Ion source, mass spectrometer, and method for manufacturing ion source

What is AI technical title?
AI technical title is built by Patsnap AI team. It summarizes the technical point description of the patent document.
The ion source design with a conical inner cylindrical electrode and controlled voltage application addresses creeping discharges, enhancing durability and sensitivity in mass spectrometers by optimizing electric field concentration and ionization efficiency.

JP7780410B2Active Publication Date: 2025-12-04HITACHI HIGH TECH SOLUTIONS CORP

View PDF 7 Cites 0 Cited by

Patent Information

Application Number: JP2022151737
Authority / Receiving Office: JP · JP
Patent Type: Patents
Current Assignee / Owner
Filing Date: 2022-09-22
Publication Date: 2025-12-04
Estimated Expiration: 2042-09-22

AI Technical Summary

Technical Problem

Conventional dielectric barrier discharge ion sources suffer from issues such as inner wall contamination and condensation, leading to creeping discharges that inhibit plasma generation and reduce mass spectrometer sensitivity.

Method used

A dielectric barrier discharge ion source design with a conical inner cylindrical electrode and specific voltage application configurations to prevent creeping discharges, enhancing durability and ionization efficiency.

Benefits of technology

The design improves robustness and ionization efficiency, allowing for sensitive analysis of trace amounts of sample molecules by reducing the likelihood of creeping discharges and optimizing electric field concentration.

✦ Generated by Eureka AI based on patent content.

Smart Images

Figure 0007780410000001
Figure 0007780410000002
Figure 0007780410000003

Patent Text Reader

Abstract

To improve the robustness.SOLUTION: An ion source includes a tubular dielectric 121 to which a discharge gas and a sample are introduced, an outer cylindrical electrode 122 disposed in close contact with an outer side of the dielectric 121, to which a high-frequency voltage is applied, an inner cylindrical electrode 110 disposed in close contact with the dielectric 121 inside the dielectric 121, to which DC voltage is applied, and an orifice electrode 130 with an orifice 131 open to extract ions generated by discharge between the outer cylindrical electrode 122 and the inner cylindrical electrode 110 out of the dielectric 121. The inner cylindrical electrode 110 is open at both ends, has one end connected to the orifice electrode 130, includes a capillary side opening part 112 corresponding to an opening part on the side opposite to the orifice electrode side, and includes an orifice side opening part 113 corresponding to an opening part different from the capillary side opening part 112. The capillary side opening part 112 has an outer diameter less than that of the orifice side opening part 113.SELECTED DRAWING: Figure 2

Need to check novelty before this filing date? Find Prior Art

Description

[Technical Field]

[0001] The present invention relates to an ion source, a mass spectrometer, and a method for manufacturing an ion source. [Background technology]

[0002] Dielectric barrier discharge ion sources are known as ion sources that ionize gaseous chemical substances. In a dielectric barrier discharge ion source, plasma is first generated by applying an AC voltage to two electrodes shielded by a dielectric such as glass. This plasma generates ions of the gas (discharge gas) inside the ion source (primary ions). These primary ions react with sample molecules introduced into the ion source to generate ions of the sample (secondary ions).

[0003] In a conventional dielectric barrier discharge ion source, a ring-shaped outer cylindrical electrode is provided on the outside of a cylindrical dielectric body, and a cylindrical inner cylindrical electrode is provided inside the dielectric body so as to be in contact with the dielectric body. The inside of the dielectric body is kept at low pressure, and a high-frequency voltage is applied to the outer cylindrical electrode and a DC voltage is applied to the inner cylindrical electrode, generating a dielectric barrier discharge between the outer cylindrical electrode and the inner cylindrical electrode. Primary ions are generated by the plasma generated by this dielectric barrier discharge, and these primary ions react with gaseous sample molecules, ionizing the sample molecules.

[0004] Patent Document 1 discloses a mass spectrometer comprising: "a first electrode, a second electrode; a dielectric section provided between the first and second electrodes and having an inlet and outlet section for a sample and a discharge gas; a power supply that applies an AC voltage to either the first or second electrode and ionizes the sample by a discharge generated between the first and second electrodes; and a mass analysis section that analyzes ions discharged from the discharge section, wherein the discharge is performed at a pressure of 2 Torr or more and 300 Torr or less" (see claim 1).

[0005] Patent Document 2 discloses a mass spectrometer and a mass spectrometric method characterized by "having a sample placement member for placing a sample, an ionization chamber equipped with an inlet for the sample placement member and an ion source for generating sample ions, a vacuum chamber having a mass analysis unit for analyzing the sample ions, and an opening / closing mechanism provided between the ionization chamber and the vacuum chamber, wherein the opening / closing mechanism is controlled to change from a closed state to an open state after the sample placement member is introduced into the ionization chamber" (see abstract).

[0006] Patent Document 3 discloses an ionization method, an ionization device, and a mass spectrometer, characterized in that "a method for ionizing a gaseous sample, comprising the steps of: (A) reducing the pressure in an ionization chamber equipped with a plasma discharge unit and introducing the sample and atmospheric air; and (B) adjusting the pressure in the ionization chamber and generating plasma in the plasma discharge unit, wherein the plasma generated in step (B) generates [M]+ (M is the sample molecule to be measured) ions resulting from ionization of the sample and [nM+K]+ ions (n is 1 or 2, K is the adduct ion derived from the atmospheric component) resulting from the addition of ions derived from atmospheric components, and the pressure in the ionization chamber is set so that the signal intensity of the [nM+K]+ ions is greater than the signal intensity of the [M]+ ions" (see abstract).

