IMS analysis device

Abstract

To provide an IMS analysis device capable of detecting even substances that are easily inhibited from ionization by moisture with high detection sensitivity.SOLUTION: An IMS analysis device includes: an analysis chamber; an electron emission element; an electrostatic gate electrode; a mesh electrode disposed between the electron emission element and the electrostatic gate electrode; a first gas injection unit provided so as to inject sample gas into the analysis chamber; and a second gas injection unit provided so as to inject gas containing moisture into the analysis chamber. The electron emission element includes a lower electrode, a surface electrode, and an intermediate layer. The analysis chamber includes a first ionization region between the electron emission element and the mesh electrode, and a second ionization region between the mesh electrode and the electrostatic gate electrode. The first gas injection unit is arranged to supply sample gas to the second ionization region, and the second gas injection unit is arranged to supply gas containing moisture to the first ionization region.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an IMS analyzer. [Background technology]

[0002] Conventional IMS analyzers use ion sources such as radioactive sources and corona discharge, and often ionize with high-energy electrons. Therefore, sample gas components are often decomposed by high-energy electrons, and many peaks (detection peaks) appear in the IMS spectrum. This makes it difficult to identify the components to be detected in IMS analysis. IMS is an abbreviation for Ion Mobility Spectrometry.

[0003] IMS analyzers that use electron emitters as ion sources are known. In such IMS analyzers, the components of a sample gas can be ionized directly or indirectly by low-energy electrons, which makes it possible to suppress the decomposition of the components of the sample gas. It is known that humidity is necessary to increase the amount of electrons emitted from such electron-emitting elements (see, for example, Patent Document 1).

[0004] IMS analyzers that use dry gases as carrier gases or drift gases are known (see, for example, Patent Document 2). Such IMS analyzers can suppress ion reactions or ion cluster formation caused by moisture, making it possible to detect various target substances. For example, acetone is a substance whose ionization efficiency decreases due to moisture when humidity is high, but even such a substance can be detected by using dry gas. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-038278 [Patent Document 2] U.S. Patent No. 5,218,203 Summary of the Invention [Problem to be solved by the invention]

[0006] In conventional IMS analysis devices that use electron emitters, reducing the amount of moisture in the gas injected into the analysis chamber to suppress the decrease in the ionization rate of the components to be detected due to moisture reduces the amount of electrons emitted by the electron emitter, thereby decreasing detection sensitivity, and vice versa, increasing the amount of moisture in the gas injected into the analysis chamber to increase the amount of electrons emitted by the electron emitter makes it impossible to detect substances whose ionization rate is reduced by moisture. The present invention has been made in view of the above circumstances, and provides an IMS analysis apparatus capable of detecting with high detection sensitivity even substances whose ionization is easily inhibited by moisture. [Means for solving the problem]

[0007] The present invention provides an IMS analysis apparatus comprising: an analysis chamber, an electron emitter, an electrostatic gate electrode, a mesh electrode arranged between the electron emitter and the electrostatic gate electrode, a first gas injection unit arranged to inject a sample gas into the analysis chamber, and a second gas injection unit arranged to inject a gas containing moisture into the analysis chamber, wherein the electron emitter has a lower electrode, a surface electrode, and an intermediate layer arranged between the lower electrode and the surface electrode, the analysis chamber has a first ionization region between the electron emitter and the mesh electrode, and a second ionization region between the mesh electrode and the electrostatic gate electrode, the first gas injection unit is arranged to supply the sample gas to the second ionization region, and the second gas injection unit is arranged to supply the gas containing moisture to the first ionization region. Effect of the Invention

[0008] The second gas injection unit is arranged to supply a gas containing moisture to the first ionization region between the electron emitter and the mesh electrode, so that the amount of electrons emitted from the electron emitter can be stably increased, and the amount of primary ions generated in the first ionization region can be stably increased. This makes it possible to stably increase the detection sensitivity of the IMS analyzer. In addition, it becomes possible to quantitatively analyze the detection target components. In addition, since a mesh electrode is provided between the first ionization region and the second ionization region, it is possible to prevent moisture from the first ionization region from flowing into the second ionization region. Therefore, by using the IMS analyzer of the present invention, it is possible to increase the ionization efficiency and detect with high detection sensitivity even for substances whose ionization is easily hindered by moisture. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view of an IMS analyzer according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic cross-sectional view of an IMS analyzer according to one embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic cross-sectional view of an IMS analyzer according to one embodiment of the present invention. [Figure 4] 4 is a graph showing a change in potential from an electron emitter to a detector in an IMS analysis apparatus (negative ion mode) according to one embodiment of the present invention. [Diagram 5] 4 is a graph showing a change in potential from an electron emitter to a detector in an IMS analysis apparatus (positive ion mode) according to one embodiment of the present invention. [Figure 6] This is an IMS spectrum measured using a conventional IMS analyzer. [Figure 7] This is an IMS spectrum measured using a conventional IMS analyzer. [Figure 8] 1 is an IMS spectrum measured by an IMS analyzer according to one embodiment of the present invention. [Figure 9] FIG. 1 is a schematic cross-sectional view of a conventional IMS analyzer. [Figure 10]1 is a graph showing a change in potential from an electron emitter to a detector in a conventional IMS analyzer (negative ion mode). [Figure 11] 1 is a graph showing a change in potential from an electron emitter to a detector in a conventional IMS analyzer (positive ion mode). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The IMS analysis apparatus of the present invention comprises an analysis chamber, an electron emitter, an electrostatic gate electrode, a mesh electrode arranged between the electron emitter and the electrostatic gate electrode, a first gas injection unit arranged to inject a sample gas into the analysis chamber, and a second gas injection unit arranged to inject a gas containing moisture into the analysis chamber, wherein the electron emitter has a lower electrode, a surface electrode, and an intermediate layer arranged between the lower electrode and the surface electrode, the analysis chamber has a first ionization region between the electron emitter and the mesh electrode, and a second ionization region between the mesh electrode and the electrostatic gate electrode, the first gas injection unit is arranged to supply the sample gas to the second ionization region, and the second gas injection unit is arranged to supply the gas containing moisture to the first ionization region.

