A vacuum ultraviolet photoionization-photochemical ionization combined ionization source

Abstract

A vacuum ultraviolet photoionization-photochemical ionization combined ionization source comprises an ionization source cavity and a vacuum ultraviolet light source, the ionization source cavity is a hollow closed cavity, a lamp head repulsion electrode, a radio frequency coupling electrode, a photoelectron emission grid electrode, an ionization zone transmission electrode, an ionization zone ion guide electrode and an ionization zone exit grid electrode are arranged in the ionization source cavity; a circular light shielding electrode is arranged at a middle position of the ion guide zone, the light shielding electrode is a flat plate electrode, and the outer diameter of the light shielding electrode is smaller than the inner diameter of the ion through hole of the ionization zone ion guide electrode. The application realizes efficient vacuum ultraviolet photoionization and photochemical ionization based on a single VUV light source, can effectively widen the range of samples that can be detected by a photoionization mass spectrometer, improves the detection sensitivity of the instrument, and has wide application prospects in the fields of atmospheric environment detection, industrial process monitoring and high-throughput analysis of metabolites.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mass spectrometry instruments, in particular to an ionization source of a mass spectrometer, and specifically to a vacuum ultraviolet photoionization-photochemical ionization combined ionization source. BACKGROUND

[0002] Mass spectrometry is an analytical instrument that identifies the chemical composition of a substance by measuring the mass-to-charge ratio (mass-to-charge ratio) of ions. It has the advantages of good universality, high resolution and sensitivity, and fast analysis speed. Mass spectrometry first requires ionization of molecules or atoms of a substance in an ionization source, and then enters a mass analyzer for separation and analysis. The ionization source not only determines the characteristics of the mass spectrum obtained, but also greatly affects the sensitivity and accuracy of the entire instrument. Thanks to the emergence of various "soft" ionization sources, online mass spectrometry technology has developed rapidly in recent years and is increasingly widely used in public safety, environmental detection, process monitoring, and in vitro diagnosis.

[0003] Vacuum ultraviolet photoionization (VUV-PI) is a threshold photoionization technology that directly ionizes a substance molecule by absorbing VUV photons with energy greater than its ionization energy (IE). It has high molecular ion yield and low fragmentation, making it a highly efficient "soft" ionization technique for mass spectrometry. In photoionization mass spectrometry, inert gas discharge lamps are commonly used as VUV light sources, such as krypton (Kr) discharge lamps. Compared to large-scale synchrotron radiation sources and lasers, VUV lamps have the advantages of small size, low cost, low power consumption, easy operation, and maintenance. However, due to the limitations of light window materials, the highest energy VUV photons that can be transmitted through lithium fluoride materials are no more than 11.8 eV, while the highest photon energy emitted by the commonly used Kr lamp is only 10.6 eV. For some high ionization energy compounds, such as acetonitrile (IE = 12.20 eV) and formaldehyde (IE = 10.88 eV), effective ionization is not possible, limiting the application range of photoionization mass spectrometry. Chemical ionization (CI) is a "soft" ionization technique that ionizes a compound molecule through ion-molecule reactions. It uses proton transfer (PTR), charge transfer (CE), and electrophilic addition (EA) reactions between reagent ions and sample molecules to obtain molecular ions or quasi-molecular ions of the compound being tested. For example, formaldehyde can be effectively ionized through PTR reactions with hydronium ions (H3O + ) to produce protonated ions of formaldehyde. By combining vacuum ultraviolet photoionization and chemical ionization, different ionization modes can be used for different properties of compound molecules, effectively improving ionization efficiency and expanding the application range of online mass spectrometry instruments.

[0004] A Chinese invention patent [201010567193.0] discloses a vacuum ultraviolet photoionization and chemical ionization combined ion source for mass spectrometry. The photoelectrons generated by VUV light irradiation on the surface of a metal electrode are accelerated by an electrostatic field, and a large number of reagent ions are generated by bombarding reagent gas molecules, and then chemical ionization occurs between the sample molecules. However, on the one hand, the design uses a direct current field to regulate the energy of photoelectrons, which makes high-energy electrons finally hit the light window surface of the vacuum ultraviolet light source, causing damage to the light window and easily adsorbing contaminants. On the other hand, the vacuum ultraviolet light beam penetrates through the entire ionization area, exits from the differential interface plate small hole of the ionization area, reaches the ion transmission system at the rear end, and generates photoelectrons through the photoelectric effect, and then generates ion interference under the action of the electric field of the ion transmission system. A Chinese invention patent [201810099383.0] discloses a volatile organic compound detection device and method for chemical ionization and photoionization combined source mass spectrometry. Through chemical ionization and photoionization, multi-dimensional ionization and high-sensitivity mass spectrometry detection of volatile organic compounds are achieved, which makes up for the deficiencies of chemical ionization such as proton transfer reaction and difficulty in detecting alkane volatile organic compounds, and low photoionization efficiency under vacuum conditions. However, on the one hand, the chemical ionization of the invention uses a discharge ion source to generate reagent ions, and the photoionization is realized by a separately arranged photoionization lamp, which increases the complexity of the structure and has high power consumption. On the other hand, the VUV light generated by the photoionization lamp also irradiates from the outlet small hole of the ionization area to the ion transmission system behind, causing ion interference. SUMMARY