[0007] Patent document 4 describes a plasma generating unit consisting of a glass tube, an internal electrode placed inside the glass tube to which a high voltage is applied, and a grounded electrode placed outside the glass tube and grounded (see FIG. 3D).

[0008] Furthermore, Non-Patent Document 1 describes an ion source that includes a ceramic tube, an electrode disposed outside the ceramic tube and to which a high voltage is applied, and an orifice electrode, and that discharges in a reduced pressure section. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5622751 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-8606 [Patent Document 3] Japanese Patent Application Publication No. 2018-206759 [Patent Document 4] US Patent Application Publication No. 2017 / 0354453 [Non-patent literature]

[0010] [Non-Patent Document 1] “Low-pressure barrier discharge ion source using air as a carrier gas and its application to the analysis of drugs and explosives”, Dilshadbek T. Usmanov, Zhan Yu, Lee Chuin Chen, Kenzo Hiraoka and Shinichi Yamabe, Journal of Mass Spectrometry, vol. 51, p. 132, 2016. Summary of the Invention [Problem to be solved by the invention]

[0011] In conventional dielectric barrier discharge ion sources, the inner wall surface of the dielectric may become dirty after long-term use, or condensation may form on the inner wall surface of the dielectric due to insufficient heating of the ion source. In such a state, a so-called creeping discharge may occur, which is a short circuit between the outer and inner cylindrical electrodes via the inner wall surface of the dielectric. When a creeping discharge occurs, a dielectric barrier discharge does not occur, and no plasma is generated. Consequently, sample molecules are not ionized, and the sensitivity of the mass spectrometer decreases.

[0012] The present invention has been made in view of the above background, and an object of the present invention is to improve robustness. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, the present invention provides a cylindrical dielectric into which a discharge gas and a sample are introduced, an outer cylindrical electrode that is placed so as to be in close contact with the outside of the dielectric and to which one of an AC voltage having a predetermined frequency and a DC voltage is applied, an inner cylindrical electrode that is placed inside the dielectric so as to be in close contact with the dielectric and to which the other of the AC voltage and the DC voltage is applied, and an orifice electrode that has an orifice for drawing ions generated by discharge between the outer cylindrical electrode and the inner cylindrical electrode to the outside of the dielectric, wherein the inner cylindrical electrode is open at both ends, and one end is connected to the orifice electrode, and has a first opening that is an opening on the opposite side to the orifice electrode side, and a second opening that is an opening separate from the first opening, and the outer diameter of the first opening is smaller than the outer diameter of the second opening. Other solutions will be described as appropriate in the embodiments. [Effects of the Invention]

[0014] According to the present invention, robustness can be improved. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing the configuration of a mass spectrometer according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the configuration of an ion source according to the present embodiment. [Figure 3] FIG. 10 is a diagram showing a mass spectrometer in a comparative example. [Figure 4] FIG. 10 is a diagram showing an ion source in a comparative example. [Figure 5] 4A and 4B are diagrams showing details of a conical inner cylindrical electrode in this embodiment. [Figure 6] 1A to 1C are diagrams (part 1) illustrating a method for manufacturing an ion source according to the present embodiment. [Figure 7] 10A to 10C are diagrams (part 2) illustrating the method for manufacturing an ion source according to the present embodiment. [Figure 8] 10A to 10C are diagrams (part 3) illustrating the method for manufacturing an ion source according to the present embodiment. [Figure 9] FIG. 10 is a cross-sectional view (part 1) of an inner cylindrical electrode in the first modified example. [Figure 10] FIG. 10 is a cross-sectional view (part 2) of the inner cylindrical electrode in the first modified example. [Figure 11] FIG. 10 is a cross-sectional view (part 1) of an inner cylindrical electrode in a second modified example. [Figure 12] FIG. 10 is a cross-sectional view (part 2) of the inner cylindrical electrode in the second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0016] Next, modes for carrying out the present invention (referred to as "embodiments") will be described in detail with reference to the drawings as appropriate.

[0017] (Mass spectrometer 1) Fig. 1 is a diagram showing the configuration of a mass spectrometer 1 according to this embodiment, and Fig. 2 is a diagram showing the configuration of an ion source 100 according to this embodiment. 1, the mass spectrometer 1 has an ion source 100 and a mass analysis section 200. Secondary ions are generated from sample molecules (sample) introduced into the ion source 100. The mass analysis section 200 performs mass analysis on the secondary ions generated in the ion source 100. In this embodiment, a dielectric barrier discharge ion source that discharges in a reduced pressure section is used as the ion source 100. By using a dielectric barrier discharge ion source, the pressure difference between the ion source 100 and the mass analysis section 200 is smaller than in an atmospheric pressure ion source. This allows the vacuum pumping system to be made smaller, and ultimately makes it possible to make the mass spectrometer 1 smaller.

[0018] (ion source 100) The ion source 100 (dielectric barrier discharge ion source) shown in FIG. 1 includes a cylindrical dielectric 121, such as a glass tube, into which a discharge gas and a sample are introduced. The inside of the dielectric 121 serves as the aforementioned pressure reduction section. The ion source 100 also includes a ring-shaped outer cylindrical electrode 122 that is disposed in close contact with the outside of the dielectric 121. The ion source 100 also includes an inner cylindrical electrode 110 that is disposed in close contact with the dielectric 121 inside the dielectric 121. The ion source 100 also includes an orifice electrode 130 with an orifice 131 that allows ions (secondary ions, described below) generated by a discharge (described below) between the outer cylindrical electrode 122 and the inner cylindrical electrode 110 to be drawn out of the dielectric 121. A heating section 141 is provided outside the dielectric 121. A capillary 151 for introducing sample molecules (sample) is connected to the ion source 100. The inside of the dielectric 12 is in a substantially sealed state, with no exchange of material occurring other than through the orifice 131 and the capillary 151 .

