IMS analysis device and IMS analysis method

Abstract

To provide an IMS analyzer which is capable of identifying the component to be detected even when the peak corresponding to an ion generated from the component to be detected overlaps the peak corresponding to a primary ion.SOLUTION: An IMS analyzer according to the present invention comprises an ion source, a collector, an electrostatic gate electrode, an electrode for electric field formation, and a control unit. The control unit is provided so as to control the potential of the electrode for electric field formation so that a potential slope is formed in a drift region between the electrostatic gate electrode and the collector. The collector and the control unit are provided so as to measure the current waveform of a current that flows due to the ion reaching the collector. The control unit is provided so as to determine whether or not a second peak exists that overlaps a first peak in the current waveform. And, when it is determined that the second peak exists, the current waveform is measured by changing the potential of the electrode for electric field formation so that the inclination of the potential slope is reduced.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an IMS analysis device and an IMS analysis method. [Background technology]

[0002] Conventional IMS analyzers ionize sample gases using radiation, corona discharge, etc. Because radiation and corona discharge have high energy, the sample gas may be chemically decomposed during ionization. In this case, the detector detects many ions generated by the decomposition of the sample gas, resulting in many peaks (detection peaks) appearing in the IMS spectrum. This makes it difficult to identify the sample gas in IMS analysis. An IMS analyzer is known that ionizes a sample gas using low-energy electrons emitted from an electron-emitting element (see, for example, Patent Document 1). This analyzer can prevent the sample gas from chemically decomposing, making it easier to identify the sample gas. This IMS analyzer uses air as a carrier gas, and peaks corresponding to ions (primary ions) generated from the air appear in the IMS spectrum. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2019-186190 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional IMS analyzers sometimes measure IMS spectra in which peaks corresponding to ions generated from target components overlap with peaks corresponding to primary ions, making it difficult to identify the target components. The present invention has been made in consideration of the above circumstances, and provides an IMS analyzer that can identify a detection target component even when the peak corresponding to ions generated from the detection target component overlaps with the peak corresponding to primary ions. [Means for solving the problem]

[0005] The present invention provides an IMS analysis apparatus comprising an ion source, a collector, an electrostatic gate electrode, an electric field forming electrode, and a controller, wherein the controller is configured to control the potential of the electric field forming electrode so as to form a potential gradient in a drift region between the electrostatic gate electrode and the collector, the collector and the controller are configured to measure a current waveform of a current that flows when ions reach the collector, and the controller is configured to determine whether or not a second peak overlapping a first peak exists in the current waveform, and, if it is determined that a second peak exists, to change the potential of the electric field forming electrode so as to reduce the slope of the potential gradient, and measure the current waveform. [Effects of the Invention]

[0006] When the gradient of the potential gradient in the drift region is reduced and the current waveform (IMS spectrum) is measured, the time it takes for ions to travel from the electrostatic gate electrode to the collector is lengthened, improving the ion separation characteristics of the IMS analyzer. Therefore, if it is determined that a second peak overlaps with the first peak in the IMS spectrum obtained in the first measurement, the second peak can be separated from the first peak in the IMS spectrum obtained in the second measurement, making it possible to identify and quantify the target component using the second peak. This makes it possible to identify target components that were previously impossible to identify. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of an IMS analyzer according to one embodiment of the present invention. [Figure 2]1 is a flowchart of a method for controlling an IMS analyzer according to one embodiment of the present invention. [Figure 3] 1 is a graph showing changes in IMS spectra. DETAILED DESCRIPTION OF THE INVENTION

[0008] The IMS analyzer of the present invention comprises an ion source, a collector, an electrostatic gate electrode, an electric field forming electrode, and a controller, wherein the controller is configured to control the potential of the electric field forming electrode so as to form a potential gradient in a drift region between the electrostatic gate electrode and the collector, the collector and the controller are configured to measure a current waveform of a current that flows when ions reach the collector, and the controller is configured to determine whether or not a second peak overlapping a first peak exists in the current waveform, and, if it is determined that a second peak exists, to change the potential of the electric field forming electrode so as to reduce the slope of the potential gradient, and measure the current waveform. IMS is an abbreviation for Ion Mobility Spectrometry. When the first peak corresponds to an ion generated from a component contained in the carrier gas, the second peak may correspond to an ion generated from a component contained in the sample gas. When a plurality of ions are generated from the component contained in the sample gas and there are peaks corresponding to these ions, both the first peak and the second peak may correspond to ions generated from the component contained in the sample gas.

[0009] Preferably, the IMS analyzer of the present invention further includes a sample gas injector, wherein the collector, the electrostatic gate electrode, and the electric field generating electrode are housed in an analysis chamber, the sample gas injector is configured to inject a mixed gas of a sample gas and a carrier gas or a carrier gas not containing the sample gas into the analysis chamber, the ion source is configured to directly or indirectly ionize components contained in the sample gas or components contained in the carrier gas, the first peak corresponds to ions generated from the components contained in the carrier gas, and the second peak corresponds to ions generated from the components contained in the sample gas, and the control unit is configured to determine whether or not a second peak exists by comparing the current waveform measured when the carrier gas not containing the sample gas is injected into the analysis chamber with the current waveform measured when the mixed gas is injected into the analysis chamber. This allows accurate determination of whether or not a second peak exists that overlaps with the first peak.

