608 shows the ion current measured at the collector for the same sample using a second gate width. The second gate width is longer than the first gate width. In both of the two plots, it can be seen that the monomer peaks associated with the chemicals in the sample are clearly detectable. However, in the data with the short gate width, the dimer peak is relatively low. For some chemicals, the monomer peak may overlap with an interfering chemical, so detection of the monomer peak alone may not be sufficient to unambiguously identify the presence of such a chemical. Therefore, detection of the dimer peak may be desired. To address this, the controller can be configured to switch to using a longer gate width if a detection threshold is reached in a time window associated with a monomer peak when using a shorter gate width. When analyzing detection signals collected using a longer gate width, the detection criteria used by the controller may include disabling (e.g., ignoring) valid times associated with the monomer peak and / or window(s) associated with known interferents.

[0039] FIG. 4 shows two plots 706, 708 on a pair of axes 700. The x-axis 604' shows drift time and the y-axis 602' shows ion current measured at the detector. As the data are merely illustrative, both axes are unitless, but the scales applied to the two plots are equivalent to facilitate comparison. The first plot 706 shows the ion current measured at the collector using a first gate width. The second plot 708 shows the ion current measured at the collector for 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 using the first gate width, the monomer peak may not be reliably distinguishable from the background signal. Thus, if the detection threshold is not met, the controller can be configured to increase the gate width and also provide a corresponding increase in the detection threshold for the associated effective time.

[0040] From the above discussion, it will be appreciated that the controller is configured to select the analysis to be used at each effective time depending on the gate width. This can be pre-set in such a way that a particular sequence of gate widths and corresponding detection criteria are pre-set for the detection of a particular hazardous chemical. For example, in a first analysis, the controller can use a first set of detection thresholds at effective times, where the thresholds at a particular effective time are selected based on the spread of a particular known interferent and based on the characteristics of the hazardous chemical to be detected.

[0041] The controller can then employ a sequence of gate widths and corresponding detection thresholds. These sequences can be provided in a variety of ways. The following will now be described with reference to two different embodiments of the method of operation of the spectrometer. In summary, these two embodiments are as follows: - Automatic switching of gate width and detection logic settings - Conditional switching of gate widths and detection logic, e.g., switching of gate widths and detection logic if a particular hazardous chemical is not detected using the default gate widths.

[0042] As shown in FIG. 5, in these first embodiments, the controller is configured to switch between using a default gate width and a first analysis in each time window, and to automatically switch between a different gate width and a corresponding different analysis. The controller sets the gate width to an initial value (e.g., the initial gate width), operates the pressure pulser to obtain a sample 300 of material in the reaction region, and operates the ionizer to generate ions that ionize the sample 302 in the reaction region. The controller then operates the gate using the initial gate width and selects a corresponding analysis based on the gate width. The controller then detects the arrival of ions at the collector electrode to generate a detection signal, such as an ion current, related to the arrival of ions at the collector. The controller analyzes the detection signals 306 at a series of effective times according to the selected analysis. The controller then automatically switches to using a second, different gate width and a corresponding second analysis. For example, the sample 308 can be further ionized in the reaction region and the gate 310 can be operated using a second gate width before detecting ions and analyzing the detection signal 312 using the second analysis. The controller may be configured to determine whether or not a hazardous chemical is present based on the results of the first analysis and / or the second analysis, for example, the two results may be used together to determine the presence or absence of a hazardous chemical and, for example, to generate an alert.

[0043] The second analysis may be selected depending on the second gate width. The controller may be configured to switch from the first gate width to the second gate width after a selected number of cycles of operation at the first gate width or after a selected time interval. There may be some conditionality in such a system. For example, if a hazardous chemical is detected in either of the two configurations, the controller may be configured to perform repeated cycles of operation in that configuration. This is done until a predefined maximum amplitude threshold is reached. Once the threshold is reached, the controller may switch back to the original configuration (first gate width, first analysis) to avoid saturation of the device if it is in the second configuration. Similarly, if no hazardous chemical is detected using the default gate width, the operation of the controller simply continues and automatically switches to use a second different gate width and a second analysis for an effective time. If no hazardous material is subsequently detected, the controller automatically returns to the first configuration. It will be understood in the context of the present disclosure that two or more different configurations may be used in this sequence such that the controller automatically switches between three or more different gate widths and applies a different analysis corresponding to the detection signal obtained at each different gate width.

[0044] FIG. 6 illustrates a second of the above embodiments. In this embodiment, the detector switches between two or more settings of the ion gate opening time based on some predefined condition. Initially, the controller sets the gate width to a first value (e.g., a default gate width), operates the pressure pulser to obtain a sample 300 of material in the reaction region, and operates the ionizer to generate ions that ionize the sample 302 in the reaction region. The controller then operates the gate 404 using the initial gate width and selects a corresponding analysis 406 based on the gate width. The controller then detects the arrival of the ions at the collector electrode and generates a detection signal, such as an ion current, associated with the arrival of the ions at the collector. The controller analyzes the detection signal at a series of effective times according to the selected analysis.