[0011] The IMS analysis apparatus of the present invention preferably comprises an exhaust port arranged to exhaust gas from the analysis chamber, and the first and second gas injection parts and the exhaust port are preferably arranged so that the sample gas injected from the first gas injection part flows from the second ionization region to the first ionization region and is exhausted from the exhaust port together with the moisture-containing gas. Preferably, the first gas injector is provided to inject a mixed gas of a gas containing a component to be analyzed and a carrier gas into the analysis chamber, and the carrier gas is a dry gas. A second gas injector is preferably provided to inject a humidified gas into the analysis chamber and supply it to the first ionization region. The IMS analysis apparatus of the present invention preferably includes a control unit, and the control unit is preferably configured to apply voltages to the electron emitter, the mesh electrode, and the electrostatic gate electrode so that ions generated directly or indirectly by electrons emitted by the electron emitter move from the first ionization region through the mesh electrode to the second ionization region.

[0012] Preferably, the IMS analysis apparatus of the present invention further comprises a detector, a plurality of electric field forming electrodes, and a control unit, the analysis chamber having a drift region disposed between the electrostatic gate electrode and the detector, the control unit being configured to apply a voltage to the plurality of electric field forming electrodes so as to form an electric field in the drift region, and the detector and the control unit being configured to measure a current waveform of a current flowing when ions generated in the first or second ionization region pass through the drift region and reach the detector. Preferably, the IMS analysis apparatus of the present invention further comprises a third gas injector arranged to inject drift gas into the analysis chamber, the third gas injector being positioned in the drift region such that drift gas flows from the detector towards the electrostatic gate electrode.

[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 merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

[0014] 1 to 3 are schematic cross-sectional views of the IMS analyzer of this embodiment, and Fig. 9 is a schematic cross-sectional view of a conventional drift tube type IMS analyzer. The IMS analysis apparatus 40 of this embodiment includes an analysis chamber 30, an electron emitter 2, an electrostatic gate electrode 8, a mesh electrode 7 arranged between the electron emitter 2 and the electrostatic gate electrode 8, a first gas injection unit 13 arranged to inject a sample gas into the analysis chamber 30, and a second gas injection unit 14 arranged to inject a gas containing moisture into the analysis chamber 30. The electron emitter 2 has a lower electrode 3, a surface electrode 4, and an intermediate layer 5 arranged between the lower electrode 3 and the surface electrode 4. The analysis chamber 30 has a first ionization region 10 between the electron emitter 2 and the mesh electrode 7, and a second ionization region 11 between the mesh electrode 7 and the electrostatic gate electrode 8. The first gas injection unit 13 is arranged to supply the sample gas to the second ionization region 11, and the second gas injection unit 14 is arranged to supply a gas containing moisture to the first ionization region 10.

[0015] The IMS analyzer 40 is an apparatus that analyzes a sample by ion mobility spectrometry (IMS). In this embodiment, an IMS analyzer that performs analysis by drift tube type IMS will be described. The IMS analyzer 40 has a negative ion mode in which negative ions of the detection target component generated in the second ionization region 11 are moved to the detector 6 for detection, and a positive ion mode in which positive ions of the detection target component generated in the second ionization region 11 are moved to the detector 6 for detection. The negative ion mode and the positive ion mode differ in the voltages that the control unit 21 applies to the mesh electrode 7, the electrostatic gate electrode 8, the electric field forming electrode 9, etc.

[0016] The analysis chamber 30 is a chamber defined by a wall portion 28. In the analysis chamber 30, an electron emitter 2, a mesh electrode 7, an electrostatic gate electrode 8, a plurality of electric field forming electrodes 9, and a detector 6 are arranged. The capacity of the analysis chamber 30 is, for example, not less than 10 mL and not more than 1000 mL. The analysis chamber 30 comprises a first ionization region 10 , a second ionization region 11 and a drift region 12 .

[0017] The first ionization region 10 is a region for ionizing gas near the surface electrode 4 with electrons emitted from the electron emitter 2 to generate primary ions, and is a region located between the electron emitter 2 and the mesh electrode 7. The primary ions generated near the surface electrode 4 move away from the surface electrode 4 due to the potential gradient of the first ionization region 10. This makes it possible to prevent the vicinity of the surface electrode 4 from being charged, and to prevent a decrease in the amount of electrons emitted by the electron emitter 2. The second ionization region 11 is a region for generating ions of the component to be detected by primary ions transferring electric charge to the component to be detected contained in the sample gas (ion-molecule reaction), and is a region located between the mesh electrode 7 and the electrostatic gate electrode 8. The drift region 12 is a region in which ions move from the electrostatic gate electrode 8 toward the detector 6 against the flow of the drift gas, and is a region located between the electrostatic gate electrode 8 and the detector 6 .

