GB2617857A

GB2617857A - Collector for ion detection

Info

Publication number: GB2617857A
Application number: GB2205915.8A
Authority: GB
Inventors: Marmugi Luca; Procino Immacolata
Original assignee: Smiths Detection Watford Ltd
Current assignee: Smiths Detection Watford Ltd
Priority date: 2022-04-22
Filing date: 2022-04-22
Publication date: 2023-10-25
Also published as: WO2023203357A1; GB202205915D0

Abstract

An electrode forming a collector 118 for an ion detector, the detector detects ions based on their travel time to the collector, the collector comprising: an inner collection region 130, and an outer collection region 132, wherein the outer region is electrically isolated from the inner region; a first electrical connection 134 for connecting the inner region to detection electronics 140, and a second electrical connection 136 for connecting the outer region to the detection electronics; wherein the inner and outer regions each collect ions and provide a detection signal to the detection electronics in response to arrival of the ions at the collector. A further collector region 145 (Figure 2) may be provided electrically isolated from the inner and outer regions. The centre of the inner region may be aligned with the centre of an ion distribution travelling towards the collector. A controller 120 may adjust the sensitivity and resolution of the detected signals and may choose to obtain a signal only from one of the inner or outer regions or both.

Description

Collector for Ion Detection

Technical Field

The present invention relates to apparatus and methods for ion detection, and more particularly to ion collector plates for spectrometers, and their uses.

Background

Ion spectrometry techniques such as Ion Mobility Spectrometry (IMS) and Mass Spectrometry (MS) are analytical techniques used detect substances of interest. This can include the detection of dangerous, hazardous and illicit substances contained in a sample, for example in defence and security settings.

Such techniques may involve ionising a sample, and detecting ions from the sample at a collector plate by obtaining a voltage signal proportional to the number of detected ions (thereby providing an ion count). Detectors according to these techniques may measure the time it takes for ions from the sample to reach a collector, and use this information in combination with the ion count to characterise the sample, e.g. to identify the substances contained within the sample.

Among the operational parameters used for measuring the performance of these detectors, the signal-to-noise ratio (S/N) at a given concentration of the substance of interest (which sensitivity of the detector), and the resolution (or resolving power, R) are 25 important for assessing the capability of detecting and identifying a specific threat.

S/N indicates the ratio between the maximum signal produced by a specific analyte (typically, the amplitude of a corresponding peak in ion count) and the baseline level measured by the detector when no analyte is present. At a given concentration of analyte, this determines whether the substance of interest can be detected above the background signal level or not. This directly determines the Limit of Detection (LoD) of the detector, i.e. the smallest quantity or concentration of an analyte that can be reliably detected.

In detectors which utilise the travel time of ions to identify a substance of interest, the -2 -resolution R, is customarily defined as the ratio between the measured travel time of a specific analyte and the full width at half maximum of the corresponding IMS peak. R therefore relates to the capability of the detector to separate neighbouring peaks and, thus, to discriminate substances with similar travel times. This becomes a critical parameter when the identification of the threat is necessary to deploy the correct countermeasures, or when it is required to discriminate between actual threats and other substances, potentially harmless, in the environment (so-called interferents).

Both SIN and R are thus important to the performance of an ion spectrometry detector, but they heavily depend on intrinsic (e.g., details of the design, ionisation source, electric field, etc) as well as extrinsic (e.g., detector's settings, contamination, humidity, etc) factors. In particular, there is a known trade-off between SIN and R: increasing the quantity of ions allowed to enter a drift region of a detector may produce an increase of the signal level and thus an improvement of S/N, but may also cause a broadening of the IMS peaks which practically reduces R.

Summary of Invention

Embodiments of the present invention aim to address the above problems by providing a segmented collector plate in an ion detector that can be controlled to optimise SIN and R during the detection process. The inventors have surprisingly found that signal obtained from a region of the collector (e.g. an inner region) may exhibit improved resolution R compared to signal obtained from the collector plate as a whole, whilst signal from the collector as a whole may exhibit relatively better signal-to-noise ratio. Therefore, by providing a segmented collector plate in which the parts of the plate from which detection signals are obtained and/or used can be controlled, different operational modes which favour either high signal-to-noise ratio or high resolution can be selectively provided in a single device.

Aspects of the disclosure are set out in the independent claims and optional features are set out in the dependent claims. Aspects of the disclosure may be provided in conjunction with each other, and features of one aspect may be applied to other aspects.