[0005] The purpose of the present application is to provide a vacuum ultraviolet photoionization-photo-induced chemical ionization combined ion source based on a single VUV light source. On the one hand, a reagent ion generation area is arranged near the VUV light window, and the energy of photoelectrons is controlled by a radio frequency electric field to generate reagent ions, reducing the impact on the VUV light window and ion transmission. On the other hand, a light-shielding electrode is used to shield the VUV light beam, effectively preventing the VUV light from irradiating from the outlet small hole of the ionization area to the ion transmission system behind, causing ion interference.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A vacuum ultraviolet photoionization-photo-induced chemical ionization combined ion source includes an ion source cavity and a vacuum ultraviolet light source. The ion source cavity is a hollow sealed chamber, and inside the ion source cavity, there are a lamp head repulsion electrode, a radio frequency coupling electrode, a photoelectron emission grid electrode, an ionization area transmission electrode, an ionization area ion guide electrode, and an ionization area exit grid electrode.

[0008] The lamp head repulsion electrode, the radio frequency coupling electrode, the photoelectron emission grid electrode, the ionization zone transmission electrode, the ionization zone ion guide electrode and the ionization zone exit grid electrode are all flat plate electrodes with a circular ion through hole in the middle part, and the flat plate electrodes are arranged in parallel with the through holes coaxial and spaced from each other; wherein the ionization zone transmission electrode and the ionization zone ion guide electrode are each one or more than two flat plate electrodes arranged in parallel with the through holes coaxial and spaced from each other, and the ion through hole inner diameter of the ionization zone ion guide electrode is greater than or equal to the ion through hole inner diameter of the ionization zone transmission electrode; the ion through hole regions of the photoelectron emission grid electrode and the ionization zone exit grid electrode are provided with a metal grid for shielding electric field;

[0009] The ion through hole in the middle part of the radio frequency coupling electrode and the region between the ion through holes of the adjacent two flat plate electrodes serve as a photoelectron ionization zone; the ion through hole in the middle part of the ionization zone transmission electrode composed of one or more than two flat plate electrodes and the region between the ion through holes of the adjacent two flat plate electrodes serve as a reaction ionization zone; the ion through hole in the middle part of the ionization zone ion guide electrode composed of one or more than two flat plate electrodes and the region between the ion through holes of the adjacent two flat plate electrodes serve as an ion guide zone; a circular light shielding electrode is arranged at the middle part of the ion guide zone, and the light shielding electrode is a flat plate electrode with an outer diameter less than the ion through hole inner diameter of the ionization zone ion guide electrode;

[0010] The vacuum ultraviolet light emitted by the vacuum ultraviolet light source is located inside the ionization source cavity, converges through a focusing lens, and then sequentially passes through the ion through hole center regions of the lamp head repulsion electrode, the radio frequency coupling electrode, the photoelectron emission grid electrode, the ionization zone transmission electrode and the ionization zone ion guide electrode, and irradiates on the surface of the light shielding electrode; the ionization zone exit grid electrode is arranged on the cavity wall at the bottom of the ionization source cavity, and the middle through hole of the ionization zone exit grid electrode is connected with the outside of the ionization source cavity through the through hole arranged on the cavity wall of the ionization source cavity;

[0011] Different direct current voltages are sequentially loaded on the flat plate electrodes of the lamp head repulsion electrode, the radio frequency coupling electrode, the photoelectron emission grid electrode, the ionization zone transmission electrode, the ionization zone ion guide electrode and the ionization zone exit grid electrode in the order of voltage from high to low, and an ion transmission electric field with a size of 0.1-1000 V / cm is formed in the axial direction of the lamp head repulsion electrode to the ionization zone exit grid electrode; a direct current voltage higher than that of the ionization zone ion guide electrode is applied to the light shielding electrode;

[0012] A peak-to-peak value V p-p of 0-1000 V radio frequency voltage is coupled to the direct current voltage of the radio frequency coupling electrode, and a radio frequency electric field is formed in the ion through hole region between the lamp head repulsion electrode, the radio frequency coupling electrode and the photoelectron emission grid electrode;

[0013] The photoelectron ionization zone gas sampling tube extends into the ionization source cavity through the outer wall of the ionization source cavity, and the gas outlet of the reagent gas sampling tube is arranged in the region spaced apart from each other between the push-pull electrode and the radio frequency coupling electrode.