[0018] The first gas injection unit 13 is a unit that injects a sample gas into the analysis chamber 30, and is arranged to supply the sample gas to the second ionization region 11. The first gas injection unit 13 may be arranged to inject the sample gas into the second ionization region 11. The sample gas contains a component to be analyzed and a carrier gas, and the component contained in this sample gas is ionized in the second ionization region 11. The carrier gas can be, for example, a dry gas (e.g., dry air, dry nitrogen, dry helium, etc.). The carrier gas may be a dry gas supplied from a gas cylinder, or may be a gas from which moisture has been removed by the dehumidification units 31a and 31b shown in Figures 2 and 3. This makes it possible to suppress ion reactions or ion cluster formation caused by moisture in the analysis chamber 30, and improve the ionization efficiency of the component to be analyzed. This makes it possible to increase the number of substances that can be analyzed.

[0019] The dehumidifying units 31a and 31b may, for example, remove moisture from the carrier gas by adsorbing water, or may remove moisture from the carrier gas using a chemical substance that undergoes a chemical reaction with water. The dehumidifying unit 31a is, for example, a part that includes activated carbon, and the dehumidifying unit 31b is, for example, a part that includes molecular sieves. These adsorbents can remove moisture from the clean air.

[0020] For example, the first gas injection section 13 may be configured to inject a mixed gas of a carrier gas (clean air dehumidified using dehumidifiers 31a and 31b) and a gas containing the components to be analyzed into the analysis chamber 30, as in the IMS analysis apparatus 40 shown in FIG. Furthermore, for example, the first gas injection section 13 may be configured, like the IMS analysis apparatus 40 shown in FIG. 3, to flow a carrier gas (clean air dehumidified using dehumidification sections 31a, 31b) through the thermal desorption collection tube 18 that has adsorbed the detection target components, heat the thermal desorption collection tube 18 to desorb the detection target components, and inject the carrier gas containing the detection target components into the analysis chamber 30.

[0021] The flow rate of the gas injected by the first gas injection unit 13 into the analysis chamber 30 is, for example, 10 mL / s or more. In addition, the sum of the flow rate of the gas injected by the first gas injection unit 13 into the analysis chamber 30 and the flow rate of the gas injected by the second gas injection unit 14 into the analysis chamber 30 can be set to be equal to or less than the drift gas injection flow rate. The sample gas injected into the second ionization region 11 using the first gas injection unit 13 merges with the drift gas flowing from the drift region 12, passes through the mesh electrode 7, flows into the first ionization region 10, and is exhausted from the exhaust port 20 to the outside of the chamber. By flowing the sample gas and drift gas in this manner, it is possible to prevent moisture from the first ionization region 10 from flowing into the second ionization region 11, and to suppress ion reactions or ion cluster formation caused by moisture in the second ionization region 11 and the drift region 12. This makes it possible to prevent a decrease in the ionization efficiency of the detection target components, and to increase the number of substances that can be analyzed.

[0022] The exhaust port 20 is a portion for exhausting the sample gas injected from the first gas injection unit 13 into the analysis chamber 30, the moisture-containing gas injected from the second gas injection unit 14 into the analysis chamber 30, and the drift gas injected from the third gas injection unit 15 into the analysis chamber 30 from the analysis chamber 30 to the outside of the chamber. The exhaust port 20 can be disposed in the wall 28 that defines the analysis chamber 30 and is closer to the electron emitter 2 than the mesh electrode 7. The exhaust port 20 may be disposed in the wall 28 on the side of the first ionization region 10 as in the IMS analysis device 40 shown in FIG. 1, or may be disposed in the wall 28 facing the back surface on the opposite side to the electron emission surface (front surface electrode 4) of the electron emitter 2 as in the IMS analysis device 40 shown in FIGS. 2 and 3. This allows the mixed gas of the sample gas and the drift gas to flow from the second ionization region 11 through the mesh electrode 7 to the first ionization region 10. In addition, it is possible to prevent the moisture-containing gas supplied from the second gas injection part 14 to the first ionization region 10 from flowing into the second ionization region 11. This makes it possible to prevent a decrease in the ionization efficiency of the detection target components, and to increase the number of substances that can be analyzed.

[0023] The second gas injection unit 14 is a part that injects a moisture-containing gas into the analysis chamber 30, and is arranged to supply the moisture-containing gas to the first ionization region 10. The second gas injection unit 14 may be arranged to inject the moisture-containing gas into the first ionization region 10. By supplying the moisture-containing gas to the first ionization region 10, moisture can be supplied to the intermediate layer 5, the surface electrode 4, and the vicinity thereof of the electron emitter 2. This makes it possible to stably increase the amount of electrons emitted from the electron emitter 2, and to stably increase the amount of ions generated in the first ionization region 10. The reason for this is not clear, but it is thought that moisture is involved in the reaction in which electrons emitted from the surface electrode 4 of the electron emitter 2 react with gas near the surface electrode 4 to generate ions, and moisture is involved in the formation of a conductive path in the intermediate layer 5 (a conductive path between the lower electrode 3 and the surface electrode 4).