[0045] The controller then selects new gate widths and determines whether to perform further analysis, based on the results of the initial analysis.

[0046] For example, if the threshold is exceeded at a significant time that is clearly associated with a hazardous chemical, the controller may issue a warning indicating the presence of that hazardous chemical, in which case no further gate widths are selected, and the controller may perform an action selected according to the significant time that the threshold was exceeded.

[0047] On the other hand, if the first analysis result is ambiguous in some way (e.g., thresholds are exceeded at effective times that may relate to either a particular hazardous material or a known interferent, but cannot resolve both), the controller selects a second, different gate width 404 and a second set of respective effective time thresholds 406. The second gate width and second set of thresholds may be configured to detect the particular hazardous chemical and / or to suppress detection of interferents at the second gate width. In this case, the controller operates the spectrometer 404, selects a corresponding analysis 406, operates the spectrometer to detect ions, and analyzes the detection signal using a second analysis 408.

[0048] The results of the first and second analyses can then be used in combination to determine whether a particular hazardous chemical is present.

[0049] The minimum detectable concentration of each different hazardous substance strongly depends on the chemical properties of the substance of interest: some hazardous substances have been experimentally demonstrated to be detectable with the first set of thresholds when the gate width is set to the lowest value, while other hazardous substances are considered to require a much longer gate width at the same threshold.

[0050] In the context of the present disclosure, it will be understood that dynamic adjustment of the detection algorithm may include enabling and / or disabling of certain effective times for some of the hazardous materials of interest. For example, certain windows may only be used with certain configurations of the detector and not with others. Typically, this is done based on the configuration of the detector (e.g., gate width).

[0051] As understood in the context of the above disclosure, the controller selects the amplitude thresholds within the detection window and their effective times according to the gate width. In some embodiments, in addition to adapting the thresholds according to the gate width, the detection logic can also be adapted according to the gate width. For example, the controller may be configured to issue an alarm at a particular gate width only if the thresholds are exceeded at the effective times associated with the presence of a monomer peak and / or the effective times associated with a dimer peak of a particular hazardous chemical. As another example, the detection logic for a particular gate width may include identifying the presence of a particular peak shape at a particular effective time.

[0052] In the second embodiment, the controller is configured to execute a series of operating cycles of the detector and to use a sequence of gate widths and detection analyses corresponding to the operating cycles, with different gate widths and different analyses being used in at least some cycles. For example, the controller is configured to operate the spectrometer to obtain a sample of a substance in the reaction region, and then operate the spectrometer to analyze the sample using a first gate width to obtain first detection signals. These first detection signals are then analyzed using the corresponding analysis (e.g., detection logic such as threshold, peak shape, disabled valid time, etc.) selected for that gate width.

[0053] The ion gate opening time is initially set to a default value and the controller may apply a default analysis to the resulting detection signal. However, if no alarm occurs, the ion gate opening time may be increased in increments up to a maximum opening time used to detect hazardous materials at a selected threshold concentration (e.g., a hazardous concentration associated with one or more chemicals). If no alarm occurs, the detector may return to the original (default) configuration after several cycles. If an alarm occurs, the ion gate opening time is set to an intermediate value. The detector remains in that configuration until a maximum amplitude threshold defined in the detection algorithm is reached, after which the detector returns to the original configuration to avoid device saturation. The detection effective time, amplitude threshold, and algorithm-defined logic are correlated to the ion gate opening time.

[0054] As shown in Figure 1, the drift gas may flow from the end of the drift region closest to the collector towards the gate. In these embodiments, the arrival time of the ions at the collector electrode depends on the mobility of the ions. In other embodiments, there is no drift gas and the cell can be evacuated to provide an arrival time at the collector electrode determined by the mass to charge ratio. For example, the spectrometer may be a TOF mass spectrometer.

[0055] In some examples, the functionality of the controller 120 may be provided by a general-purpose processor, which may be configured to perform the methods according to any one of those described herein. In some examples, the controller may be configured by digital logic, such as a field programmable gate array, FPGA, application specific integrated circuit, ASIC, digital signal processor, DSP, or other suitable hardware. In some examples, one or more memory elements may store data and / or program instructions used to perform the operations described herein. An embodiment of the present disclosure provides a tangible non-transitory storage medium including 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 device described and / or claimed herein. The controller 120 may comprise an analog control circuit that provides at least a portion of this control functionality. An embodiment provides an analog control circuit configured to perform any one or more of the methods described herein.

[0056] It is to be understood that any feature described in connection with any one embodiment can be used alone or in combination with the other features described, and can also be used in combination with one or more features of any other of the embodiments, or in any combination of any other of the embodiments. Moreover, equivalents and modifications not described above may be employed without departing from the scope of the invention, which is defined in the appended claims.