[0014] The photoelectron ionization zone gas sampling tube extends into the ionization source cavity through the outer wall of the ionization source cavity, and the gas outlet of the reagent gas sampling tube is arranged in the region spaced apart from each other between the push-pull electrode and the radio frequency coupling electrode.

[0015] A gas outlet is arranged on the side wall of the ionization source cavity, the gas outlet is connected to the inlet end of the vacuum valve through the vacuum pipeline, the outlet end of the vacuum valve is connected to the vacuum pump through the vacuum pipeline, and the vacuum degree inside the ionization source cavity is maintained at 10 -3 ~10 2 mbar.

[0016] An insulating material is arranged between the ionization source cavity and the exit grid electrode of the ionization zone to achieve vacuum sealing and mutual insulation therebetween.

[0017] A metal grid for shielding electric field is arranged on the ionization grid electrode and the ionization exit grid electrode of the ionization zone, and the metal grid is arranged along the radial direction of the ion tunnel, i.e. perpendicular to the surface of the electrode.

[0018] A radio frequency focusing lens and a mass analyzer are sequentially arranged at the rear end of the metal grid of the ionization exit grid electrode away from the vacuum ultraviolet light source, i.e. the ions emitted from the ionization source cavity are directly introduced into the mass analyzer after being modulated by the radio frequency focusing lens;

[0019] The radio frequency focusing lens is an ion funnel composed of two or more than three metal ring-shaped flat electrodes which are coaxial, parallel, and gradually reduced in diameter from the center of the ionization exit grid electrode, or a quadrupole rod, a hexapole rod or an octupole rod electrode composed of four, six or eight parallel metal rods.

[0020] The mass analyzer is a quadrupole rod mass analyzer, an ion trap mass analyzer, a magnetic mass analyzer or a time-of-flight mass analyzer.

[0021] The vacuum ultraviolet light source is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source.

[0022] The vacuum ultraviolet photoionization-photochemical ionization combined ion source provided by the application adjusts and controls photoelectrons generated by photoelectric effect to reciprocating oscillation movement by arranging a radio frequency electric field in the area close to the VUV light window, and efficiently ionizes reagent gas molecules to obtain reagent ions for chemical ionization. Compared with the single direction acceleration of electrons by a direct current electric field, the introduction of the radio frequency electric field can effectively avoid high-speed photoelectrons from hitting the VUV light window or the surface of a metal electrode, and reduce the pollution caused thereby. An optical shielding electrode is arranged in the middle of the ion guide area close to the outlet of the ion source, so that VUV light cannot directly enter the ion transmission system at the rear end of the ionization area, thus avoiding the generation of photoelectrons in the ion transmission system by photoelectric effect, and the ion interference caused by the acceleration of photoelectrons by the electric field of the ion transmission system. A direct current voltage higher than that of the ion guide electrode of the ionization area is applied to the optical shielding electrode to form an ion guide electric field, so that the ions generated in the ionization area bypass the optical shielding electrode under the action of the electric field in the ion guide area, and converge to the outlet of the exit grid electrode of the ionization area, thereby realizing efficient transmission. The application realizes efficient vacuum ultraviolet photoionization and photochemical ionization based on a single VUV light source, can effectively widen the range of samples that can be detected by a photoionization mass spectrometer, improve the detection sensitivity of the instrument, and has wide application prospects in the fields of atmospheric environment detection, industrial process monitoring, and high-throughput analysis of metabolites. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a structure schematic diagram of a vacuum ultraviolet photoionization-photochemical ionization combined ion source of the application.

[0024] Figure 2 It is a structure schematic diagram of a vacuum ultraviolet photoionization-photochemical ionization combined ion source working in a vacuum ultraviolet photoionization mode of the application.

[0025] Figure 3 It is a structure schematic diagram of a vacuum ultraviolet photoionization-photochemical ionization combined ion source working in a photochemical ionization mode of the application.