[0019] An orifice electrode 130 with an orifice 131 of about 0.2 mm to 0.5 mm is provided at the end of the dielectric 121 opposite to the end connected to the capillary 151. The inner cylindrical electrode 110 and the orifice electrode 130 are electrically connected and both are connected to a first DC power source DC1. With this configuration, an AC voltage is applied to the inner cylindrical electrode 110. The outer cylindrical electrode 122 is connected to a high-frequency power source AC.

[0020] Furthermore, a high-frequency voltage, that is, a high-frequency AC voltage having a predetermined frequency, is applied to the outer cylindrical electrode 122 by the high-frequency power supply AC. As a result, a dielectric barrier discharge occurs between the outer cylindrical electrode 122 and the inner cylindrical electrode 110, generating plasma P. The high-frequency voltage applied to the outer cylindrical electrode 122 by the high-frequency power supply AC is an AC voltage of about 10 kHz. The plasma P ionizes the gas (discharge gas) inside the ion source 100, generating primary ions. The primary ions generated by this plasma P react with sample molecules introduced into the dielectric 121 through the capillary 151, generating ions of the sample molecules (secondary ions).

[0021] The discharge gas and gaseous sample molecules for generating the plasma P are supplied to the ion source 100 via a capillary 151 .

[0022] The inside of the dielectric 121 is connected to the first chamber R1 of the mass analysis unit 200 via an orifice 131. The inside of the dielectric 121 is evacuated (arrow A1) by a roughing pump (not shown) that evacuates the first chamber R1 via the orifice 131, and therefore the pressure inside the dielectric 121 is lower than atmospheric pressure. The pressure inside the dielectric 121 is determined by the balance between the flow rate of the gas introduced via the capillary 151 and the flow rate of the gas exhausted via the orifice 131.

[0023] (Mass spectrometry department 200) The mass analysis section 200 has a first chamber R1, a second chamber R2, and a third chamber R3. The first chamber R1 is separated by an orifice electrode 130 and an apertured electrode 210. The second chamber R2 is separated by an apertured electrode 210 and an apertured electrode 230. The third chamber R3 is provided downstream of the apertured electrode 230. In this embodiment, the side of the ion source 100 is referred to as the upstream side, and the opposite side is referred to as the downstream side.

[0024] The second chamber R2 is provided with an ion guide 221. The third chamber R3 is provided with an in-cap electrode 240, a linear ion trap 250, a helium inlet tube 261, an end-cap electrode 271, and an ion detector 281.

[0025] As described above, the space between the apertured electrode 210, where the aperture 211 is open, and the orifice electrode 130 (first chamber R1) is evacuated (arrow A1) by a roughing pump (not shown). Therefore, the pressure is reduced to approximately 1 / 200 to 1 / 300 atmospheres. The internal pressure inside the dielectric 121, which is in electrical communication with the first chamber R1 via the orifice 131, is reduced to approximately 1 / 10 to 1 / 100 atmospheres. As described above, the inside of the dielectric 121 is in electrical communication with the first chamber R1. However, due to the extremely small diameter of the orifice 131 and the presence of sample molecules and the like introduced from the capillary 151, the pressure inside the dielectric 121 is slightly higher than that of the first chamber R1. Since the internal pressure inside the dielectric 121 is reduced to approximately 1 / 10 to 1 / 100 atmospheres, a dielectric barrier discharge is likely to occur.

[0026] Ions (secondary ions) of sample molecules generated in the ion source 100 flow into the first chamber R1 through the orifice 131 due to the gas flow inside the ion source 100. As described above, the first DC power supply DC1 is connected to the orifice electrode 130, and a DC voltage is applied to the orifice electrode 130. Furthermore, the second DC power supply DC2 is connected to the aperture electrode 210, and a DC voltage is applied to the aperture electrode 210. The secondary ions introduced into the first chamber R1 drift toward the aperture electrode 210 due to the potential difference between the orifice electrode 130 and the aperture electrode 210. As a result, the secondary ions are introduced from the aperture 211 into the second chamber R2, in which an ion guide 221 for focusing the secondary ions is disposed.

[0027] In the second chamber R2, the secondary ions focused by the ion guide 221 are further introduced into the third chamber R3 through an aperture 231 provided in the apertured electrode 230. A third DC power supply DC3 is connected to the apertured electrode 230, and a DC voltage is applied thereto. There are various types of mass spectrometers 1, but in this embodiment, a linear ion trap 250 type mass spectrometer 1 is described as an example. However, a mass spectrometer 1 other than the linear ion trap 250 type may also be used. The secondary ions introduced into the third chamber R3 are introduced into the linear ion trap 250 through an in-cap opening 241 opened in the in-cap electrode 240.

[0028] Dilute helium gas is introduced into the linear ion trap 250 through a helium inlet tube 261. A radio-frequency voltage is applied to each of the four rods constituting the linear ion trap 250 by a radio-frequency power supply (not shown). Secondary ions introduced into the linear ion trap 250 lose energy through collisions with the helium gas introduced through the helium inlet tube 261. As a result, the secondary ions are trapped in the electric field formed by the linear ion trap 250 and the end cap electrodes 271. The trajectories of the secondary ions trapped in the linear ion trap 250 become unstable depending on the mass-to-charge ratio of the secondary ions due to changes in the amplitude of the radio-frequency voltage applied to the rods constituting the linear ion trap 250. As a result, the secondary ions are ejected from rod openings 251 provided in the rods constituting the linear ion trap 250. The secondary ions ejected from the linear ion trap 250 are detected by an ion detector 281.