In an aspect, there is provided a collector for an ion detector, the detector configured to 35 detect ions based on their travel time to the collector, the collector comprising: an inner -3 -region, and an outer region, wherein the outer region is electrically isolated from the inner region; a first electrical connection for connecting the inner region to detection electronics, and a second electrical connection for connecting the outer region to the detection electronics; wherein the inner region and the outer region are each arranged to collect ions and to provide a detection signal to the detection electronics in response to arrival of the ions at the collector.

The collector may be a collector electrode. The inner region and the outer region may each comprise a connection to a bias voltage supply to set each of the inner region and the outer region at a selected bias voltage. The connections to the bias voltage supply may be configured so that the outer region is electrically isolated from the inner region. The inner region and the outer region may be carried on the same substrate. The substrate may be made from an insulating material, for example, the substrate may be a printed circuit board. The inner region and outer region may be spaced apart on the substrate, for example such that the outer region and the inner region are electrically isolated from each other by the gap provided between them. The inner region and the outer region may be provided on a first side, e.g. face, of the substrate, and the electrical connections may be provided on a second side, e.g. face of the substrate, opposite the first side.

The first and second electrical connections may be operable to switchably connect at least one of the inner region and the outer region to an analogue-to-digital converter, ADC, or other detection electronics. The first and second electrical connection may comprise a switching device, for example a multiplexer, for switchably connecting at least one of the inner region and the outer region to the ADC. The multiplexer may be arranged to provide a single output signal (e.g. a multiplexed signal) to detection electronics, based on the signal obtained from both of the inner region and the outer region The first electrical connection may provide a connection to a corresponding input of a first ADC, and the second electrical connection may provide a connection to a corresponding input of a second ADC. Detection electronics may be arranged to combine data from the output of the first ADC with data from the output of the second ADC The collector may comprise a further region, electrically isolated from the inner region 35 and the outer region, and a third electrical connection for connecting the further region to -4 -the detection electronics. The further region may be arranged to collect ions and to provide a detection signal to the detection electronics in response to arrival of the ions at the collector electrode. The further region may be arranged either outside of the outer region; or between the inner region and the outer region. The further region may be configured to operate in the same way as the inner region and the outer region. For example it may be switchably connected to the detection electronics in the same way as the inner region and the outer region.

Multiple further regions, e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9 further regions, may be provided, in 10 addition to the inner region and the outer region, which are each arranged to collect ions and to provide a detection signal to the detection electronics, and which are electrically isolated from each of the other regions.

The inner region may be circular, and may be arranged at the centre of the collector. The outer region may be annular, e.g. a circular ring, and may surround the inner region. The further regions may also be annular, and may surround the inner region and one or more of the other ion collection regions. The collector regions may be provided as a series of concentric rings, e.g. wherein the inner region is provided as a circle and the other regions are provided as rings of different diameters. In other examples the regions may be oval-shaped or rectangular, e.g. where the inner region is circular and the outer region and optional further regions are oval-shaped or rectangular rings which surround the inner region.

In another aspect there is provided a detector configured to detect ions based on their travel time to a collector, the detector comprising: a collector; and a chamber, through which ions travel towards the collector electrode; wherein the collector comprises an inner region and an outer region, wherein the outer region is electrically isolated from the inner region; and wherein the inner region and the outer region are each connected to detection electronics for providing detection signals indicating arrival of the ions at the inner region or the outer region.

The detector may be an ion mobility spectrometer. In other examples the detector may be a mass spectrometer, for example a time of flight mass spectrometer.

The detector may further comprise an ion source, arranged to provide ions for entry into -5 -the chamber. The ion source may comprise an ioniser, operable to ionise a sample introduced into the detector. The detector may also comprise means for controlling the release of ions into the chamber. The means for controlling the release of ions into the chamber may comprise an ion gate. The means for controlling the release of ions into the chamber may comprise the ion source.

The detector may be configured to provide the ions along an ion path between the ion source and the collector. The centre of the inner region may be aligned with the centre of the ion path. For example the inner region may be aligned with the centre of the cross-sectional shape of the ion path, e.g. transverse to the direction of travel of the ions. The detector may be configured to provide an ion distribution between the ion source and the collector. The centre of the inner region may be aligned with the centre of the cross-section of the ion distribution. The ion distribution is formed when ions are allowed to pass the gate to travel towards the collector. Drift electrodes in the chamber and/or the disposition of the reaction region and/or the collector and any guard grid may determine the spatial disposition of this distribution.