[0010] Preferably, the ion source is an electron-emitting element, the electron-emitting element having a lower electrode, a surface electrode, and an intermediate layer arranged between the lower electrode and the surface electrode, the control unit is configured to apply a voltage between the lower electrode and the surface electrode, and the carrier gas is air containing moisture. Preferably, the control unit and the sample gas injector are configured to adjust the voltage applied between the lower electrode and the surface electrode so that the peak height or peak area of ​​the first peak approaches a target value when a carrier gas not containing the sample gas is injected into the analysis chamber, and are configured to inject the mixed gas into the analysis chamber and measure the current waveform after adjusting the voltage applied between the lower electrode and the surface electrode. This makes it possible to stabilize the amount of primary ions produced and quantitatively measure the components to be detected.

[0011] Preferably, the control unit is configured to determine whether or not a minute peak exists in the current waveform measured while the mixed gas is being injected into the analysis chamber, and if it determines that a minute peak does not exist, to increase the voltage applied between the lower electrode and the surface electrode. This makes it possible to increase the detection sensitivity of the IMS analysis device as needed, and to identify components that could not be identified with conventional IMS devices.

[0012] The present invention includes the steps of: measuring a current waveform of a current that flows when ions reach a collector while a mixed gas of a sample gas and a carrier gas is being injected into an analysis chamber; The present invention also provides an IMS analysis method, which includes the steps of: determining whether or not a second peak overlapping a first peak exists in the current waveform; and, if it is determined that a second peak overlapping the first peak exists, changing the potential of the electric field forming electrode so that the gradient of the potential gradient in the drift region between the electrostatic gate electrode and the collector becomes smaller, and measuring the current waveform of the current that flows when ions reach the collector. The IMS analysis method of the present invention preferably further comprises a step of measuring the current waveform of the current that flows when ions reach the collector while a carrier gas that does not contain a sample gas is being injected into the analysis chamber, and by comparing the current waveform measured while the carrier gas that does not contain the sample gas is being injected into the analysis chamber with the current waveform measured while the mixed gas is being injected into the analysis chamber, it is determined whether or not a second peak overlaps the first peak.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The configurations shown in the drawings and the following description are examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

[0014] FIG. 1 is a schematic cross-sectional view of the IMS analyzer of this embodiment. The IMS analyzer 40 of this embodiment comprises an ion source 1, a collector 6, an electrostatic gate electrode 8, electric field forming electrodes 9a to 9h, and a control unit 12. The control unit 12 is configured to control the potentials of the electric field forming electrodes 9a to 9h so as to form a potential gradient in the drift region 11 between the electrostatic gate electrode 8 and the collector 6. The collector 6 and the control unit 12 are configured to measure the current waveform of a current that flows when ions reach the collector 6. The control unit 12 is configured to determine whether or not a second peak overlapping a first peak exists in the current waveform, and, if it is determined that a second peak exists, to change the potentials of the electric field forming electrodes 9a to 9h so as to reduce the slope of the potential gradient, and measure the current waveform.

[0015] The IMS analyzer 40 of this embodiment is an apparatus that ionizes a sample gas and analyzes its mobility. The analyzer 40 may be a drift tube type IMS analyzer that performs analysis using a drift tube type IMS. The sample gas analyzed by the IMS analyzer 40 may be a gas sample or a vaporized liquid sample.

[0016] The control unit 12 is a part that controls the IMS analyzer 40. The control unit 12 may include, for example, a microcontroller having a CPU, memory, timer, input / output ports, etc. The control unit 12 may also include an electric field control unit 26, a gate control unit 27, an element voltage control unit 17, a recovery current measurement unit 19, a power supply unit, etc.

[0017] The ion source 1 is a part provided to ionize components contained in a sample gas or components contained in a carrier gas, and is, for example, an electron emitter 2, a corona discharge electrode, a radiation source, etc. In the following explanation, an IMS analysis apparatus 40 using an electron emitter 2 as the ion source 1 will be described.

[0018] The IMS analyzer 40 of this embodiment has an analysis chamber 30 that analyzes target components contained in sample gas. The analysis chamber 30 has an ionization region 10 between an electron emitter 2 and a collector 6 for ionizing the target components contained in the sample gas to generate ions (negative ions or positive ions), and a drift region 11 (ion migration region) for moving and separating the ions. An electrostatic gate electrode 8 is provided between the ionization region 10 and the drift region 11. An electron emitter 2 is disposed on the side of the ionization region 10 opposite the electrostatic gate electrode 8, with the surface electrode 4 facing the ionization region. A collector 6 is disposed on the side of the drift region 11 opposite the electrostatic gate electrode 8. The electron emitter 2, collector 6, electric field forming electrodes 9a to 9h, electrostatic gate electrode 8, etc. are housed in the analysis chamber 30.

[0019] The sample gas injector 16 is a part that injects a sample gas or a carrier gas into the analysis chamber 30. The sample gas injector 16 may also be configured to inject a mixed gas of a sample gas and a carrier gas, or a carrier gas that does not contain the sample gas, into the analysis chamber 30. For example, during calibration before measuring the sample gas, the sample gas injector 16 can inject a carrier gas that does not contain the sample gas into the analysis chamber 30. When measuring the sample gas, the sample gas injector 16 can inject a mixed gas of a sample gas and a carrier gas into the analysis chamber 30. The flow rate of the gas supplied to the analysis chamber 30 by the sample gas injector 16 is, for example, 200 mL / min. The components to be detected contained in the sample gas are analyzed by ion mobility spectrometry. If the sample is a gas, the sample gas injector 16 can be configured to continuously supply the sample gas to the analysis chamber 30. If the sample is a liquid, the sample gas injector 16 can have a vaporization chamber, and the sample gas vaporized in this vaporization chamber can be injected into the analysis chamber 30. The carrier gas is a gas, such as air containing moisture, that is injected into the analysis chamber 30 together with the sample gas. Components contained in the carrier gas are ionized by the electrons emitted from the electron emitter 2 to generate primary ions.