[0029] The second chamber R2 and the third chamber R3 are also evacuated (arrows A2 and A3) by vacuum pumps (not shown) to the desired pressure. A fourth DC power supply DC4 is connected to the in-cap electrode 240, and a DC voltage is applied to the in-cap electrode 240. A fifth DC power supply DC5 is connected to the end-cap electrode 271, and a DC voltage is applied to the end-cap electrode 271.

[0030] (Details of the ion source 100) Returning to the description of the ion source 100 . Capillary 151 has an inner diameter of about 0.1 mm to 0.2 mm and a length of about 10 mm to 100 mm. Gaseous sample molecules are introduced into dielectric 121 made of glass or the like through capillary 151. Capillary 151 and heating unit 141 are heated to about 200°C.

[0031] As shown in FIG. 2, the inner cylindrical electrode 110 is open at both ends, and one end is connected to the orifice electrode 130. One end is an opening on the capillary 151 side (opposite the orifice electrode side) and is a capillary-side opening 112, which is a first opening. The other end is an opening on the orifice electrode 130 (orifice 131) side and is an opening separate from the capillary-side opening 112, which is a second opening, an orifice-side opening 113. Both the inner and outer diameters of the inner cylindrical electrode 110 taper conically toward the tip (the shape of the inner cylindrical electrode 110 has a continuously deforming conical shape). Note that the tip of the inner cylindrical electrode 110 refers to the capillary-side end. That is, the outer diameter of the capillary side opening 112 is smaller than the outer diameter of the orifice side opening 113, and the inner diameter of the capillary side opening 112 is smaller than the inner diameter of the orifice side opening 113. Furthermore, sample molecules, primary ions, and secondary ions are introduced into the inner cylindrical electrode 110 from the capillary side opening 112. When the inner diameter of the dielectric 121 is 2 mm to 3 mm, the inner diameter of the capillary side opening 112 is preferably about 0.3 mm to 1 mm.

[0032] When a high-frequency voltage of approximately ±1 kV to ±2 kV at 10 kHz to 20 kHz is applied to the outer cylindrical electrode 122, a dielectric barrier discharge occurs between the outer cylindrical electrode 122 and the inner cylindrical electrode 110. This dielectric barrier discharge generates plasma P (see FIG. 1). Taking the case of measuring positive ions as an example, the voltage of the inner cylindrical electrode 110 is maintained at approximately 20 V to 30 V by the first DC power supply DC1. The ionization region F in FIG. 1 and "a" and "b" in FIG. 2 will be described later.

[0033] In this embodiment, a high-frequency voltage is applied to the outer cylindrical electrode 122 and a DC voltage is applied to the inner cylindrical electrode 110, but the reverse is also possible. That is, a DC voltage may be applied to the outer cylindrical electrode 122 and a high-frequency voltage may be applied to the inner cylindrical electrode 110. In other words, it is sufficient that one of a high-frequency voltage and a DC voltage is applied to the outer cylindrical electrode 122 and the other of a high-frequency voltage and a DC voltage is applied to the inner cylindrical electrode 110. However, when a DC voltage is applied to the outer cylindrical electrode 122 and a high-frequency voltage is applied to the inner cylindrical electrode 110, a DC voltage is applied to the orifice electrode 130, and the inner cylindrical electrode 110 and the orifice electrode 130 are insulated from each other.

[0034] [Comparative Example] Here, as a comparative example, an ion source 100z used in a conventional mass spectrometer 1z will be described with reference to FIGS. FIG. 3 is a diagram showing a mass spectrometer 1z in a comparative example, and FIG. 4 is a diagram showing an ion source 100z in a comparative example. 3 and 4 differ from the ion source 100 shown in Fig. 1 in that the inner cylindrical electrode 110z has a cylindrical shape. In Fig. 3, other than the configuration of the inner cylindrical electrode 110z, the components are the same as those in Fig. 1, and therefore the same reference numerals as in Fig. 1 are used and the description thereof will be omitted. When the ion source 100z is used for a long period of time, the inner wall surface of the dielectric 121 may become dirty, or condensation may occur on the inner wall surface of the dielectric 121 due to insufficient heating by the heating unit 141. In such a situation, a short circuit may occur between the outer cylindrical electrode 122 and the inner cylindrical electrode 110z via the inner wall surface of the dielectric 121, that is, a so-called creeping discharge may occur.

[0035] In FIG. 4, the path of the creeping discharge C is schematically indicated by a double-headed arrow. Because the voltage applied to the outer cylindrical electrode 122 is a high-frequency (AC) voltage, the creeping discharge C occurs in the direction from the inner cylindrical electrode 110z to the outer cylindrical electrode 122 and from the outer cylindrical electrode 122 to the inner cylindrical electrode 110z. When the creeping discharge C does not occur, a high-frequency voltage is applied to the outer cylindrical electrode 122 and a DC voltage is applied to the inner cylindrical electrode 110z, generating plasma P near the capillary side of the capillary-side opening 112z, as shown in FIG. 3. However, when the creeping discharge C occurs, plasma P is not generated inside the dielectric 121, and thus sample molecules are not ionized. In other words, the creeping discharge C shorts out the inner cylindrical electrode 110z and the outer cylindrical electrode 122, and no electric field is generated inside the dielectric 121. Therefore, it becomes difficult for a dielectric barrier discharge to occur between the inner cylindrical electrode 110z and the outer cylindrical electrode 122, and the generation of plasma P is inhibited.