The centre of the inner region may be disposed on a central axis of the detector and/or on a central axis of the chamber, e.g. transverse to the central axis.

The detector may further comprise a controller connected to control operation of at least one of: the inner region, the outer region, and the detection electronics. The controller may also be configured to control operation of the ion source and/or may be configured to control the means for controlling the release of ions into the chamber. The means for controlling the release of ions into the chamber may comprise an ion gate, and the controller may be configured to control the gate width provided from the ion gate.

The controller may be arranged to adjust the sensitivity and resolution of the detection signals obtained from the collector based on at least one of: the control of the inner region, the outer region, and/or the detection electronics; and the control of the gate width. The controller may be arranged to increase the sensitivity of the signals by increasing the gate width, and/or may be arranged to increase the resolution of the signals by reducing the gate width.

In the event that a detection signal based on ions collected from the inner region and the -6 -outer region provides an ambiguous identification of a substance, the controller may be configured to obtain a detection signal only from the inner region. Obtaining a detection signal only from the inner region may provide an increased resolution of the signals.

In the event that a detection signal provides an ambiguous identification of a substance, the controller may be configured to increase the gate width.

A detection signal which provides an ambiguous identification of a substance may include detection signals which have a lower resolution than a particular threshold 10 resolution, for example detection signals in which peaks of amplitude overlap more than a selected amount.

In a further aspect there is provided a method of operating an ion detector, the detector comprising a collector and a chamber through which ions travel to reach the collector, wherein the collector comprises an inner region and an outer region, wherein the outer region is electrically isolated from the inner region; the method comprising selecting between a first mode of operation and a second mode of operation to control at least one of the resolution and sensitivity of the detector, wherein the first mode comprises obtaining a total signal indicating total ion current obtained from the inner region and the outer region; and the second mode comprises obtaining a partial signal indicating ion current collected obtained only from one of the inner region and the outer region; the method further comprising providing data for use in identifying the presence of a substance of interest based on the obtained signal. Selecting between the first mode and the second mode may favour and/or optimise one of the resolution and sensitivity of the detector.

The method may further comprise determining, based on the total signal obtained in the first mode, whether to use the second mode of operation to obtain the partial signal. Determining whether to use the second mode may comprise using the second mode in 30 the event that the total signal provides ambiguous information.

Ambiguous information may include information which has a lower resolution than a selected threshold resolution, for example information in which peaks of amplitude overlap more than a selected amount. -7 -

The method may further comprise determining, based on the partial signal obtained in the second mode, whether to use the first mode of operation to obtain the total signal. Determining whether to use the first mode may comprise using the first mode in the event that the partial signal provides information below a required, e.g. a threshold, sensitivity, which may be selected.

The method may further comprise using both the total signal and the partial signal to identify the substance.

In a further aspect there is provided a method of operating an ion detector, the detector comprising a collector and a chamber through which ions travel to reach the collector, wherein the collector comprises an inner region and an outer region, wherein the outer region is electrically isolated from the inner region; the method comprising: operating the detector in a first mode to obtain a total signal indicating total ion current obtained from the inner region and the outer region; operating the detector in a second mode to obtain a partial signal indicating ion current obtained only from one of the inner region and the outer region; providing data for use in identifying the presence of a substance of interest based on at least one of the total signal or the partial signal.

The method may further comprise using both the total signal and the partial signal to identify a substance.

The method may further comprise selecting a gate width based on the obtained signal.

Obtaining a partial signal may comprise disconnecting the outer region from digitising electronics thereby to digitise only an electrical signal obtained from the inner region. Alternatively, obtaining a partial signal comprises digitising electrical signals obtained from the inner region separately from electrical signals obtained from the outer region.

Brief Description of Figures

Some examples of the present disclosure will now be described, by way of example only, with reference to the figures, in which: Figure 1 shows a cutaway view of an ion mobility spectrometer which includes a segmented collector; Figure 2 shows an example of a segmented collector electrode; Figure 3 is a flow chart illustrating a method of operation of an ion detector; Figure 4 is a flow chart illustrating another method of operation of an ion detector.

In the drawings like reference numerals are used to indicate like elements.

Specific Description

The present disclosure relates to segmented collector electrodes and their use in ion spectrometry devices.