[0020] The drift gas injector 15 is a component provided to inject drift gas into the analysis chamber 30. The drift gas is a gas that flows in the drift region 11 in the opposite direction to the ion movement direction (from the electrostatic gate electrode 8 to the collector 6) and acts as a resistance to the ions as they move through the drift region 11. The drift gas may be purified atmospheric air (clean air), air supplied from a compressed air cylinder, or purified air exhausted from the analysis chamber 30 by the exhaust unit 20. The flow rate of the drift gas supplied by the drift gas injector 15 to the analysis chamber 30 can be greater than the flow rate of the gas supplied by the sample gas injector 16 to the analysis chamber 30. The flow rate of the drift gas is, for example, 500 mL / min.

[0021] The exhaust unit 20 is a part provided to exhaust gas from the analysis chamber 30. The exhaust unit 20 is provided to exhaust the drift gas and the sample gas from the analysis chamber 30. The exhaust unit 20 may be provided to forcibly exhaust the gas from the analysis chamber 30 using an exhaust fan or the like, or may be provided to naturally exhaust the gas from the analysis chamber 30.

[0022] The sample gas inlet 16 and exhaust 20 can be provided so that the sample gas flows through the ionization region 10. This allows the electrons emitted from the surface electrode 4 of the electron emitter 2 in the ionization region 10 to directly or indirectly ionize components contained in the sample gas, generating negative ions or positive ions.

[0023] The drift gas injection unit 15 and the exhaust unit 20 are provided so that the drift gas flows from the collector side toward the electrostatic gate electrode side in the drift region 11. For example, the drift gas injection unit 15 can be provided so as to supply the drift gas to the drift region 11 from the collector side, and the exhaust unit 20 can be provided so as to exhaust the drift gas from an opening (gas outlet) in the housing 28 around the ionization region 10.

[0024] The electron-emitting element 2 is an element configured to emit electrons from the surface electrode 4, and is an element that uses the emitted electrons to directly or indirectly ionize the components to be detected contained in the sample gas, thereby generating negative ions or positive ions. The electron-emitting element 2 has a lower electrode 3, a surface electrode 4, and an intermediate layer 5 disposed between the lower electrode 3 and the surface electrode 4.

[0025] The surface electrode 4 is an electrode located on the surface of the electron emitter 2. The surface electrode 4 may preferably have a thickness of 10 nm or more and 100 nm or less. The surface electrode 4 may be made of, for example, gold or platinum. The surface electrode 4 may also be made of multiple metal layers. Even if the surface electrode 4 has a thickness of 40 nm or more, it may have multiple openings, gaps, or thinned portions with a thickness of 10 nm or less. Electrons that flow through the intermediate layer 5 can pass through or penetrate these openings, gaps, or thinned portions, and can be emitted from the surface electrode 4. Such openings, gaps, or thinned portions can also be formed by applying a device voltage between the lower electrode 3 and the surface electrode 4.

[0026] The lower electrode 3 is an electrode that faces the surface electrode 4 via the intermediate layer 5. The lower electrode 3 may be a metal plate, or a metal layer or a conductive layer formed on an insulating substrate or a film. When the lower electrode 3 is made of a metal plate, this metal plate may also be the substrate of the electron-emitting element 2. The material of the lower electrode 3 is, for example, aluminum, stainless steel, nickel, or the like. The thickness of the lower electrode 3 is, for example, 200 μm or more and 1 mm or less.

[0027] The intermediate layer 5 is a layer in which electrons flow due to an electric field formed by applying an element voltage between the surface electrode 4 and the lower electrode 3. The intermediate layer 5 may be semiconductive. The intermediate layer 5 may contain at least one of an insulating resin, insulating fine particles, and a metal oxide. The intermediate layer 5 preferably contains conductive fine particles. The thickness of the intermediate layer 5 may be, for example, 0.5 μm or more and 1.8 μm or less. The intermediate layer 5 is, for example, a silicone resin layer having silver fine particles dispersed therein.

[0028] The electron emitter 2 may have an insulating layer 29 between the surface electrode 4 and the lower electrode 3. This insulating layer 29 may have an opening. The opening in the insulating layer 29 is provided so as to define the electron emission region of the surface electrode 4. Since electrons cannot flow through the insulating layer 29, electrons flow into the intermediate layer 5 corresponding to the opening in the insulating layer 29 and are emitted from the surface electrode 4. Therefore, by providing the insulating layer 29 with an opening, the electron emission region formed in the surface electrode 4 is defined. The electron emission region may be, for example, a 5 mm square area, and can be freely designed in accordance with the openings of the electric field forming electrodes 9a to 9h and the size of the collector 6.

[0029] The surface electrode 4 and the lower electrode 3 can be electrically connected to the control unit 12 (element voltage control unit 17). The device voltage control unit 17 is provided to control the magnitude of the device voltage (driving voltage of the electron-emitting device 2) applied between the surface electrode 4 and the lower electrode 3. When the potential of the lower electrode 3 is made substantially the same as the potential of the surface electrode 4 using the device voltage control unit 17 (the device voltage is made 0 V), no current flows in the intermediate layer 5 and no electrons are emitted from the electron-emitting device 2.