[0036] When a creeping discharge C shown in FIG. 4 occurs, cleaning or replacement of components constituting the ion source 100z, such as the dielectric 121, is required. Furthermore, to analyze trace amounts of sample molecules with high sensitivity, the ionization efficiency of the sample molecules must be improved. In the ion source 100z shown in FIGS. 3 and 4, the capillary-side opening 112z of the inner cylindrical electrode 110z is larger than the capillary-side opening 112 of the inner cylindrical electrode 110 shown in FIG. 2, as shown in FIG. 4. Generally, the larger the diameter of the capillary-side openings 112, 112z of the inner cylindrical electrodes 110, 110z, the more the electric field generated by the high-frequency voltage applied to the outer cylindrical electrode 122 penetrates into the inner cylindrical electrodes 110, 110z. Therefore, in the ion source 100z shown in FIGS. 3 and 4, the electric field generated by the high-frequency voltage applied to the outer cylindrical electrode 122 penetrates into the inner cylindrical electrode 110z. The primary ions generated by the plasma P are expelled from the inside of the inner cylindrical electrode 110z due to the influence of the electric field penetrating into the inside of the inner cylindrical electrode 110z. Therefore, in the ion source 100z shown in Figures 3 and 4, the frequency of collisions between the primary ions and the sample molecules decreases, resulting in a phenomenon in which the ionization of the sample molecules does not progress sufficiently.

[0037] The "a=b" in FIG. 4 will be explained later.

[0038] (Comparison between the ion source 100 of this embodiment and the ion source 100z of the comparative example) As described above, in the ion source 100 shown in FIGS. 1 and 2, the outer and inner diameters of the capillary-side opening 112 are smaller than those of the orifice-side opening 113. Therefore, an electric field is concentrated near the tip of the inner cylindrical electrode 110, and a dielectric barrier discharge can be generated even if a low-frequency voltage is applied to the outer cylindrical electrode 122, compared to when the inner cylindrical electrode 110 is cylindrical as shown in FIG. 3. In other words, the electric field is concentrated at the tip of the inner cylindrical electrode 110, making it easier to generate a dielectric barrier discharge between the outer cylindrical electrode 122 and the inner cylindrical electrode 110. In other words, a dielectric barrier discharge can be generated even if the potential difference between the outer cylindrical electrode 122 and the inner cylindrical electrode 110 is low. As a result, a dielectric barrier discharge can be generated even if the high-frequency voltage applied to the outer cylindrical electrode 122 is lower than that of the ion source 100z shown in FIGS. 3 and 4. For example, in the case of a cylindrical inner cylindrical electrode 110z as shown in Fig. 3, when a dielectric barrier discharge is generated, a high-frequency voltage of ±1.5 kV is applied to the outer cylindrical electrode 122. In contrast, when the tip of the inner cylindrical electrode 110 is tapered (conical) as shown in Fig. 1, a dielectric barrier discharge can be generated with a high-frequency voltage of about ±1.2 kV to the outer cylindrical electrode 122. Thus, compared to the cylindrical inner cylindrical electrode 110z as shown in Fig. 3, the conical inner cylindrical electrode 110 as shown in Fig. 1 makes it possible to generate a dielectric barrier discharge with a lower applied voltage.

[0039] 1 and 2, when the high-frequency voltage applied to the outer cylindrical electrode 122 is reduced, creeping discharge, in which a current flows along the inner wall surface of the dielectric 121, can be prevented. That is, when the high-frequency voltage applied to the outer cylindrical electrode 122 is reduced, the potential difference between the outer cylindrical electrode 122 and the inner cylindrical electrode 110 is reduced, making it difficult for creeping discharge to occur. This improves the durability (robustness) of the ion source 100.

[0040] In the ion source 100 shown in FIGS. 1 and 2, the inside of the inner cylindrical electrode 110 is surrounded by conductors of the same potential, and therefore no electric field is generated. Also, as shown in FIG. 2, the capillary-side opening 112 of the inner cylindrical electrode 110 is smaller than the capillary-side opening 112z of the inner cylindrical electrode 110z shown in FIG. 4. This makes it difficult for the electric field generated near the outer cylindrical electrode 122 and the tip of the inner cylindrical electrode 110 to penetrate into the inside of the inner cylindrical electrode 110. As described above, the electric field generated between the outer cylindrical electrode 122 and the inner cylindrical electrode 110 penetrates into the inner side of the inner cylindrical electrode 110 depending on the diameter of the capillary-side opening 112 of the inner cylindrical electrode 110. For example, if the diameter of the capillary-side opening 112 of the inner cylindrical electrode 110 is 3 mm, the electric field penetrates approximately 3 mm from the capillary-side opening 112.

[0041] Because the inside of the inner cylindrical electrode 110 is surrounded by a conductor of the same potential and the capillary-side opening 112 of the inner cylindrical electrode 110 is small, there is almost no electric field inside the inner cylindrical electrode 110. Therefore, primary ions remain inside the inner cylindrical electrode 110 without drifting due to the electric field. Therefore, primary ions and sample molecules that have not been ionized by the plasma P near the tip of the inner cylindrical electrode 110 repeatedly collide for a sufficient period of time inside the inner cylindrical electrode 110 (ionization region F in Figure 1). As a result, ionization of the sample molecules is promoted. This improves the ionization efficiency of the sample molecules, making it possible to realize a highly sensitive mass spectrometer 1. Secondary ions generated by the plasma P near the tip of the inner cylindrical electrode 110 are also introduced inside the inner cylindrical electrode 110.