[0024] The moisture-containing gas is a gas containing moisture, and is, for example, a gas having a relative humidity of 10% to 100%. The moisture-containing gas may also be air having a relative humidity of 10% to 100%, and is preferably air having a relative humidity of 40% to 80%. The second gas injection unit 14 may be provided to inject the gas (humidified gas) that has passed through the humidifier unit 19 into the analysis chamber 30. The humidifier unit 19 may be a part provided to humidify the gas using a headspace method. For example, the humidifier unit 19 may include a sealed container that stores water, as in the IMS analysis device 40 shown in FIG. 2. The second gas injection unit 14 may be provided to supply clean air (purge gas) to the headspace of the sealed container, and to supply the humidified gas discharged from the headspace of the sealed container by the supply of the purge gas to the analysis chamber 30. The humidifier unit 19 may also be provided to allow the purge gas to pass through water. The second gas injector 14 may be provided so as to inject into the analysis chamber 30 a gas that has passed through a filter (humidifier 19) containing water.

[0025] 1, the second gas injection unit 14 can be arranged so that the moisture-containing gas is injected toward the lower electrode 3 (or element holder) of the electron emitter 2, and the exhaust port 20 can be arranged so that the gas in the analysis chamber 30 is exhausted from the side of the first ionization region 10. In this case, the moisture-containing gas injected from the second gas injection unit 14 into the analysis chamber 30 flows from the back side of the electron emitter 2 around the side or upper part of the electron emitter 2 to the first ionization region 10, where it merges with the sample gas and drift gas flowing from the second ionization region 11, and is exhausted from the exhaust port 20 to the outside of the analysis chamber 30.

[0026] For example, as in the IMS analysis apparatus 40 shown in Fig. 2 and Fig. 3, the second gas injection part 14 can be arranged so that the moisture-containing gas is injected from the side into the first ionization region 10, and the exhaust port 20 can be arranged so that the gas between the element holder 17 and the wall part 28 is exhausted. Also, the element holder 17 can be arranged so that it contacts the inner surface of the wall part 28 in which the injection port through which the moisture-containing gas is injected from the second gas injection part 14 is arranged. In this case, the moisture-containing gas injected from the second gas injection part 14 into the analysis chamber 30 is supplied to the first ionization region 10, merges with the sample gas and drift gas flowing from the second ionization region 11 in the first ionization region 10, flows from the first ionization region 10 around the side or upper part of the electron emitter 2 to the back side of the electron emitter 2, and is exhausted from the exhaust port 20 to the outside of the analysis chamber 30.

[0027] The flow rate of the gas injected by the second gas injection unit 14 into the analysis chamber 30 is, for example, 10 mL / s or more. In addition, the sum of the flow rate of the gas injected by the first gas injection unit 13 into the analysis chamber 30 and the flow rate of the gas injected by the second gas injection unit 14 into the analysis chamber 30 can be set to be equal to or less than the drift gas injection flow rate.

[0028] The third gas injection unit 15 is a part that injects drift gas (dry gas) into the analysis chamber 30. The third gas injection unit 15 is provided so that the drift gas flows from the detector 6 side toward the electrostatic gate electrode 8 side in the drift region 12. The drift gas that flows through the drift region 12 and reaches the second ionization region 11 merges with the sample gas, passes through the mesh electrode 7, and flows into the first ionization region 10, where it merges with the moisture-containing gas and is exhausted from the exhaust port 20 to the outside of the chamber. The drift gas is, for example, dry air, dry nitrogen, dry helium, etc. The third gas injection unit 15 can be provided, for example, as in the IMS analysis device shown in Figures 1 to 3. The flow rate of the drift gas that the third gas injection unit 15 injects into the analysis chamber 30 is, for example, 10 mL / s or more and 1000 mL / s or less.

[0029] The electron emitter 2 is provided to emit electrons from the surface electrode 4, and is an element for ionizing gas in the vicinity of the electron emitter 2 (surface electrode 4) with the emitted electrons to generate primary ions (negative ions or positive ions). The electron emitter 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. The electron emitter 2 can be disposed such that the surface electrode 4 faces the first ionization region 10. This allows the primary ions generated in the vicinity of the surface electrode 4 to be stably supplied to the first ionization region 10. The electron emitter 2 may be fixed to an element holder 17. In this case, the element holder 17 to which the electron emitter 2 is fixed is fixed to a wall 28 of the analysis chamber 30. The element holder 17 may also have wiring for applying a voltage to the electron emitter 2.

[0030] 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 material of the surface electrode 4 is, for example, gold or platinum. The surface electrode 4 may also be composed of multiple metal layers. Even if the surface electrode 4 has a thickness of 40 nm or more, it may have a plurality of 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 voltage between the lower electrode 3 and the surface electrode 4.

[0031] The lower electrode 3 is an electrode facing the surface electrode 4 via the intermediate layer 5. The lower electrode 3 may be a metal plate, or a metal layer or a conductor layer formed on an insulating substrate or film. When the lower electrode 3 is made of a metal plate, this metal plate may be the substrate of the electron emitter 2. The material of the lower electrode 3 is, for example, aluminum, stainless steel, nickel, etc. The thickness of the lower electrode 3 is, for example, 200 μm or more and 1 mm or less.

[0032] The intermediate layer 5 is a layer in which electrons flow due to an electric field formed by applying a voltage between the surface electrode 4 and the lower electrode 3. The intermediate layer 5 may have semiconductivity. 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.

[0033] The surface electrode 4 and the lower electrode 3 can each be electrically connected to an element voltage control section 22 of the control section 21. The control section 21 is provided to control the magnitude of the voltage (element voltage) 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 control section 21 (the element voltage is made 0 V), no current flows through the intermediate layer 5 and no electrons are emitted from the electron-emitting element 2. When a voltage (device voltage) is applied between the lower electrode 3 and the surface electrode 4 using the control unit 21 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 from the electron emitter 2. The voltage applied between the lower electrode 3 and the surface electrode 4 to cause electrons to be emitted from the electron emitter 2 can be, for example, 5 V or more and 50 V or less.