Figure 1 shows a cut-away view of an ion mobility spectrometer (IMS) 100, which includes a segmented collector electrode 118. Although the structure and function of an IMS described in detail below, it will be appreciated that this is just one possible type of detector in which it is envisaged that a segmented collector according to the present disclosure could be used. For example, a segmented collector as described herein could also be used as the ion collector in a mass spectrometer (MS), for example a time-offlight mass spectrometer (TOFMS), or any other type of detector in which the travel time taken by ions to reach the collector is used to provide data for use in identifying the presence of a substance of interest.

The ion mobility spectrometer 100 of Figure 1 comprises a reaction region 102, an ion source 104, an ion gate 105, and a collector 118 separated from the ion gate 105 by a 25 drift region 103.

The IMS cell comprises a housing, such as a tube 101. The reaction region 102 is at one end inside this housing 101, and separated from a detector 118 by a drift region 103. The reaction region 102 is separated from the drift region 103 by the ion gate 105. The housing 101 comprises an inlet 108 for enabling a sample of gaseous fluid to be introduced into the reaction region 102.

The ion source 104 includes an ioniser that is arranged for ionising the sample in the reaction region 102. The ion source 104 is connected so that the controller 120 can 35 control the delivery of electrical energy to the controller 120, such as by switching on the supply of a pulse of electrical power.

The ion gate 105 comprises two electrodes which are coupled to the controller 120 to enable a barrier voltage to be provided between the two electrodes. When the gate 105 is "closed" this barrier voltage acts to prevent ions from travelling from the reaction region into a drift region of the IMS, and an open state in which ions can travel into the drift region towards the detector. The ion gate 105 may comprise a Tyndall-Powell, Bradbury-Nielsen gate, or other type of gate. The gate electrodes may each comprise elongate conductors, and the elongate conductors of the first gate electrode may be aligned in the drift direction with the elongate conductors of the second gate electrode. The elongate conductors of each gate electrode may be arranged as a grid, such as a mesh, for example a triangular, rectangular, hexagonal, or other regular or irregular mesh. The gate electrodes need not 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 interleaved or interwoven.

In the example illustrated in Figure 1, the drift region 103 lies between the reaction region 102 and a collector 118, the structure of which is described in more detail below.

A voltage profile may be provided in the drift region 103 using a series of drift electrodes 103a, 103b spaced apart along the drift region. Although not illustrated in Figure 1, a repeller plate or other electrode may 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 (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.

The controller 120 comprises a programmable processor, an output interface such as a DAC (not shown in the drawings) which is able to control the provision of appropriate electrical control signals and/or power supply to the ion gate 105 and the ion source 104. The controller 120 is thus operable to operate the ion source 104, and to control the ion gate 105.

The IMS 100 illustrated in Figure 1 may also comprise a drift gas inlet 122 into the drift -10 -region near the detector, and a drift gas outlet near the shutter so that a flow of (cleaned, dried) drift gas can be provided against the direction of travel of the ions towards the detector.

It will be appreciated that in other detectors according to the disclosure, e.g. detectors other than IMS devices, such as Mass Spectrometer, no drift gas is provided. For example in a Mass Spectrometry device such as a Time-of-flight Mass Spectrometer, the drift chamber may instead be held under vacuum.

The collector 118 is coupled to provide a signal to the controller 120, via detection electronics 140. Current flow from the collector 118 can be used by the controller 120 to infer that ions have reached the detector 118, and a characteristic of the ions can be determined based on the time for ions to pass from the gate 105 to the detector 118.

The collector 118 is an electrode which comprises an inner region 130 and an outer region 132 that are electrically isolated from one another. In Figure 1, the inner region 130 is circular and its centre is disposed on a central axis of the detector. In particular, the centre of the inner region is aligned with a central axis of the drift chamber 103. The outer region 132 is a ring that surrounds the inner region 130 and is concentric with it.

Although not shown in Figure 1, each of the inner region 130 and the outer region 132 include a connection to a bias voltage supply, in order to set both regions to a selected DC bias voltage. The connection provided between the inner region 130 and the bias voltage supply is also electrically isolated from the connection provided between the outer region 132 and the bias voltage supply.

The inner region 130 is connected to detection electronics 140 via a first electrical connection 134, and the outer region 132 is connected to the detection electronics 140 via a second electrical connection 136. The inner region 130 and the outer region 132 are thus each arranged to collect ions and to provide a detection signal to the detection electronics 140 in response to arrival of the ions at the collector electrode 118.