[0042] The inner diameter of the capillary-side opening 112 of the inner cylindrical electrode 110 is preferably larger than the inner diameter of the orifice 131. This ensures sufficient time for the primary ions and sample molecules to react with each other in the ionization region F inside the inner cylindrical electrode 110 shown in Figures 1 and 2. If the inner diameter of the orifice 131 is larger than the inner diameter of the capillary-side opening 112 of the inner cylindrical electrode 110, the primary ions and sample molecules present in the ionization region F will be quickly exhausted through the orifice 131 toward the first chamber R1. As a result, the ionization of the sample molecules will not proceed sufficiently.

[0043] Incidentally, in the technology described in Non-Patent Document 1, the orifice electrode 130 itself is bent toward the dielectric 121, thereby forming a conical shape. However, in the technology described in Non-Patent Document 1, the capillary-side opening 112 of this embodiment also serves as the orifice 131. Therefore, in the technology described in Non-Patent Document 1, the inside of the conical shape becomes part of the first chamber R1. Therefore, the technology described in Non-Patent Document 1 does not form the ionization region F as in this embodiment, and therefore cannot improve the ionization efficiency of sample molecules.

[0044] As described above, secondary ions present inside the inner cylindrical electrode 110 (ionization region F) are introduced into the first chamber R1 through the orifice 131 by the flow of gas. A voltage of approximately 5 V to 10 V is applied to the apertured electrode 210, which opens into the aperture 211, and the secondary ions introduced into the first chamber R1 drift toward the aperture 211 due to the electric field. The process of mass analyzing the ions (secondary ions) of sample molecules has been described above. Note that when measuring negative ions, the polarity of the DC voltage is reversed, and a DC voltage of approximately −20 V to −30 V is applied to the orifice electrode 130, and a DC voltage of approximately −5 V to −10 V is applied to the apertured electrode 210.

[0045] As shown in Fig. 2, let the electrode distance (the first distance) between the tip of the inner cylinder electrode 110 (the capillary side opening 112) and the side end of the orifice electrode 130 of the outer cylinder electrode 122 (the orifice electrode side end) be a. Also, let the distance between the location where the inner cylinder electrode 110 contacts the inner wall of the dielectric 121 and the side end of the orifice electrode 130 of the outer cylinder electrode 122 (the orifice electrode side end) be the creeping distance (the second distance: b). In this case, for the inner cylinder electrode 110 shown in Figs. 1 and 2, as shown in Fig. 2, a < b (the first distance is less than the second distance). As shown in Fig. 4, in the ion source 100z of the comparative example, a = b. That is, as shown in Fig. 2, in the ion source 100 of the present embodiment, the creeping distance (b) of the inner cylinder electrode 110 is longer than that of the cylindrical inner cylinder electrode 110 shown in Figs. 3 and 4. As the creeping distance (b) increases, the potential difference between the outer cylinder electrode 122 and the inner cylinder electrode 110 required for the occurrence of the creeping discharge C (see Fig. 4) increases. That is, even if the voltage of the high-frequency voltage applied to the outer cylinder electrode 122 in the ion source 100 of the present embodiment is equal to that of the ion source 100z shown in Figs. 3 and 4, the creeping discharge is less likely to occur due to the increase in the creeping distance (b). As described above, by making the inner cylinder electrode 110 conical, the voltage of the high-frequency voltage applied to the outer cylinder electrode 122 can be lowered. In addition to such an effect, in the ion source 100 of the present embodiment, the creeping distance (b) is longer than that of the ion source 100z of the comparative example, so that the effect of preventing creeping discharge can be further improved compared to the ion source of the comparative example 100z.

[0046] In particular, rare gases such as helium and argon may be used as the discharge gas filling the dielectric 121. Rare gases have the characteristic of high ionization energy. Due to this characteristic, sample molecules are ionized with high efficiency, thereby improving sensitivity. On the other hand, when a rare gas is used as the discharge gas, a high radio-frequency voltage must be applied to the outer cylindrical electrode 122 to generate plasma P. Therefore, in the ion source 100z shown in FIG. 3, when a rare gas is used as the discharge gas, creeping discharge C (see FIG. 4) is likely to occur. As described above, the ion source 100 of this embodiment can reduce the radio-frequency voltage applied to the outer cylindrical electrode 122. Furthermore, since the creeping distance is longer, even when a rare gas is used as the discharge gas, the occurrence of creeping discharge C can be suppressed compared to the ion source 100z shown in FIG. 3.

[0047] FIG. 5 is a diagram showing details of the conical inner cylindrical electrode 110a in this embodiment. The inner cylindrical electrode 110a has a main body 114 and a flange 111 provided along the outer periphery of an orifice-side opening 113 of the main body 114. The flange 111 has an outer diameter greater than at least the inner diameter of the dielectric 121 around the orifice-side opening 113.

[0048] (Manufacturing method) Next, with reference to Figures 6 to 8, a procedure for manufacturing the ion source 100 using the inner cylindrical electrode 110a shown in Figure 5 will be described. Note that the ion source 100 shown in Figures 6 to 8 differs from the ion source 100 shown in Figures 1 and 2 in the shapes of the heating unit 141 and the orifice electrode 130, etc. Figures 6 to 8 show enlarged views of the vicinity of the inner cylindrical electrode 110a of the ion source 100. Also, the configuration of the ion source 100 in Figures 6 to 8 is the same as that in Figures 1 and 2.

[0049] 6, the dielectric 121 provided with the outer cylindrical electrode 122 and the heating unit 141 are assembled. An O-ring 161 for vacuum sealing is provided at the orifice electrode side end of the heating unit 141 and on the outer periphery of the dielectric 121. Although not shown in FIG. 6, the outer cylindrical electrode 122 (see FIG. 1) is provided in the dielectric 121, and the capillary 151 (see FIG. 1) is also provided in the dielectric 121 and the heating unit 141.