[0034] The control unit 21 is a part that controls the IMS analyzer 40. The control unit 21 can include, for example, a microcontroller having a CPU, a memory, a timer, an input / output port, etc. The control unit 21 can also include an electric field control unit 24, a gate control unit 23, an element voltage control unit 22, a recovery current measurement unit 25, a power supply unit, etc.

[0035] When electrons are emitted from the electron emitter 2 (surface electrode 4) into gas, the electrons immediately collide with gas components to form primary ions (negative ions or positive ions). When the electrons emitted from the electron emitter 2 attach to gas components in the vicinity of 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 in the vicinity of the surface electrode 4, positive ions of the gas components are generated. Primary ions (negative ions) are, for example, O2 - And so on.

[0036] Primary ions generated near the electron emitter 2 (surface electrode 4) move in the first ionization region 10 away from the electron emitter 2 due to the electric field formed in the first ionization region 10 by the electron emitter 2 and the mesh electrode 7. This makes it possible to prevent the vicinity of the surface electrode 4 from being charged, and the amount of electrons emitted by the electron emitter 2 can be stably increased. In addition, it is preferable that the potential gradient in the first ionization region 10 is large. This makes it possible to quickly move the primary ions away from the surface electrode 4, and the amount of electrons emitted by the electron emitter 2 can be stably increased. The primary ions in the first ionization region 10 move through the mesh electrode 7 to the second ionization region 11 due to an electric field formed in the first and second ionization regions 10, 11 by the electron emitter 2, the mesh electrode 7, the electrostatic gate electrode 8, etc. The primary ions become charge transport mediators that transfer charges to the detection target components contained in the sample gas in the second ionization region 11.

[0037] The mesh electrode 7 is an electrode disposed between the electron emitter 2 and the electrostatic gate electrode 8, and separates the first ionization region 10 from the second ionization region 11. The mesh electrode 7 also has a metallic mesh. The mesh electrode 7 can have, for example, a mesh woven from metal wires and a frame surrounding the mesh. Gas in the second ionization region 11 can flow to the first ionization region 10 through the mesh of the mesh electrode 7. Furthermore, primary ions in the first ionization region 10 can move to the second ionization region 11 through the mesh of the mesh electrode 7.

[0038] In the negative ion mode, the control unit 21 can control the potential of the mesh electrode 7 so that the potential of the mesh electrode 7 is greater than the potential of the electron emitter 2 and less than the potential of the electric field forming electrode 9 on the detector 6 side closest to the electrostatic gate electrode 8. In addition, in the positive ion mode, the control unit 21 can control the potential of the mesh electrode 7 so that the potential of the mesh electrode 7 is smaller than the potential of the electron emitter 2 and larger than the potential of the electric field forming electrode 9 on the detector 6 side closest to the electrostatic gate electrode 8. By controlling the potential of the mesh electrode 7 in this manner, an electric field can be formed in the first ionization region 10, and the primary ions generated in the vicinity of the electron emitter 2 can be moved toward the mesh electrode 7. The primary ions can also move to the second ionization region 11 through the mesh of the mesh electrode 7.

[0039] The electrostatic gate electrode 8 is an electrode disposed between the second ionization region 11 and the drift region 12, and controls the injection of ions generated in the first or second ionization region 10, 11 into the drift region 12 by utilizing 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 line together with a plurality of electric field forming electrodes 9. The electrostatic gate electrode 8 can be electrically connected to a gate control unit 23 of the control unit 21. The electrostatic gate electrode 8 is provided so as to be able to change the potential gradient formed in the analysis chamber 30.

[0040] The electric field in the analysis chamber 30 is formed by controlling the potentials of the electron emitter 2, mesh electrode 7, electrostatic gate electrode 8, electric field forming electrode 9, detector 6, and the like by the control unit 21. The control unit 21 controls the potentials of the electron emitter 2, mesh electrode 7, electrostatic gate electrode 8, electric field forming electrode 9, detector 6, etc. so that a potential gradient is formed such that primary ions generated near the electron emitter 2 (surface electrode 4) move to the first ionization region 10 and then move to the second ionization region 11 through the mesh (gaps) of the mesh electrode 7. The control unit 21 also controls the potentials of the electron emitter 2, mesh electrode 7, electrostatic gate electrode 8, electric field forming electrode 9, detector 6, etc. so that a potential gradient is formed such that ions that have passed through the electrostatic gate electrode 8 move to the detector 6. The inclination of the potential gradient formed is reversed between when the detection target component contained in the sample gas is detected as negative ions (negative ion mode) and when the detection target component contained in the sample gas is detected as positive ions (positive ion mode).

[0041] 4 is a graph showing the change in potential from the electron emitter 2 to the detector 6 when detecting a detection target component in negative ion mode using the IMS analyzer 40 of this embodiment. In this graph, the potential on the vertical axis decreases from bottom to top. 5 is a graph showing the change in potential from the electron emitter 2 to the detector 6 when a detection target component is detected in positive ion mode using the IMS analysis apparatus 40 of this embodiment. In this graph, the potential on the vertical axis increases from bottom to top.