[0030] When an element voltage (driving voltage) is applied between the lower electrode 3 and the surface electrode 4 using the element voltage control unit 17 so that the potential of the lower electrode 3 is lower than the potential of the surface electrode 4, a current flows through the intermediate layer 5, and electrons that have flowed through the intermediate layer 5 pass through the surface electrode 4 and are emitted into the ionization region 10. The element voltage applied between the lower electrode 3 and the surface electrode 4 to emit electrons from the electron-emitting element 2 can be, for example, 5 V or more and 40 V or less, and preferably 10 V or more and 18 V or less. Adjusting the magnitude of the device voltage using the device voltage control unit 17 changes the current flowing through the intermediate layer 5, thereby changing the amount of electrons emitted from the electron-emitting device 2. Therefore, by increasing the device voltage, the amount of ions generated in the ionization region 10 can be increased, and the peak intensity of the peak appearing in the IMS spectrum measured using the recovery current measurement unit 19 can be increased (detection sensitivity is improved). However, increasing the device voltage also increases the half-width of the peak appearing in the IMS spectrum. This is thought to be because increasing the device voltage increases the amount of ions passing through the electrostatic gate electrode 8, thereby increasing the initial half-width immediately after passing through the gate. Furthermore, increasing the half-width of the peak appearing in the IMS spectrum increases the possibility of multiple peaks overlapping. Furthermore, when the magnitude of the device voltage is adjusted, the energy of the electrons emitted from the electron-emitting device 2 also changes.

[0031] When a carrier gas (air containing moisture) not containing sample gas is injected into the analysis chamber 30 using the sample gas injection unit 16 and a drift gas (air) is injected into the analysis chamber 30 using the drift gas injection unit 15, when electrons are emitted from the electron emitter 2 into the ionization region 10, the electrons immediately collide with air components and form primary ions (negative ions or positive ions). When the electrons emitted from the electron emitter 2 attach to gas components near the surface electrode 4 (electron attachment phenomenon), negative ions of the gas components are generated. When the energy of the electrons emitted from the electron emitter 2 is higher than the ionization energy of the gas components near the surface electrode 4, positive ions of the gas components are generated. These generated primary ions move toward the electrostatic gate electrode 8 due to the electric field formed in the analysis chamber 30. The primary ions are, for example, oxygen ions obtained by ionizing oxygen gas in the air. In this case, the ionized region 10 contains primary ions in an amount corresponding to the amount of electrons emitted by the electron emitter 2. The amount of the primary ions can be adjusted by adjusting the device voltage applied between the surface electrode 4 and the lower electrode 3 (by adjusting the amount of electrons emitted from the electron-emitting device 2).

[0032] When a mixed gas of sample gas and carrier gas (air containing moisture) is injected into the analysis chamber 30 using the sample gas injector 16 and drift gas (air) is injected into the analysis chamber 30 using the drift gas injector 15, electrons are emitted from the electron emitter 2 into the ionization region 10. The electrons immediately collide with air components to generate primary ions (negative or positive ions). These primary ions are driven toward the electrostatic gate electrode 8 by the electric field formed in the analysis chamber 30. Furthermore, these primary ions transfer charge to the target component contained in the sample gas in the ionization region 10, generating negative or positive ions of the target component (ion-molecule reaction). In other words, the electron emitter 2 can be used to indirectly generate negative or positive ions of the target component contained in the sample gas in the ionization region 10. At this time, the ionization region 10 contains both ions generated from the target component contained in the sample gas and primary ions. Furthermore, when the emitted electrons from the electron emitter 2 directly collide with the detection target component, negative or positive ions of the detection target component contained in the sample gas can be directly generated.

[0033] The electric field forming unit 7 is a part for forming a potential gradient in the region between the electron emitter 2 and the collector 6. The electric field forming unit 7 is provided to form a potential gradient that causes ions to move from the electron emitter side to the collector side. When the IMS analyzer 40 detects negative ions (negative ion mode), the control unit 12 (electric field control unit 26) applies a voltage to the electric field forming unit 7 so as to form a potential gradient that makes the potential on the electron emitter side lower than the potential on the collector side. When the IMS analyzer 40 detects positive ions (positive ion mode), the control unit 12 (electric field control unit 26) applies a voltage to the electric field forming unit 7 so as to form a potential gradient that makes the potential on the electron emitter side higher than the potential on the collector side.

[0034] The electric field forming unit 7 may include a plurality of electric field forming electrodes 9a-9h. The electric field forming electrodes 9a-9h may have any shape as long as they can form a potential gradient in the region between the electron emitter 2 and the collector 6. For example, they may be ring-shaped or arch-shaped. The electric field forming electrodes 9a-9h are arranged in a row so that an ionization region 10 and a drift region 11 (ion migration region) are formed inside the ring or arch. The electric field forming electrodes 9a-9h constituting the electric field forming unit 7 are electrically connected to the electric field control unit 26 of the control unit 12. The grid electrode 25, the collector 6, the surface electrode 4 of the electron emitter 2, or the lower electrode 3 may function as the electric field forming unit 7. The control unit 12 can form a potential gradient in the ionization region 10 and the drift region 11 by controlling the potentials of the electric field forming electrodes 9a to 9h, the surface electrode 4 of the electron emitter 2, and the like.

[0035] Two adjacent electric field forming electrodes 9a-9h included in the electric field forming unit 7 can be electrically connected with a resistor sandwiched therebetween, thereby generating a potential difference between the two adjacent electric field forming electrodes 9a-9h, and generating this potential difference between the respective electrodes can form a potential gradient in the region between the electron emitter 2 and the collector 6.