Claims

1. A spectrometer for detecting substances of interest, A chamber through which numerous sample ions pass as they move from the ion gate to the collector electrode, A detector connected to the collector electrode to detect the arrival of sample ions at the collector electrode, The parameters of the spectrometer are controlled to selectively increase or decrease the number of sample ions entering the chamber each time the ion gate opens. During a set of effective time periods consisting of multiple effective time periods following the opening of the ion gate, the arrival of the sample ions at the collector electrode is detected to obtain a detection signal. The presence of the substance of interest is detected by analyzing the detection signals within the plurality of effective time periods according to the parameters of the spectrometer. A spectrometer equipped with a control device configured as follows.

2. A spectrometer according to claim 1, A spectrometer in which the parameters include at least one of (i) gate width, (ii) amount of sample vapor introduced into a reaction region having an ionizer, and (iii) duration for which ions are held in the reaction region before the ion gate opens.

3. A spectrometer according to claim 1 or 2, The step of analyzing the detection signal according to the aforementioned parameters is: A step of selecting at least one detection criterion based on the aforementioned parameters, A spectrometer comprising the step of identifying the presence of the substance of interest based on the detection signal and the at least one detection criterion.

4. A spectrometer according to claim 3, wherein the at least one detection criterion includes a detection threshold within the plurality of effective time intervals.

5. A spectrometer according to claim 4, wherein the at least one detection criterion includes characteristics relating to the substance of interest.

6. A spectrometer according to claim 5, wherein the feature includes a predicted peak shape.

7. A spectrometer according to claim 6, wherein the feature includes the presence of monomer and / or dimer peaks relating to the substance of interest.

8. A spectrometer according to claim 7, wherein the control device is configured to select the plurality of effective times according to the parameters.

9. A spectrometer according to claim 8, The control device is A first detection signal is obtained by operating the spectrometer with the first parameter, and a first detection criterion is applied to the first detection signal. A spectrometer configured to subsequently acquire a second detection signal by operating the spectrometer with a second parameter, and to apply a second detection criterion different from the first detection criterion to the second detection signal.

10. A spectrometer according to claim 9, wherein the first detection criterion includes a first detection threshold for the plurality of effective times.

11. A spectrometer according to claim 10, wherein the second detection criterion includes a second detection threshold for the plurality of effective times.

12. A spectrometer according to claim 11, wherein the first detection criterion includes features relating to the substance of interest during at least one of the plurality of effective times.

13. A spectrometer according to claim 12, wherein the second detection criterion includes features relating to the substance of interest during at least one of the plurality of effective times.

14. A spectrometer according to claim 13, wherein the feature includes at least one of (a) a predicted peak shape and (b) the presence of monomer peaks and / or dimer peaks.

15. A spectrometer according to claim 14, wherein the first parameter is different from the second parameter.

16. A chamber through which sample ions pass as they move from the ion gate to the collector electrode, A detector connected to the collector electrode to detect the arrival of sample ions at the collector electrode, A method for controlling a spectrometer comprising a, configured to identify ions based on the time it takes for the ions to travel to the collector electrode, A step of operating the spectrometer according to a first parameter and obtaining a first detection signal related to the first parameter by detecting the arrival of the sample ions at the collector electrode, The process includes a step of 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 related to the second parameter, which is different from the first parameter. The detection signal includes the detection of the arrival of the sample ions at the collector electrode during a set of valid time periods consisting of a plurality of valid time periods following the opening of the ion gate. A method further comprising the steps of analyzing the first detection signal according to a first detection criterion and analyzing the second detection signal according to a second detection criterion different from the first detection criterion.

17. The method according to claim 16, A method wherein the parameter includes at least one of (i) the gate width, (ii) the amount of sample vapor introduced into a reaction region having an ionizer, and (iii) the period of time the ions are held in the reaction region before the ion gate opens.

18. A method according to claim 16 or 17, wherein the first detection criterion includes a first detection threshold for the plurality of effective times.

19. A spectrometer according to claim 18, wherein the second detection criterion includes a second detection threshold for the plurality of effective times.

20. A method according to claim 19, wherein the first detection criterion includes features relating to the substance of interest during at least one of the plurality of effective times.

21. A spectrometer according to claim 20, wherein the second detection criterion includes features relating to the substance of interest during at least one of the plurality of effective times.

22. A method according to claim 21, wherein the feature includes a predicted peak shape.

23. A method according to claim 22, wherein the feature is the presence of at least one of monomeric peaks and dimeric peaks.

24. A method according to claim 23, wherein the feature is the presence of both monomeric and dimeric peaks.

25. A computer program product having program instructions for programming a control device of a spectrometer connected to the detector and the ion gate of the spectrometer to perform the method according to claim 24.

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