[0042] Fig. 10 is a graph showing the change in potential from the electron emitter 2 to the detector 6 when detecting a target component in negative ion mode using a conventional IMS analyzer such as that shown in Fig. 9. In this graph, the potential on the vertical axis decreases from bottom to top. Fig. 11 is a graph showing the change in potential from the electron emitter 2 to the detector 6 when detecting a target component in positive ion mode using a conventional IMS analyzer such as that shown in Fig. 9. In this graph, the potential on the vertical axis increases from bottom to top. Negative charges such as electrons and negative ions move from a lower potential to a higher potential, while positive charges such as positive ions move from a higher potential to a lower potential, resulting in such a change in potential. The potential at 0 mm on the horizontal axis of the graphs in FIGS. 4, 5, 10 and 11 is the potential of the detector, and P2 to P15 are the potentials of the electric field forming electrode 9.

[0043] Before analysis, the potential of the electrostatic gate electrode 8 is potential A, and the control unit 21 momentarily opens the electrostatic gate electrode 8 to inject ions into the drift region 12, and instantaneously changes the potential of the electrostatic gate electrode 8 from potential A to potential B. In the IMS analysis apparatus 40 of this embodiment controlled in negative ion mode, as shown in the graph of Figure 4, potential A is higher than both the mesh electrode 7 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8, and potential B is lower than both the mesh electrode 7 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8. In a conventional IMS analyzer controlled in negative ion mode, as shown in Figure 10, potential A is higher than both the electron emitter 2 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8, and potential B is lower than both the electron emitter 2 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8.

[0044] In the IMS analysis apparatus 40 of this embodiment controlled in positive ion mode, as shown in the graph of Figure 5, potential A is lower than both the mesh electrode 7 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8, and potential B is higher than both the mesh electrode 7 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8. In a conventional IMS analyzer controlled in positive ion mode, as shown in Figure 11, potential A is lower than both the electron emitter 2 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8, and potential B is higher than both the electron emitter 2 and the potential (P15) of the electric field forming electrode 9 on the side of the detector 6 closest to the electrostatic gate electrode 8.

[0045] If the potential of the electrostatic gate electrode 8 is taken as potential A, the ions generated in the ionization region can move to the electrostatic gate electrode 8 due to the potential gradient, but since there is a reverse potential gradient from the electrostatic gate electrode 8 to the electric field forming electrode P15, the ions cannot move from the electrostatic gate electrode 8 to the drift region 12. In the explanation of the control of the potential of the electrostatic gate electrode 8, the term "ion" refers to negative ions in the negative ion mode and to positive ions in the positive ion mode. If the potential of the electrostatic gate electrode 8 is set to potential B, the ions cannot move to the electrostatic gate electrode 8 due to the potential gradient. In the negative ion mode, when the control unit 21 instantaneously changes the potential of the electrostatic gate electrode 8 from potential A to potential B, the potential of the electrostatic gate electrode 8 becomes higher than that of the mesh electrode 7 (this embodiment) or the electron emitter 2 (conventional) for just an instant, and lower than the potential P15 of the electric field forming electrode 9. In the positive ion mode, when the control unit 21 instantaneously changes the potential of the electrostatic gate electrode 8 from potential A to potential B, the potential of the electrostatic gate electrode 8 becomes lower than that of the mesh electrode 7 (this embodiment) or the electron emitter 2 (conventional) for just an instant, and higher than the potential P15 of the electric field forming electrode 9. During these moments, ions from the ionization region can pass through the electrostatic gate electrode 8 and travel into the drift region 12. Thus, ions can be injected into the drift region 12 only during these short times, and ions can be injected into the drift region 12 in a single pulse.

[0046] In the conventional IMS analyzer, the electric field that moves the electrons emitted from the electron emitter 2 away from the electron emitter 2 or the electric field that moves the electrons emitted from the electron emitter 2 and the primary ions generated from the gas near the surface electrode 4 toward the electrostatic gate electrode 8 is formed by the difference between the potential of the electron emitter 2 and the potential A of the electrostatic gate electrode 8. The larger the potential gradient formed by this potential difference, the more electrons can be emitted from the electron emitter 2, and the more the amount of primary ions can be increased. This makes it possible to increase the detection sensitivity of the IMS analyzer. Therefore, in the conventional IMS analyzer, in order to increase the potential gradient of the ionization region 50, it is necessary to sufficiently increase the difference between the potential of the electron emitter 2 and the potential A of the electrostatic gate electrode 8. However, if this potential difference is sufficiently increased, the difference between the potential A and the potential B of the electrostatic gate electrode 8 (gate swing voltage) becomes large. Therefore, when the control unit instantaneously changes the potential of the electrostatic gate electrode 8 from potential A to potential B in order to inject the ions in the ionization region 50 into the drift region 12, the time during which the ions are injected into the drift region 12 becomes relatively long. This can result in broad peaks appearing in the IMS spectrum or increased noise in the IMS spectrum.

[0047] Furthermore, the control unit 21 usually uses a field effect transistor (FET) to change the potential A of the electrostatic gate electrode 8 to the potential B. However, the FET has a limit to its withstand voltage, and the gate swing voltage may not be made large enough. As a result, the potential gradient of the ionization region 50 may not be made large enough, and the amount of electrons emitted by the electron emitter 2 may not be made large enough.