[0036] For example, in the analysis device 40 shown in FIG. 1, the electric field generating unit 7 includes multiple electric field generating electrodes 9a-9h, and two adjacent electric field generating electrodes 9a-9h are electrically connected via a resistor. Furthermore, the electrode 9h closest to the collector 6 among the multiple electric field generating electrodes 9a-9h is electrically connected to a grid electrode 25 via a resistor. The grid electrode 25 is connected to ground, for example, via a resistor. The potential of the electrode 9a farthest from the collector 6 can be controlled by the control unit 12. For example, the control unit 12 can apply a drift voltage so that the potential of the electrode 9a is, for example, −3000 V. The grid electrode 25 is connected to ground via a resistor, so that the potential is close to 0 V. Furthermore, because two adjacent electric field generating electrodes 9a-9h are electrically connected via a resistor, the potential of the multiple electric field generating electrodes 9a-9h arranged in a row increases in a stepwise manner as they approach the collector 6. Therefore, a potential gradient can be formed in the region (ionization region 10 and drift region 11) between the electron emitter 2 and the collector 6, in which the potential gradually increases as the distance to the collector 6 approaches. However, this potential gradient changes in the vicinity of the electrostatic gate electrode 8 depending on the potential of the electrostatic gate electrode 8. Furthermore, the control unit 12 can control the potential of the electron emitter 2 in consideration of the potential gradient formed by the plurality of electric field forming electrodes 9a to 9h. Furthermore, the electron emitter 2 functions as a part of the electric field forming unit 7, and the plurality of electric field forming electrodes 9a to 9h and the electron emitter 2 can cooperate to form a potential gradient.

[0037] The electrostatic gate electrode 8 is an electrode disposed between the ionization region 10 and the drift region 11, and controls the injection of ions generated in the ionization region 10 into the drift region 11 by utilizing the electrostatic interaction between the ions and the electrostatic gate electrode 8. The electrostatic gate electrode 8 is, for example, a grid-shaped electrode (shutter grid). The electrostatic gate electrode 8 can be arranged in a row together with the plurality of electric field generating electrodes 9a to 9h that make up the electric field generating unit 7. The electrostatic gate electrode 8 can be electrically connected to the gate control unit 27 of the control unit 12. The electrostatic gate electrode 8 is provided so as to be able to change the potential gradient formed by the electric field generating unit 7.

[0038] The gate control unit 27 changes the potential of the electrostatic gate electrode 8 to instantaneously change the state from low potential side closed (a state in which the potential of the electrostatic gate electrode 8 is low and ions in the ionization region 10 cannot pass through the electrostatic gate electrode 8 and move to the drift region 11) to high potential side closed (a state in which the potential of the electrostatic gate electrode 8 is high and ions in the ionization region 10 cannot pass through the electrostatic gate electrode 8 and move to the drift region 11), or to instantaneously change from high potential side closed to low potential side closed. This allows the electrostatic gate electrode 8 to be in an open state for only a very short time, and ions in the ionization region 10 can be injected into the drift region 11 only during this short time. Therefore, ions in the ionization region 10 can be injected into the drift region 11 in a single pulse.

[0039] The negative or positive ions injected into the drift region 11 migrate through the drift region 11 toward the collector 6 due to the potential gradient created by the electric field generating unit 7, and reach the collector 6. At this time, the negative or positive ions move against the flow of the drift gas. This flow of drift gas acts as a resistance for the negative or positive ions moving from the electrostatic gate electrode 8 toward the collector 6. The magnitude of this resistance (ion mobility) varies depending on the ion species. Generally, mobility is inversely proportional to the ion's collision cross-section (ion size). Therefore, the larger the ion's collision cross-section, the longer it takes for the ion to reach the collector 6. (The larger the ion, the more frequently it collides with air molecules in the drift gas, resulting in a slower migration speed and a longer arrival time at the collector 6.) Therefore, the time (arrival time, peak position) from when the ion is injected into the drift region 11 by the electrostatic gate electrode 8 to when it reaches the collector 6 varies depending on the ion species (negative or positive ion). Therefore, it is possible to identify negative or positive ions (detection target components contained in the sample) based on this arrival time (peak position). In addition, ions of multiple detection target components contained in the sample gas can be separated in the drift region 11.

[0040] The collector 6 is a metal member that collects the electric charge of negative or positive ions. The collector 6 can be electrically connected to a recovery current measuring unit 19 of the control unit 12. The recovery current measuring unit 19 is also configured to measure, in time series, the recovery current generated when negative or positive ions transfer electric charge to the collector 6. This makes it possible to measure the current waveform (IMS spectrum) of the recovery current.

[0041] Multiple types of ions injected into the drift region 11 in a single pulse using the electrostatic gate electrode 8 are separated into various ions as they move through the drift region 11, and the various ions arrive at the collector 6 with a time lag. As a result, the current waveform (IMS spectrum) of the collected current exhibits peaks corresponding to the arrival times of the various ions, and the mobility can be calculated from the peak positions (arrival times), making it possible to identify the ion components. Furthermore, since the peak heights or peak areas of the current waveform of the collected current correspond to the amount of charge transferred by the various ions to the collector 6, quantitative analysis of the target components can be performed based on the peak heights or peak areas.

[0042] Next, an IMS analysis method using the IMS analyzer 40 of this embodiment will be described. This method can be implemented by controlling the IMS analyzer 40 using the control unit 12. Here, the case where the IMS analyzer 40 is operated in negative ion mode will be described. The drift gas is air, and the carrier gas is air containing moisture. Fig. 2 is a flowchart of the IMS analysis method of this embodiment, and Fig. 3 is a graph showing an IMS spectrum (noise removed) measured by the IMS analysis method of this embodiment. The horizontal axis of this graph represents the arrival time of ions, with the moment when the electrostatic gate electrode 8 is opened set to 0, and the vertical axis represents the recovery current generated by the charge recovery of ions that have reached the collector 6.