[0050] Then, as shown in FIG. 6, the main body 114 of the inner cylindrical electrode 110a is inserted into the dielectric 121 so that the capillary-side opening 112 faces away from the orifice electrode 130 (white arrow in FIG. 6). After an O-ring 161 is provided between the dielectric 121 and the orifice electrode 130, the inner cylindrical electrode 110a is inserted into the dielectric 121 so that the capillary-side opening 112 faces away from the orifice electrode 130. The inserted inner cylindrical electrode 110a is locked by the flange 111 and the orifice electrode-side end of the dielectric 121 (FIG. 7). Then, the orifice electrode 130 is attached to the dielectric 121 and the heating unit 141 into which the main body 114 of the inner cylindrical electrode 110a has been inserted (white arrow in FIG. 7). In this manner, the ion source 100 shown in FIG. 8 is manufactured.

[0051] 8, after the collar portion 111 is engaged with the orifice electrode side end of the dielectric 121, the collar portion 111 is pressed against the dielectric 121 by the orifice electrode 130. That is, the collar portion 111 is sandwiched between the dielectric 121 and the orifice electrode 130. In other words, the orifice electrode 130 is provided so that the collar portion 111 of the inner cylindrical electrode 110a is sandwiched between the dielectric 121 and the orifice electrode 130. The width of the collar portion 111 may be any length as long as it can be engaged with the dielectric 121.

[0052] 8, the O-ring 161 is in contact with the dielectric 121, the orifice electrode 130, and the heating unit 141. That is, the O-ring 161 is provided at least between the dielectric 121 and the orifice electrode 130. The orifice electrode 130 is pressed against the dielectric 121 via the flange 111, thereby deforming the O-ring 161. The deformed portion of the O-ring 161 is sealed, thereby shielding the inside of the ion source 100 from the external atmospheric pressure and maintaining the inside of the dielectric 121 at a desired pressure.

[0053] As shown in FIG. 5, the provision of the flange 111 at the end of the inner cylindrical electrode 110a facilitates assembly of the ion source 100 and ensures stable installation of the inner cylindrical electrode 110a. Additionally, electrical continuity between the inner cylindrical electrode 110a and the orifice electrode 130 can be ensured. In a configuration in which a DC voltage is applied to the outer cylindrical electrode 122 and a high-frequency voltage is applied to the inner cylindrical electrode 110a, an insulating member (not shown) may be interposed between the flange 111 and the orifice electrode 130. Even in this configuration, the flange 111 of the inner cylindrical electrode 110 is (indirectly) sandwiched between the dielectric 121 and the orifice electrode 130. Even in a configuration in which an insulating member (not shown) is interposed between the flange 111 and the orifice electrode 130, the ion source 100 can be easily assembled and the inner cylindrical electrode 110a can be stably installed.

[0054] [First Modification] Figures 9 and 10 are cross-sectional views of inner cylindrical electrodes 110b and 110c in the first modified example. In Figures 9 and 10, the same components as those shown in Figure 5 are denoted by the same reference numerals, and the description thereof will be omitted. The inner cylindrical electrode 110 is not limited to the conical shape shown in Fig. 5. For example, the inner cylindrical electrodes 110b and 110c shown in Fig. 9 and Fig. 10 have a multi-step convex shape in which a plurality of cylinders with different inner and outer diameters are combined. The plurality of cylinders are combined so that the inner and outer diameters become larger toward the orifice electrode side and become smaller toward the capillary side.

[0055] 9 and 10, the inner and outer diameters of the inner cylindrical electrodes 110b and 110c taper in a stepped manner toward their tips (having a multi-step convex shape that deforms in a stepped manner). When the inner diameter of the dielectric 121 is 2 mm to 3 mm, the inner diameter of the capillary-side opening 112 at the tip of the inner cylindrical electrodes 110b and 110c is preferably approximately 0.3 mm to 1 mm, similar to the inner cylindrical electrode 110 shown in FIGS. 1 to 5. In the inner cylindrical electrodes 110b and 110c shown in FIGS. 9 and 10, the outer and inner diameters of the capillary-side opening 112 are also smaller than the orifice-side opening 113. Therefore, when a high-frequency voltage is applied to the inner cylindrical electrodes 110b and 110c and the outer cylindrical electrode 122, an electric field is concentrated at the tips of the inner cylindrical electrodes 110b and 110c. As a result, plasma P can be generated at a lower voltage than the ion source 100z shown in FIG. 3. Therefore, the inner cylindrical electrodes 110b, 110c shown in FIGS. 9 and 10 can also prevent creeping discharge C (see FIG. 4). Furthermore, similar to FIGS. 1 and 2, the tips of the inner cylindrical electrodes 110b, 110c are tapered. This prevents the electric field generated by the high-frequency voltage applied to the outer cylindrical electrode 122 from penetrating inside the inner cylindrical electrodes 110b, 110c, similar to FIGS. 1 to 5. As a result, similar to the inner cylindrical electrode 110 shown in FIGS. 1 and 2, primary ions present inside the inner cylindrical electrodes 110b, 110c can remain without being affected by the electric field. This allows primary ions to collide with sample molecules for a sufficient period of time, improving the ionization efficiency of the sample molecules. These effects of the inner cylindrical electrodes 110b, 110c shown in FIGS. 9 and 10 enable the realization of an ion source 100 and mass spectrometer 1 with high durability (improved robustness) and high sensitivity.