[0048] In the IMS analyzer 40 of this embodiment, the mesh electrode 7 is disposed between the electron emitter 2 and the electrostatic gate electrode 8, and the potential gradient of the electric field formed in the first ionization region can be increased by increasing the potential difference between the electron emitter 2 and the mesh electrode 7. This allows the amount of electrons emitted from the electron emitter 2 to be increased, and the amount of primary ions to be increased. This allows the detection sensitivity of the IMS analyzer 40 to be increased. In addition, the potential A of the electrostatic gate electrode 8 can be set without considering the amount of electrons emitted from the electron emitter 2, and therefore the difference (gate swing voltage) between the potential A and the potential B of the electrostatic gate electrode 8 can be reduced. This allows the time during which the electrostatic gate electrode 8 opens and is injected into the drift region 12 to be shortened, and an IMS spectrum with a sharp peak can be obtained. In addition, the noise of the IMS spectrum can be reduced.

[0049] In the IMS analyzer 40 of this embodiment, the sample gas injected from the first gas injection unit 13 into the analysis chamber 30 is supplied to the second ionization region 11. When the potential of the electrostatic gate electrode 8 is set to potential A, the primary ions in the first ionization region 10 can pass through the meshes of the mesh electrode 7 due to an electric field (potential gradient) and move to the second ionization region 11. In the second ionization region 11, these primary ions transfer charge to the detection target component contained in the sample gas, and negative or positive ions of the detection target component contained in the sample gas are generated (ion-molecule reaction).

[0050] The negative or positive ions generated in the second ionization region 11 are injected into the drift region 12 in a single pulse by the control unit 21 changing the potential of the electrostatic gate electrode 8 from potential A to potential B. The negative or positive ions injected into the drift region 12 move through the drift region 12 toward the detector 6 due to the potential gradient formed in the analysis chamber 30, and reach the detector 6 through the aperture grid 16. At this time, the negative or positive ions move against the flow of the drift gas. This flow of the drift gas becomes a resistance for the negative or positive ions moving from the electrostatic gate electrode 8 toward the detector 6. The magnitude of this resistance (ion mobility) differs depending on the ion species. In general, mobility is inversely proportional to the collision cross section of the ion (size of the ion), so the larger the collision cross section of the ion, the longer it takes for the ion to reach the detector 6 (the larger the ion, the more frequently it collides with air molecules in the drift gas, the slower its movement speed, and the longer it takes to reach the detector 6). Therefore, the time (arrival time, peak position) from when the ions are injected into the drift region 12 by the electrostatic gate electrode 8 until they reach the detector 6 differs depending on the type of ion, negative or positive. Therefore, it is possible to identify the 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 12.

[0051] The detector 6 is a metal member that collects the electric charge of negative or positive ions. The detector 6 can be electrically connected to a recovery current measuring unit 25 of the control unit 21. The recovery current measuring unit 25 is provided to measure in time series the recovery current that is generated when negative or positive ions transfer electric charge to the detector 6. This makes it possible to measure the current waveform (IMS spectrum) of the recovery current.

[0052] The multiple types of ions injected into the drift region 12 in a single pulse using the electrostatic gate electrode 8 are separated into various ions while moving through the drift region 12, and the various ions arrive at the detector 6 with a time lag. As a result, the current waveform (IMS spectrum) of the collected current shows a waveform with peaks corresponding to the arrival times of the various ions, and it becomes possible to calculate the mobility from the peak position (arrival time) and distinguish the ion components. This makes it possible to detect and identify the detection target components. In addition, since the peak height or peak area of ​​the current waveform of the collected current corresponds to the amount of charge transferred by the various ions to the detector 6, it becomes possible to quantitatively analyze the detection target components based on the peak height or peak area.

[0053] This type of IMS spectrum measurement can be repeated to obtain multiple IMS spectra. This allows multiple IMS spectra to be accumulated, improving the measurement accuracy of IMS analysis. It also makes it possible to measure the change in concentration of the target component over time.

[0054] When the IMS spectrum is repeatedly measured, the control unit 21 and the electron emitter 2 can be configured to adjust (feedback control) the voltage applied between the lower electrode 3 and the surface electrode 4 so that the peak height (if multiple peaks appear in the IMS spectrum, the sum of the peak heights of the peaks) or the peak area (if multiple peaks appear in the IMS spectrum, the sum of the peak areas of the peaks) of the peaks appearing in the IMS spectrum approaches a target value. This makes it possible to stabilize the amount of primary ions produced, and quantitatively measure the detection target component.

[0055] IMS analysis experiment First, an experiment was conducted to detect acetone, which is the target component, using a conventional IMS analyzer as shown in Figure 9. The IMS analyzer was controlled in positive ion mode, and the drift gas was dry air. Figure 6 shows the IMS spectrum obtained by IMS analysis in which air containing 200 ppb of acetone (relative humidity: 55%) was injected into the analysis chamber as the sample gas. Figure 7 shows the IMS spectrum obtained by IMS analysis in which air containing 200 ppb of acetone (relative humidity: 0.5%) was injected into the analysis chamber as the sample gas. The RIP (Reactant Ion Peak) that appears in the IMS spectra of Figures 6 to 8 is a peak that appears when ions ionized from air contained in the sample gas or drift gas reach the detector, and these ions are primary ions.

[0056] The IMS spectrum in Figure 6, obtained by IMS analysis with the relative humidity of the sample gas set at 55%, shows a large RIP. Furthermore, no peaks due to acetone, the target component, could be confirmed in this IMS spectrum. In this IMS analysis, the relative humidity of the sample gas injected into the analysis chamber was high, and it is believed that moisture inhibited the ionization of acetone.