[0026] Figure 4 It is an electric field and ion flight trajectory simulation schematic diagram of a reaction ionization area and an ion guide area of the application. DETAILED DESCRIPTION

[0027] Please refer to Figure 1 , it is a structure schematic diagram of the application. The vacuum ultraviolet photoionization-photochemical ionization combined ion source of the application includes an ion source cavity 1 and a vacuum ultraviolet light source 2. The ion source cavity 1 is a hollow closed chamber, and the lamp head repulsion electrode 4, the radio frequency coupling electrode 5, the photoelectron emission grid electrode 6, the ionization area transmission electrode 7, the ionization area ion guide electrode 8 and the ionization area exit grid electrode 9 are arranged in the ion source cavity 1.

[0028] The lamp head repulsion electrode 4, the radio frequency coupling electrode 5, the photoelectron emission grid electrode 6, the ionization zone transmission electrode 7, the ionization zone ion guide electrode 8 and the ionization zone exit grid electrode 9 are all plate-shaped electrodes with a circular ion through hole in the middle, and the plate-shaped electrodes are sequentially and coaxially arranged in parallel; wherein the ionization zone transmission electrode 7 and the ionization zone ion guide electrode 8 are both one or more than two plate-shaped electrodes arranged in parallel and coaxially, and the inner diameter of the ion through hole of the ionization zone ion guide electrode 8 is greater than or equal to the inner diameter of the ion through hole of the ionization zone transmission electrode 7; the ion through hole regions of the photoelectron emission grid electrode 6 and the ionization zone exit grid electrode 9 are both provided with a metal grid for shielding an electric field;

[0029] The ion through hole in the middle of the radio frequency coupling electrode 5 and the region between the ion through holes of the adjacent two plate-shaped electrodes serve as a photoelectron ionization zone; the ion through hole in the middle of the ionization zone transmission electrode 7 composed of one or more than two plate-shaped electrodes and the region between the ion through holes of the adjacent two plate-shaped electrodes serve as a reaction ionization zone; the ion through hole in the middle of the ionization zone ion guide electrode 8 composed of one or more than two plate-shaped electrodes and the region between the ion through holes of the adjacent two plate-shaped electrodes serve as an ion guide zone; a circular light shielding electrode 10 is arranged at the middle position of the ion guide zone, and the light shielding electrode 10 is a plate-shaped electrode with an outer diameter smaller than the inner diameter of the ion through hole of the ionization zone ion guide electrode 8;

[0030] The vacuum ultraviolet light 17 emitted by the vacuum ultraviolet light source 2 is located inside the ionization source cavity 1, is converged by the focusing lens 3, sequentially passes through the ion through hole center regions of the lamp head repulsion electrode 4, the radio frequency coupling electrode 5, the photoelectron emission grid electrode 6, the ionization zone transmission electrode 7 and the ionization zone ion guide electrode 8, and irradiates on the surface of the light shielding electrode 10; the ionization zone exit grid electrode 9 is arranged on the cavity wall at the bottom of the ionization source cavity 1, and the middle through hole of the ionization zone exit grid electrode 9 is connected with the outside of the ionization source cavity 1 through the through hole arranged on the cavity wall of the ionization source cavity 1;

[0031] Different direct voltages are sequentially loaded on the plate-shaped electrodes of the lamp head repulsion electrode 4, the radio frequency coupling electrode 5, the photoelectron emission grid electrode 6, the ionization zone transmission electrode 7, the ionization zone ion guide electrode 8 and the ionization zone exit grid electrode 9 in the order of voltage from high to low, and an ion transmission electric field with a size of 0.1-1000 V / cm is formed in the axial direction of the lamp head repulsion electrode 4 to the ionization zone exit grid electrode 9;

[0032] A photoelectron ionization zone gas sampling tube 12 penetrates into the ionization source cavity 1 through the outer wall of the ionization source cavity 1, and the gas outlet of the reagent gas sampling tube 12 is arranged in the region between the lamp head repulsion electrode 4 and the radio frequency coupling electrode 5;

[0033] A reaction ionization region gas inlet tube 13 extends into the ionization source cavity 1 through the outer wall of the ionization source cavity 1, and the gas outlet of the sample gas inlet tube 13 is arranged in the region between the photoelectron emission grid electrode 6 and the ionization region transmission electrode 7.

[0034] A gas outlet is arranged on the side wall of the ionization source cavity 1, the gas outlet is connected to the inlet end of the vacuum valve 14 through a vacuum pipeline, the outlet end of the vacuum valve 14 is connected to the vacuum pump 15 through a vacuum pipeline, and the vacuum degree inside the ionization source cavity 1 is maintained at 10 -3 ~10 2 mbar.

[0035] An insulating material is arranged between the ionization region exit grid electrode 9 and the ionization source cavity 1 to achieve vacuum sealing and mutual insulation therebetween.