The detection electronics 140 are connected to the controller 120, to provide a detection signal to the controller 120. The detection electronics 140 includes an analogue-to-digital 35 converter, ADC, that is configured to convert the analogue signals provided from the collector 118 into digital signals, and to provide these signals to the controller 120.

The first connection 134 and the second connection 136 are operable to switchably connect the inner region 130 and the outer region 132 to the analogue-to-digital converter, ADC. As shown in Figure 1, the first connection 134 and the second connection 136 comprise a switching device 138, such as a multiplexer, for switchably connecting at least one of the inner region and the outer region to the ADC of the detection electronics 140.

In operation, the controller 120 operates the ioniser of the ion source to ionise the sample, and operates the ion gate 105 to introduce a pulse of ions into the drift chamber 103. These ions pass through the drift chamber 103 and are detected at the collector 118, which provides an ion current back to the controller 120 via detection electronics 140 The controller is operable to control the switching device 138, as well as the ion source 104 and/or the ion gate 105, based on the signals obtained from the detection electronics 140. For example, the controller 120 is operable to control the switching device so that either: * only detection signals from the inner region 130 are provided to the detection electronics 140; * only detection signals from the outer region 132 are provided to the detection electronics 140; or * detection signals from both the inner region 130 and the outer region 132 are provided to the detection electronics 140.

This is discussed in more detail below with reference to Figures 3 and 4.

The controller 120 is also connected to the ion gate 105, and is operable so as to control the gate width of the ion gate 105. The control of the ion gate may be based on the 30 detection signals obtained from the detection electronics 140.

Figure 2 shows an example collector electrode 200 which may be used as the electrode 118 in the IMS 100 of Figure 1. In addition to the inner region 130 and the outer region 132 shown in Figure 1, the collector electrode 200 also includes a further region 145 35 arranged as a further concentric ring which surrounds the inner region 130 and is itself -12 -surrounded by the outer region 132. In other examples the further region may be arranged as a further concentric ring which instead surrounds the outer region 132(and the inner region 130).

The further region 145 is also switchably connected to the detection electronics in the same way as the inner region 130 and the outer region 132 are, as discussed above with reference to Figure 1.

In the example shown in Figure 2, each of the regions 130, 132, 145 are carried on a 10 substrate 150, such as a printed circuit board. As shown, each of the regions 130, 132, 145 are provided on an insulating surface and separated from one another to provide a gap 160, such that the regions are electrically isolated from one another.

Each of the regions 130, 132, 145 are provided on a first side of the substrate 150, whilst other components, such as the detection electronics 140, switching device 138 and connections between the regions of the collector and the detection electronics (not shown in Figure 2 but discussed above with reference to Figure 1) are provided on a second side of the substrate 150, opposite the first side.

Each of the inner region 130, the outer region 132, and the further region 145, are electrically connected to a DC bias voltage supply, to set all the regions to a selected DC bias voltage. The connections between each of the regions 130, 132, 145, and the DC bias voltage supply are electrically isolated from one another.

Two possible methods of operation of a detector that includes a segmented collector will now be described with reference to Figures 3 and 4. Both of these figures illustrate methods of operating a detector, such as the IMS detector shown in Figure 1, that includes a segmented electrode such as those described above. However, the methods described below could also be performed by other types of ion detectors. For example, the methods described could also be performed by a mass spectrometer (MS), for example a time-of-flight mass spectrometer (TOFMS), or any other type of detector in which the travel time taken by ions to reach the collector is used to provide data for use in identifying the presence of a substance of interest.

In the method of Figure 3, in a first step 301, it is selected whether to operate the -13 -detector in a first mode of operation or a second mode of operation. The first mode of operation corresponds to a mode in which a total signal is obtained from both the inner region and the outer region of the collector. This total signal indicates the total, e.g. combined, ion current obtained from both the inner region and outer region of the 5 collector together. The second mode of operation corresponds to a mode in which a partial signal is obtained, which indicates the ion current obtained from only the inner region of the collector. Selecting between the two modes may therefore comprise operating the switching device 138 so that either current from both the inner region and the outer region is provided to the detection electronics, or only current from the inner 10 region is provided to the detection electronics. The switching device may be operated in this way in response to a control signal that it receives from the controller 120.