[0057] In the IMS spectrum shown in Figure 7, which was obtained by IMS analysis with the relative humidity of the sample gas set at 0.5%, the RIP from the primary ions was small, and the detection sensitivity of the IMS analyzer was reduced. This is thought to be because the gas in the analysis chamber was dry, which reduced the amount of electrons emitted by the electron emitter. In addition, a peak derived from acetone, the target component, was confirmed in this IMS spectrum. In this IMS analysis, the gas in the analysis chamber was dry, so it is believed that ions of acetone contained in the sample gas were detected. However, in this IMS analysis, the detection sensitivity of the IMS analyzer was reduced, so only a small acetone peak appeared in the IMS spectrum.

[0058] Next, an experiment was carried out to detect acetone, which is a detection target component, using an IMS analysis apparatus of the present invention as shown in FIG. The IMS analyzer was controlled in positive ion mode, and air containing 200 ppb of acetone (relative humidity: 0.5%) was injected into the analysis chamber as sample gas from the first gas injection part, air with a humidity of 80% was injected into the analysis chamber from the second gas injection part, and dry air was injected into the analysis chamber as drift gas from the third gas injection part, and then IMS analysis was performed. The IMS spectrum obtained by this IMS analysis is shown in Figure 8.

[0059] The IMS spectrum in Figure 8 shows peaks for RIP and acetone. In the IMS analysis device shown in Figure 2, the humidity of the sample gas is 0.5% and the drift gas is dry air, so it is believed that ions of acetone ionized from the sample gas were detected. In addition, air with a humidity of 80% is injected into the analysis chamber from the second gas injection part. This humidified air does not pass through the second ionization region but passes through the first ionization region and is exhausted from the exhaust port to the outside of the chamber, so it is believed that it did not hinder the ionization of acetone.

[0060] The peak heights of the RIP and acetone peaks in the IMS spectrum in Figure 8 are about four times higher than those in the IMS spectrum in Figure 7. In this IMS analysis device, air with a humidity of 80% is injected from the second gas injection part into the first ionization region, which is thought to have increased the amount of electrons emitted by the electron emitter and increased the amount of primary ions generated in the first ionization region. This is thought to have increased the amount of acetone-derived ions generated in the secondary ionization region by receiving charge from the primary ions, and therefore increased the acetone peak. Thus, it was found that the IMS analysis apparatus of the present invention can detect with high detection sensitivity even a substance such as acetone, the ionization of which is easily inhibited by moisture. [Explanation of symbols]

[0061] 2: Electron emitter 3: Lower electrode 4: Surface electrode 5: Intermediate layer 6: Detector 7: Mesh electrode 8: Electrostatic gate electrode 9: Electric field forming electrode 10: First ionization region 11: Second ionization region 12: Drift region 13: First gas injection section 14: Second gas injection section 15: Third gas injection section 16: Aperture grid 17: Element holder 18: Thermal desorption collection tube 19: Humidification section 20: Exhaust port 21: Control section 22: Element voltage control section 23: Gate control section 24: Electric field control section 25: Recovery current measurement section 28: Wall section 30: Analysis chamber 31a, 31b: Dehumidification section 40: IMS analysis device 50: Ionization region

Claims

1. the analysis chamber; an electron emitter; an electrostatic gate electrode; a mesh electrode disposed between the electron emitter and the electrostatic gate electrode; a first gas injection unit provided to inject a sample gas into the analysis chamber; and a second gas injection unit provided to inject a gas containing moisture into the analysis chamber; The electron emission element has a lower electrode, a surface electrode, and an intermediate layer disposed between the lower electrode and the surface electrode, the analysis chamber having a first ionization region between the electron emitter and the mesh electrode, and a second ionization region between the mesh electrode and the electrostatic gate electrode; the first gas injector is positioned to supply a sample gas to the second ionization region; The second gas injector is arranged to supply a gas containing moisture to the first ionization region.

2. an exhaust port configured to exhaust gas from the analysis chamber; 2. The IMS analysis apparatus of claim 1, wherein the first and second gas injection sections and the exhaust port are arranged so that the sample gas injected from the first gas injection section flows from the second ionization region to the first ionization region and is exhausted from the exhaust port together with the moisture-containing gas.

3. 3. The IMS analysis apparatus according to claim 1, wherein the first gas injector is provided to inject a mixed gas of a gas containing a component to be analyzed and a carrier gas into the analysis chamber, the carrier gas being a dry gas.

4. 3. An IMS analysis apparatus as claimed in claim 1 or 2, wherein a second gas injector is provided to inject a humidified gas into the analysis chamber and supply it to the first ionization region.

5. A control unit is further provided.

3. The IMS analysis apparatus according to claim 1, wherein the control unit is configured to apply voltages to the electron emitter, the mesh electrode, and the electrostatic gate electrode so that ions generated directly or indirectly by electrons emitted by the electron emitter move from a first ionization region through the mesh electrode to a second ionization region.

6. Further comprising a detector, a plurality of electric field forming electrodes, and a control unit; the analysis chamber having a drift region disposed between the electrostatic gate electrode and the detector; the control unit is configured to apply voltages to a plurality of electric field forming electrodes so that an electric field is formed in the drift region; 3. The IMS analysis apparatus according to claim 1, wherein the detector and the control unit are configured to measure a current waveform of a current that flows when ions generated in the first or second ionization region pass through the drift region and reach the detector.

7. a third gas injector configured to inject a drift gas into the analysis chamber; 7. An IMS spectrometer as claimed in claim 6, wherein a third gas injector is positioned in said drift region such that drift gas flows from said detector towards said electrostatic gate electrode.

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