[0043] In step S1, calibration is performed. Specifically, drift gas (air) is injected into analysis chamber 30 using drift gas injection unit 15, and carrier gas (air containing moisture) not containing sample gas is injected into analysis chamber 30 using sample gas injection unit 16. In this state, an element voltage is applied between bottom electrode 3 and surface electrode 4 of electron emitter 2 using control unit 12. Electrons emitted from electron emitter 2 attach to components contained in the air, generating negative ions (primary ions). These negative ions move to the vicinity of electrostatic gate electrode 8 due to the electric field formed in analysis chamber 30.

[0044] The electrostatic gate electrode 8 is momentarily opened to inject negative ions (primary ions) into the drift region 11 in a single pulse. The negative ions travel through the drift region 11 against the flow of the drift gas due to the electric field of the analysis chamber 30 and reach the collector 6. The charge transferred by the negative ions to the collector 6 generates a collection current, allowing an IMS spectrum to be measured. This IMS spectrum contains a first peak (RIP: Reactant Ion Peak) corresponding to the negative ions (primary ions) generated from components in the air. The peak height or peak area of ​​this first peak is compared with a preset target value. If the peak height or peak area of ​​the first peak is within ±5% of the target value, the first calibration is terminated and the process proceeds to step S2. If the peak height or peak area of ​​the first peak is outside the ±5% range of the target value, the device voltage applied between the lower electrode 3 and the surface electrode 4 of the electron-emitting device 2 is changed, and IMS analysis is performed to measure the IMS spectrum. This IMS analysis is repeated until the peak height or peak area of ​​the first peak falls within ±5% of the target value, and then the process proceeds to step S2. The peak height or peak area of ​​the first peak that appeared in the last measured IMS spectrum is calculated, and this peak height or peak area is used as the reference value. When repeating IMS analysis of the sample gas, calibration can be performed again so that the peak height or peak area of ​​the first peak approaches this reference value. By performing such calibration, the amount of primary ions produced in the ionization region 10 can be stabilized, and the components to be detected can be quantitatively measured.

[0045] In step S2, drift gas (air) is injected into analysis chamber 30 using drift gas injector 15, and a mixed gas of sample gas and carrier gas (air containing moisture) is injected into analysis chamber 30 using sample gas injector 16. While this is happening, controller 12 applies an element voltage adjusted by calibration between bottom electrode 3 and surface electrode 4 of electron emitter 2. Electrons emitted from electron emitter 2 attach to components contained in the air, generating negative ions (primary ions). These primary ions then transfer charge to the target component contained in the sample gas, generating negative ions of the target component. These negative ions move to the vicinity of electrostatic gate electrode 8 due to the electric field formed in analysis chamber 30.

[0046] When the electrostatic gate electrode 8 is momentarily opened to inject negative ions into the drift region 11 in a single pulse, the negative ions move through the drift region 11 against the flow of the drift gas due to the electric field in the analysis chamber 30 and reach the collector 6. The charge transferred by the negative ions to the collector 6 then generates a collection current, allowing an IMS spectrum to be measured. This IMS spectrum contains a first peak (RIP) corresponding to negative ions (primary ions) generated from components in the air and a peak corresponding to negative ions generated from the target component. For example, an IMS spectrum (1) such as the one shown by the solid black line in the graph in Figure 3 is measured. Multiple peaks corresponding to negative ions generated from the target component may appear in the IMS spectrum. If at least one of these peaks overlaps with the first peak, a so-called hidden peak is present.

[0047] Peak detection in an IMS spectrum can be performed, for example, as follows. (1) Electrical noise due to the response of the electrostatic gate electrode 8 is removed from the measured waveform using an approximation formula based on a first-order lag element. (2) Use a low-pass filter (cutoff = 5000 Hz) to remove high-frequency noise from the measured waveform. (3) The peak position is detected by detecting the position of the positive to negative zero crossing point in the first derivative waveform of the measured waveform. (4) The time of the negative to positive zero crossing point in the third derivative waveform of the measured waveform is determined, and the inflection point is detected by checking whether the second derivative waveform has a negative minimum value corresponding to the determined time. (5) For the obtained time, obtain a value greater than the threshold value (noise component: 3σ) set in the original (separate from the noise component). (6) Delete the overlapping points between the detected peak positions and the detected inflection points. Specifically, if there is another detected point in the vicinity (approximately 0.15 msec) of each detected point, the one with the larger value is detected as the peak, and the other one is deleted. Such a peak detection method can be used in steps S3, S5, etc.

[0048] In step S3, the control unit 12 determines whether there is a minor peak in the IMS spectrum measured in step S2. It is also possible to determine whether there is a minor peak overlapping the first peak using a method similar to step S5 described later. This makes it possible to determine whether there is a hidden peak. If it is determined that there is a minute peak, the process proceeds to step S5, and if it is determined that there is no minute peak, the process proceeds to step S4. In step S4, it is determined whether the device voltage applied between the lower electrode 3 and the surface electrode 4 of the electron emitter 2 has reached its upper limit. If it has reached the upper limit, the process proceeds to step S5. If it has not, the process returns to step S1, and steps S1 and S2 are performed again. In step S1, a target value greater than the target value set in the previous step S1 is set. This increases the device voltage applied between the lower electrode 3 and the surface electrode 4 of the electron emitter 2, increasing the amount of primary ions generated in the ionization region 10. As a result, a new minute peak appears in the IMS spectrum measured in step S2. This minute peak may become a new second peak. Furthermore, the peak intensities of the first and second peaks appearing in the IMS spectrum measured in step S2 increase. In step S2, for example, an IMS spectrum (2) such as that shown by the black dashed line in the graph of FIG. 3 is measured, and the peak intensities of the first and second peaks are greater than those of the IMS spectrum (1). For example, the device voltage applied between the lower electrode 3 and the surface electrode 4 of the electron-emitting device 2 can be increased from 10V to 12V.