A second step 302 involves providing data for use in identifying the presence of a substance of interest based on the obtained signal. That is, based on the signal obtained 15 from whichever of the first mode and the second mode was selected in the first step 301, data is provided that can be used to identify the presence of a substance of interest.

The controller 120 may use this data to characterise the ions based on their travel time to the collector. For example, a peak in amplitude/ion count may be observed at a particular 20 travel time, where that travel time is the known travel time for a particular substance.

The data provided if the first mode is selected may be different from the data provided if the second mode is selected. In particular, it has been found that data obtained in the second mode, i.e. based on signals from only the inner region of the collector, has improved resolution (R) in comparison to data obtained in the first mode (which is based on signals from both the inner and outer regions of the collector). This means that the observed amplitude peaks may be narrower in the second mode in comparison to the first mode. This in turn may make it easier to distinguish between overlapping peaks and thereby to distinguish between a potentially harmful substance and a harmless interferent.

Conversely, the data obtained in the first mode may have improved the sensitivity/signalto-noise ratio in comparison to data obtained in the second mode. The total height of the amplitude peaks may therefore be greater in the first mode making it easier to distinguish 35 peaks from the background noise -14 -Therefore, in some examples the detector can firstly be operated in the first mode to obtain a total signal and provide data as set out above. It can then subsequently determined, based on this obtained data, whether to also then use the second mode of operation in order to obtain a partial signal from the inner region only. Such a determination may be performed, for example, if the total signal obtained in the first mode provides ambiguous information as to the presence of a substance of interest e.g. if the resolution R is not high enough as discussed above.

Alternatively, in other examples the detector can firstly be operated in the second mode to obtain a partial signal and provide data as set out above. It can then subsequently be determined, based on this obtained data, whether to also then use the first mode of operation in order to obtain a total signal from both the inner region and outer region of the collector. Such a determination may be performed, for example, if the partial signal obtained in the first mode provides data which is below a selected or desired sensitivity/signal-to-noise ratio.

The method illustrated in Figure 4, includes, as a first step 401 operating the detector in the first mode, and in a second step 402 operating the detector in the second mode.

These first and second modes correspond respectively to the first and second modes discussed above in relation to Figure 3. The order of steps 401 and 402 may be reversed such that in other examples, the detector is first operated in the second mode to obtain the partial signal, and is subsequently operated in the first mode to obtain the total signal. In step 403, data is provided for use in identifying the presence of a substance of interest based on at least one of the total signal obtained in the first mode or the partial signal obtained in the second mode.

In this example, both the total and partial signals are obtained, and may both be used, e.g. by the controller, to help identify a substance of interest.

For detectors which include an ion gate, the controller 120 is also configured to adjust the gate width, i.e. the duration of a pulse of ions provided by the ion gate towards the collector. The controller is configured to control the gate width in response to signals obtained from the collector, e.g. in either the first mode or the second mode. For example, in the event that the detector is operated in the second mode to obtain a partial -15 -signal from only the inner region, it may be determined that the information derived from the signal is below a selected sensitivity (i.e. below an acceptable signal-to-noise ratio). In response, as discussed above in relation to Figure 3, the detector can be operated in the first mode to obtain a total signal with improved sensitivity. Alternatively (or additionally), the controller can instead improve the sensitivity of the obtained signal by increasing the gate width of the ion gate. This improves the sensitivity as a greater number of ions are provided to the collector.

Alternatively, if the obtained signal in either the first mode or the second mode provides 10 ambiguous information, i.e. the resolution is below a selected level, the controller may reduce the gate width of the ion gate.

Obtaining a partial signal from the inner region can comprise disconnecting the outer region from digitising electronics thereby to digitise only an electrical signal obtained from the inner region. For example, the switching device arranged between the collector and the detection electronics can be operated so that only the signal from the inner region is provided to the electronics.

Alternatively, a partial signal from the inner region can be obtained by digitising both the 20 signal from the inner region and the signal from outer region, separately, and then separating the obtained signal from the inner region and the obtained signal from outer region in the digital domain.

The examples described above and shown in the figures include collectors which have two or three detection regions. However, other examples of segmented collectors are envisaged which include a greater number of regions, for example 4, 5, 6, 7, 8, 9 or more regions, where each region is arranged at a different distance from the centre of the detector, and optionally where each region surrounds those regions which are arranged at a smaller distance from the centre of the detector. However, it will be appreciated that it is not necessary that each region entirely surrounds those regions that are closer to the centre of the collector, e.g. it is not necessary that the outer region entirely surrounds the inner region, as long as the regions are arranged at different distances (e.g radial distances) from the centre of the collector.