[0056] 9 shows an example of a two-stage convex inner cylindrical electrode 110b, and FIG. 10 shows an example of a three-stage convex inner cylindrical electrode 110c, but the number of stages (number of cylinders) of the convex shape may be further increased. As the number of stages increases, the characteristics of the ion source 100 become closer to the conical shape shown in FIG. 5.

[0057] [Second Modification] Figures 11 and 12 are cross-sectional views of inner cylindrical electrodes 110d and 110e in the second modified example. In Figures 11 and 12, the same components as those shown in Figure 5 are denoted by the same reference numerals, and the description thereof will be omitted. The shape of the inner cylindrical electrode 110 is not limited to the conical shape shown in Figures 1 to 5 or the stepped convex shape (multi-step convex shape) shown in Figures 9 and 10. For example, the shape of the inner cylindrical electrodes 110d, 110e shown in Figures 11 and 12 may be a shape that combines a conical shape and a cylindrical shape (a combination of a conical shape and a convex shape). In the inner cylindrical electrodes 110d, 110e shown in FIGS. 11 and 12, the outer and inner diameters of the capillary-side opening 112 are smaller than the orifice-side opening 113. Therefore, when a high-frequency voltage is applied to the inner cylindrical electrodes 110d, 110e and the outer cylindrical electrode 122 (see FIG. 1), an electric field is concentrated at the tip of the inner cylindrical electrodes 110d, 110e. As a result, plasma P can be generated at a lower voltage than in the ion source 100z shown in FIG. 3. Furthermore, because the tip of the inner cylindrical electrodes 110d, 110e is tapered, the electric field generated by the high-frequency voltage of the outer cylindrical electrode 122 is prevented from penetrating into the inner cylindrical electrodes 110d, 110e. As a result, sample molecules are ionized with high efficiency inside the inner cylindrical electrodes 110d, 110e, as in FIGS. 1 to 10. Due to the above effects, even if the shape of the inner cylindrical electrodes 110d, 110e is a combination of a conical shape and a convex shape as shown in FIGS. 11 and 12, it is possible to realize a highly durable and highly sensitive ion source 100 and mass spectrometer 1.

[0058] An object of the present embodiment is to provide a highly durable ion source 100 and mass spectrometer 1 that can stably ionize sample molecules even over long periods of use by making creeping discharge less likely to occur. Furthermore, by allowing primary ions to collide with sample molecules for a sufficient period of time, the ionization of sample molecules can be promoted, making it possible to provide a highly sensitive ion source 100 and mass spectrometer 1.

[0059] To address this issue, in this embodiment, the inner and outer diameters of the inner cylindrical electrodes 110 (110a to 110e) are gradually reduced toward the outer cylindrical electrode 122, as shown in FIGS.

[0060] With this configuration, an electric field is concentrated at the tip of the inner cylindrical electrode 110. This allows plasma P to be easily generated even when the high-frequency voltage applied by the high-frequency power supply AC is lower than that of the ion source 100z shown in FIGS. 3 and 4. Furthermore, since the tip of the inner cylindrical electrode 110 is spaced apart from the dielectric 121, the creeping distance is increased. These effects reduce the likelihood of creeping discharge C (see FIG. 4). In other words, a highly durable (improved robustness) ion source 100 and mass spectrometer 1 can be realized that are resistant to contamination and capable of stably ionizing sample molecules even after long-term use. Furthermore, by narrowing the tip of the inner cylindrical electrode 110, the electric field generated by the high-frequency applied to the outer cylindrical electrode 122 is prevented from penetrating inside the inner cylindrical electrode 110. This effectively creates a nearly electric-field-free state inside the inner cylindrical electrode 110, lengthening the residence time of primary ions. As a result, sample molecules and primary ions can collide for a sufficient period of time. Therefore, the ionization efficiency of the sample molecules is improved, and as a result, a highly sensitive ion source 100 and mass spectrometer 1 can be realized.

[0061] The present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations.

[0062] In addition, in each embodiment, the control lines and information lines shown are those that are considered necessary for explanation, and not all control lines and information lines in the product are necessarily shown. In reality, it can be considered that almost all components are interconnected. [Explanation of symbols]

[0063] 1,1z mass spectrometer 100,100z ion source 110,110a~110e,110z Inner cylinder electrode 111 Brim 112 Capillary side opening (first opening) 113 Orifice side opening (second opening) 114 Main body 121 Dielectric 122 Outer cylindrical electrode 130 Orifice electrode 131 Orifice 141 Heating section 151 Capillary 161 O-ring 200 Mass spectrometry department AC high frequency power supply DC1 First DC power supply F ionization region P plasma

Claims

1. a cylindrical dielectric into which a discharge gas and a sample are introduced; an outer cylindrical electrode that is installed so as to be in close contact with the outside of the dielectric body and to which one of an AC voltage having a predetermined frequency and a DC voltage is applied; an inner cylindrical electrode that is installed inside the dielectric so as to be in close contact with the dielectric and to which the other of the AC voltage and the DC voltage is applied; an orifice electrode having an orifice for drawing ions generated by discharge between the outer cylindrical electrode and the inner cylindrical electrode to the outside of the dielectric; and The inner cylindrical electrode is Both ends are open, and one end is connected to the orifice electrode, a first opening that is an opening on the opposite side to the orifice electrode side; a second opening that is separate from the first opening, The outer diameter of the first opening is less than the outer diameter of the second opening. An ion source characterized by:

2. Regarding the inner cylindrical electrode, The inner diameter of the first opening is less than the inner diameter of the second opening.

2. The ion source of claim 1.

3. The inner cylindrical electrode has a conical shape that changes continuously.