[0049] In step S5, the control unit 12 determines whether or not there is a peak overlapping the vicinity of the first peak (RIP) corresponding to the primary ion in the IMS spectrum measured in the immediately preceding step S2. First, the control unit 12 determines whether or not a second peak overlaps with the first peak within a predetermined range around the first peak (for example, a range twice the half-width of the first peak). If it determines that a second peak overlaps with the first peak, the process proceeds to step S6. Next, the control unit 12 can determine whether a second peak overlaps with the first peak by comparing the IMS spectrum measured in the immediately preceding step S1 with the IMS spectrum measured in the immediately preceding step S2. For example, the control unit 12 can overlap the first peak of the IMS spectrum measured in step S1 with the first peak of the IMS spectrum measured in step S2 and extract portions with different peak shapes. For example, if there is a portion where the base shape or shoulder shape of the first peak is larger in the IMS spectrum measured in step S2, it can be determined that a second peak overlaps with the first peak. In this case, the process proceeds to step S6.

[0050] If there is almost no difference between the shape of the first peak in the IMS spectrum measured in step S1 and the shape of the first peak in the IMS spectrum measured in step S2, the controller 12 determines that there is no second peak overlapping the first peak, and ends this control flow. In this case, the IMS spectrum measured in the immediately preceding step S2 can be used as the measurement result.

[0051] In step S6, the control unit 12 sets a drift voltage that changes the potential of the electric field forming electrode so as to reduce the gradient of the potential gradient formed in the drift region 11. That is, the drift voltage is set to a voltage that is lower than the drift voltage set in the previous measurement in step S2 and higher than a preset lower limit drift voltage. For example, if a drift voltage is applied in step S2 so that the potential of the electric field forming electrode 9a of the IMS analyzer 40 shown in FIG. 1 becomes −3000 V, the drift voltage is set to a voltage that is lower than 3000 V and higher than 300 V (the lower limit voltage). This reduces the gradient of the potential gradient formed in the drift region 11. The control unit 12 can set the drift voltage with a preset change width. For example, if the change width is set to 300 V, the control unit 12 can set the drift voltage so that the potential of the electric field forming electrode 9 a becomes −2700 V.

[0052] Alternatively, the control unit 12 may calculate the variation width of the drift voltage from the difference between the position (arrival time) of the first peak and the position (arrival time) of the second peak, and set the drift voltage accordingly. This allows the drift voltage to be set appropriately. For example, if the positions of the first peak and the second peak are relatively close to each other, the variation width of the drift voltage can be increased, and if the positions of the first peak and the second peak are relatively far from each other, the variation width of the drift voltage can be decreased.

[0053] In step S7, the control unit 12 determines whether the set drift voltage is within the allowable range (whether it has reached the lower limit voltage). If the drift voltage is outside the allowable range (has reached the lower limit), this control flow ends, and the IMS spectrum measured in the immediately preceding step S2 can be used as the measurement result. If the drift voltage is within the allowable range, the process returns to step S2 and measures the sample gas. In this step S2, the gradient of the potential gradient in the drift region 11 is smaller than in the previous step S2, so the time it takes for the primary ions and ions generated from the target components to reach the collector 6 after passing through the electrostatic gate electrode 8 is longer. This increases the difference between the positions (arrival times) of the first and second peaks in the IMS spectrum, allowing the second peak to be separated from the first peak. It is confirmed that the second peak identified in the previous step S5 has been separated from the first peak, and this peak is identified. Then, step S5 is performed again to determine whether there is a new peak overlapping the first peak.

[0054] For example, the IMS spectrum (3) shown by the solid gray line in the graph in Figure 3 is measured. In the IMS spectrum (3), the first peak (RIP) and the second peak (the peak corresponding to the target substance) appear later (the arrival time is longer) than in the IMS spectrum (2). In addition, the second peak is separated from the first peak. If it is determined in step S5 that there is no peak overlapping the first peak, this control flow is terminated, and the IMS spectrum measured in the immediately preceding step S2 can be used as the measurement result.

[0055] By increasing the device voltage applied between the bottom electrode 3 and surface electrode 4 of the electron-emitting device 2 to increase detection sensitivity and make it possible to detect minute peaks, and then performing IMS analysis by reducing the drift voltage for overlapping peaks, peak separation can be improved. This makes it possible to increase detection sensitivity without reducing peak separation. In the above description of the embodiment, the first peak is a primary ion generated by ionizing the carrier gas, air, and the second peak is one of multiple detection peaks generated by ionizing the sample gas that overlaps with the first peak. However, the first peak may be a peak of the sample gas, and the method may be applied to separating overlapping peaks of the sample gas. [Explanation of symbols]

[0056] 1: ion source 2: electron emitter 3: lower electrode 4: surface electrode 5: intermediate layer 6: collector 7: electric field generating section 8: electrostatic gate electrode 9a to 9h: electric field generating electrodes 10: ionization region 11: drift region 12: control section 15: drift gas injection section 16: sample gas injection section 17: element voltage control section 19: recovery current measuring section 20: exhaust section 22: element holder 25: grid electrode 26: electric field control section 27: gate control section 28: housing 29: insulation section 30: analysis chamber 40: IMS analysis device