In the examples described above, the terms "inner region" and "outer region" have been -16 -used to refer to individual electrically isolated detecting regions of the collector. However, these terms may instead refer to a plurality of such regions, and do not necessarily refer exclusively to the inner-most and outer-most regions of the detector. For example, in example collectors which include more than two regions, the "outer region" may include those regions of the detector which are arranged further from the centre of the detector than those regions which form the "inner region", which may include the inner-most region and optionally other regions that are arranged closer to the centre of the detector.

Although the examples illustrated in the Figures show circular inner regions and corresponding annular outer regions and other regions, other shapes are envisaged. For example the inner regions may be oval-shaped, square, or rectangular, and the outer regions and other regions may be correspondingly shaped "rings", e.g. which have outer edges which are correspondingly shaped. Regardless of the specific shape of the regions, the inner and outer regions may have the same aspect ratio.

It will be appreciated from the discussion above that the examples shown in the figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. In addition, the processing functionality may also be provided by devices which are supported by an electronic device. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. In some examples the function of one or more elements shown in the drawings may be integrated into a single functional unit.

As will be appreciated by the skilled reader in the context of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Any feature of any aspects of the disclosure may be combined with any of the other aspects of the disclosure. For example, method aspects may be combined with apparatus aspects, and features described with reference to the operation of particular elements of apparatus may be provided in methods which do not use those particular types of apparatus. In addition, each of the features of each of the examples is intended to be -17 -separable from the features which it is described in combination with, unless it is expressly stated that some other feature is essential to its operation. Each of these separable features may of course be combined with any of the other features of the examples in which it is described, or with any of the other features or combination of features of any of the other examples described herein. Furthermore, equivalents and modifications not described above may also be employed without departing from the invention.

Certain features of the methods described herein may be implemented in hardware, and one or more functions of the apparatus may be implemented in method steps. It will also be appreciated in the context of the present disclosure that the methods described herein need not be performed in the order in which they are described, nor necessarily in the order in which they are depicted in the drawings. Accordingly, aspects of the disclosure which are described with reference to products or apparatus are also intended to be implemented as methods and vice versa. The methods described herein may be implemented in computer programs, or in hardware or in any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such programs may be provided as signals or network messages and may be recorded on computer readable media such as tangible computer readable media which may store the computer programs in non-transitory form. Hardware includes computers, handheld devices, programmable processors, general purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and arrays of logic gates.

Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

Claims

-18 -Claims: 1. A collector for an ion detector, the detector configured to detect ions based on their travel time to the collector, the collector comprising: an inner region, and an outer region, wherein the outer region is electrically isolated from the inner region; a first electrical connection for connecting the inner region to detection electronics, and a second electrical connection for connecting the outer region to the detection 10 electronics; wherein the inner region and the outer region are each arranged to collect ions and to provide a detection signal to the detection electronics in response to arrival of the ions at the collector.
2. The collector of claim 1, wherein the inner region and the outer region each comprise a connection to a bias voltage supply to set each of the inner region and the outer region at a selected bias voltage.
3. The collector of claim 2, wherein the connections to the bias voltage supply are configured so that the outer region is electrically isolated from the inner region.
4. The collector of any preceding claim, wherein the inner region and the outer region are carried on the same substrate.
5. The collector of claim 4, wherein the inner region and the outer region are provided on a first side of the substrate, and the electrical connections are provided on a second side of the substrate, opposite the first side.
6. The collector of any preceding claim, wherein the first and second electrical connections are operable to switchably connect at least one of the inner region and the outer region to an analogue-to-digital converter, ADC.
7. The collector of claim 6, wherein the firstand second electrical connection comprise a multiplexer, for switchably connecting at least one of the inner region and the outer region -19 -to the ADC.
8. The collector of any of claims 1 to 5, wherein the first electrical connection provides a connection to a corresponding input of a first ADC, and the second electrical connection 5 provides a connection to a corresponding input of a second ADC.
9. The collector of any of claims 1 to 8, comprising a further region, electrically isolated from the inner region and the outer region, and a third electrical connection for connecting the further region to the detection electronics, wherein the further region is arranged to collect ions and to provide a detection signal to the detection electronics in response to arrival of the ions at the collector electrode.
10. The collector of claim 9, wherein the further region is arranged either: a) outside of the outer region; or b) between the inner region and the outer region.
11. A detector configured to detect ions based on their travel time to a collector, the detector comprising: a collector; and a chamber, through which ions travel towards the collector electrode; wherein the collector comprises an inner region and an outer region, wherein the outer region is electrically isolated from the inner region; and wherein the inner region and the outer region are each connected to detection electronics for providing detection signals indicating arrival of the ions at the inner region 25 or the outer region.
12. The detector of claim 11, wherein detector electrode comprises the detector electrode of any of claims 1 to 10
13. The detector of claim 11 or 12, further comprising an ion source, arranged to provide ions for entry into the chamber, and means for controlling the release of ions into the chamber.
14. The detector of any of claims 11 to 13, wherein the detector is configured to provide -20 -an ion distribution between the ion source and the collector, and wherein the centre of the inner region is aligned with the centre of the cross-section of the ion distribution.
15. The detector of any of claims 11 to 14, wherein the centre of the inner region is disposed on a central axis of the detector.
16. The detector of any of claims 11 to 15, further comprising a controller connected to control operation of at least one of: the inner region, the outer region, and the detection electronics.
17. The detector of claim 16 as dependent on claim 13, wherein the means for controlling the release of ions into the chamber comprises an ion gate, and wherein the controller is configured to control the gate width provided from the ion gate.
18. The detector of claim 17, wherein the controller is arranged to adjust the sensitivity and resolution of the detection signals obtained from the collector based on at least one of: the control of the inner region, the outer region, and/or the detection electronics; and the control of the gate width.
19. The detector of any of claims 16 to 18, wherein, in the event that a detection signal based on ions collected from the inner region and the outer region provides an ambiguous identification of a substance, the controller is configured to obtain a detection signal only 25 from the inner region.
20. The detector of any of claims 16 to 19, wherein, in the event that a detection signal provides an ambiguous identification of a substance, the controller is configured to increase the gate width.
21. A method of operating an ion detector, the detector comprising a collector and a chamber through which ions travel to reach the collector, wherein the collector comprises an inner region and an outer region, wherein the outer region is electrically isolated from the inner region; -21 -the method comprising selecting between a first mode of operation and a second mode of operation to control at least one of the resolution and sensitivity of the detector, wherein the first mode comprises obtaining a total signal indicating total ion current obtained from the inner region and the outer region; and the second mode comprises obtaining a partial signal indicating ion current collected obtained only from one of the inner region and the outer region; the method further comprising providing data for use in identifying the presence of a substance of interest based on the obtained signal.
22. A method of operating an ion detector, the detector comprising a collector and a chamber through which ions travel to reach the collector, wherein the collector comprises an inner region and an outer region, wherein the outer region is electrically isolated from the inner region; the method comprising: operating the detector in a first mode to obtain a total signal indicating total ion current obtained from the inner region and the outer region; operating the detector in a second mode to obtain a partial signal indicating ion current obtained only from one of the inner region and the outer region; providing data for use in identifying the presence of a substance of interest based on at least one of the total signal or the partial signal.
23. The method of claim 22, furthercomprising using both the total signal and the partial signal to identify the presence of a substance of interest.
24. The method of claim 21 further comprising determining, based on the total signal obtained in the first mode, whether to use the second mode of operation to obtain the partial signal.
25. The method of claim 24, wherein determining whether to use the second mode comprises using the second mode in the event that the total signal provides ambiguous information.
26. The method of claim 21 comprising determining, based on the partial signal -22 -obtained in the second mode, whether to use the first mode of operation to obtain the total signal.
27. The method of claim 26 wherein determining whether to use the first mode comprises using the first mode in the event that the partial signal provides information below a selected sensitivity.
28. The method of any of claims 24 to 27, further comprising using both the total signal and the partial signal to identify the presence of a substance of interest.
29. The method of any of claims 21 to 28, further comprising selecting a gate width based on the obtained signal.
30. The method of any of claims 21 to 29, wherein obtaining a partial signal comprises disconnecting the outer region from digitising electronics thereby to digitise only an electrical signal obtained from the inner region.
31. The method of any of claims 21 to 29, wherein obtaining a partial signal comprises digitising electrical signals obtained from the inner region separately from electrical signals 20 obtained from the outer region.