Claims

1. The apparatus comprises an ion source, a collector, an electrostatic gate electrode, an electric field forming electrode, a control unit, and a sample gas injection unit; the control unit is configured to control the potential of the electric field forming electrode so as to form a potential gradient in a drift region between the electrostatic gate electrode and the collector, the collector and the control unit are configured to measure a current waveform of a current that flows when ions reach the collector; the control unit is configured to determine whether or not a second peak overlapping a first peak exists in the current waveform, and when it is determined that a second peak exists, to change the potential of the electric field forming electrode so that the inclination of the potential gradient becomes smaller, and measure the current waveform; the collector, the electrostatic gate electrode, and the electric field forming electrode are contained in an analysis chamber; the sample gas injector is configured to inject a mixed gas of a sample gas and a carrier gas or a carrier gas not containing the sample gas into the analysis chamber; the ion source is configured to directly or indirectly ionize components contained in the sample gas or components contained in the carrier gas; the first peak corresponds to ions generated from a component contained in the carrier gas; the second peak corresponds to an ion generated from a component contained in the sample gas, the control unit is configured to determine whether or not a second peak exists by comparing the current waveform measured when a carrier gas not including the sample gas is being injected into the analysis chamber with the current waveform measured when the mixed gas is being injected into the analysis chamber; the ion source is an electron-emitting device, the electron-emitting element has a lower electrode, a surface electrode, and an intermediate layer disposed between the lower electrode and the surface electrode; the control unit is configured to apply a voltage between the lower electrode and the surface electrode, the carrier gas is air containing moisture, The control unit and the sample gas injection unit are configured to adjust the voltage applied between the lower electrode and the surface electrode so that the peak height or peak area of ​​the first peak approaches a target value when a carrier gas not containing the sample gas is injected into the analysis chamber, and the IMS analysis device is configured to inject the mixed gas into the analysis chamber and measure the current waveform after adjusting the voltage applied between the lower electrode and the surface electrode.

2. 2. The IMS analysis apparatus of claim 1, wherein the control unit is configured to determine whether or not a minute peak exists in the current waveform measured while the mixed gas is being injected into the analysis chamber, and when it is determined that a minute peak does not exist, to increase the voltage applied between the lower electrode and the surface electrode.

3. The apparatus comprises an ion source, a collector, an electrostatic gate electrode, an electric field forming electrode, a control unit, and a sample gas injection unit; the control unit is configured to control the potential of the electric field forming electrode so as to form a potential gradient in a drift region between the electrostatic gate electrode and the collector, the collector and the control unit are configured to measure a current waveform of a current that flows when ions reach the collector; the control unit is configured to determine whether or not a second peak overlapping a first peak exists in the current waveform, and when it is determined that a second peak exists, to change the potential of the electric field forming electrode so that the inclination of the potential gradient becomes smaller, and measure the current waveform; the collector, the electrostatic gate electrode, and the electric field forming electrode are contained in an analysis chamber; the sample gas injector is configured to inject a mixed gas of a sample gas and a carrier gas or a carrier gas not containing the sample gas into the analysis chamber; the ion source is configured to directly or indirectly ionize components contained in the sample gas or components contained in the carrier gas; the first peak corresponds to ions generated from a component contained in the carrier gas; the second peak corresponds to an ion generated from a component contained in the sample gas, the control unit is configured to determine whether or not a second peak exists by comparing the current waveform measured when a carrier gas not including the sample gas is being injected into the analysis chamber with the current waveform measured when the mixed gas is being injected into the analysis chamber; the ion source is an electron-emitting device, the electron-emitting element has a lower electrode, a surface electrode, and an intermediate layer disposed between the lower electrode and the surface electrode; the control unit is configured to apply a voltage between the lower electrode and the surface electrode, the carrier gas is air containing moisture, The control unit is configured to determine whether or not a minute peak exists in the current waveform measured when the mixed gas is injected into the analysis chamber, and if it determines that a minute peak does not exist, to increase the voltage applied between the lower electrode and the surface electrode.

4. 4. The IMS analysis apparatus according to claim 1, wherein the control unit is configured to determine whether or not a second peak exists that overlaps with the first peak within a predetermined range near the first peak.

5. A first measurement step of measuring the current waveform of a current that flows when ions generated by an ion source directly or indirectly ionizing components contained in a carrier gas that does not contain a sample gas reach a collector while the carrier gas is being injected into an analysis chamber; a second measurement step of measuring a current waveform of a current that flows when ions generated by the ion source directly or indirectly ionizing a component contained in the sample gas or a component contained in the carrier gas reach a collector while the mixed gas of the sample gas and the carrier gas is being injected into the analysis chamber; a determining step of determining whether or not a second peak overlapping the first peak exists in the current waveform measured in the second measuring step; a third measuring step of measuring a current waveform of a current that flows when ions reach the collector by changing the potential of the electric field forming electrode so that the gradient of the potential gradient in the drift region between the electrostatic gate electrode and the collector becomes smaller when it is determined that a second peak overlaps the first peak; the first peak corresponds to ions generated from a component contained in the carrier gas; the second peak corresponds to an ion generated from a component contained in the sample gas, In the determination step, the current waveform measured when a carrier gas not containing the sample gas is injected into the analysis chamber in the first measurement step is compared with the current waveform measured when the mixed gas is injected into the analysis chamber in the second measurement step to determine whether a second peak exists; the ion source is an electron-emitting device, the electron-emitting element has a lower electrode, a surface electrode, and an intermediate layer disposed between the lower electrode and the surface electrode; the carrier gas is air containing moisture, An IMS analysis method in which, in a first measurement step, a voltage applied between the lower electrode and the surface electrode is adjusted so that the peak height or peak area of ​​a first peak approaches a target value while a carrier gas not containing the sample gas is being injected into the analysis chamber, and after adjusting the voltage applied between the lower electrode and the surface electrode, in a second measurement step, the mixed gas is injected into the analysis chamber and the current waveform is measured.

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