[0036] Metal grids for shielding electric field are arranged on the ion transmission hole regions of the photoelectron emission grid electrode 6 and the ionization region exit grid electrode 9, and the metal grids are arranged along the radial direction of the ion transmission holes, i.e. perpendicular to the surface of the electrode.

[0037] A radio frequency focusing lens 11 and a mass analyzer 16 are sequentially arranged at the rear end of the metal grid of the ionization region exit grid electrode 9 away from the vacuum ultraviolet light source 2, i.e. the ions emitted from the ionization source cavity 1 are directly introduced into the mass analyzer 16 after being modulated by the radio frequency focusing lens 11;

[0038] The radio frequency focusing lens 11 is an ion funnel composed of two or more than three metal ring-shaped flat electrodes which are coaxial, parallel, have central through holes, and gradually decrease in diameter in the radial direction away from the ionization region exit grid electrode 9, or a quadrupole rod, hexapole rod or octupole rod electrode composed of four, six or eight parallel metal rods.

[0039] The mass analyzer 16 is a quadrupole rod mass analyzer, an ion trap mass analyzer, a magnetic mass analyzer or a time-of-flight mass analyzer.

[0040] The vacuum ultraviolet light source 2 is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source.

[0041] In application, by changing the type of gas introduced into the ionization source and the applied voltage condition, the composite ionization source can work in vacuum ultraviolet photoionization and photochemical ionization modes respectively. When the composite ionization source works in the vacuum ultraviolet photoionization mode, sample gas is simultaneously introduced into the photoelectron ionization region gas inlet tube 12 and the reaction ionization region gas inlet tube 13, and only a relatively low direct current voltage (coupling peak-peak value V p-pThe photoelectrons generated by the VUV light irradiating on the metal grid of the photoelectron emission grid electrode 6 are not enough to obtain sufficient energy to produce photoelectron ionization, at this time the sample molecules mainly absorb VUV photons to produce photoionization. When the compound ionization source works in the vacuum ultraviolet photoionization mode, the reagent gas and the sample gas are respectively introduced into the gas inlet pipe 12 of the photoelectron ionization area and the gas inlet pipe 13 of the reaction ionization area, and the peak-to-peak value V p-p RF voltage of 0V, the ion transmission hole area between the lamp head repulsion electrode 4, the RF coupling electrode 5 and the photoelectron emission grid electrode 6 forms an RF electric field, and the photoelectrons generated by the VUV light irradiating on the metal grid of the photoelectron emission grid electrode 6 can obtain sufficient energy to make the reagent gas molecules produce photoelectron ionization under the action of the RF electric field, so that a large amount of reagent ions are obtained, and the reagent ions further enter the reaction ionization area to produce ion-molecule reactions with the sample molecules, so that the sample molecules are efficiently ionized. A direct current voltage higher than that of the ion guide electrode 8 of the ionization area is applied to the light shielding electrode 10 to form an ion guide electric field, and the ions generated in the ionization area bypass the light shielding electrode 10 under the action of the electric field in the ion guide area and converge to the outlet of the ionization area exit grid electrode 9, so that efficient transmission is realized.

[0042] Example 1

[0043] As shown in Figure 2 The vacuum ultraviolet photoionization-photochemical ionization compound ionization source of the present application works in the vacuum ultraviolet photoionization mode. The vacuum ultraviolet light source 2 adopts a gas discharge lamp light source, the sample gas is simultaneously introduced into the gas inlet pipe 12 of the photoelectron ionization area and the gas inlet pipe 13 of the reaction ionization area, different direct current voltages are sequentially loaded on the flat plate electrodes of the lamp head repulsion electrode 4, the RF coupling electrode 5, the photoelectron emission grid electrode 6, the ionization area transmission electrode 7, the ionization area ion guide electrode 8 and the ionization area exit grid electrode 9 in the order of high to low voltage, and an ion transmission electric field with a size of 20V / cm is formed in the axial direction of the lamp head repulsion electrode 4 to the ionization area exit grid electrode 9; the peak-to-peak value V p-p RF voltage of 0V, at this time the sample molecules mainly absorb VUV photons to produce photoionization. The sample ions pass through the metal grid in the middle of the photoelectron emission grid electrode 6 to enter the rear-end reaction ionization area and the ion guide area, bypass the light shielding electrode 10 under the action of the electric field in the ion guide area, converge to the outlet of the ionization area exit grid electrode 9, and then enter the RF focusing lens 11 composed of four rods, and finally reach the time-of-flight mass analyzer 16 for mass analysis.

[0044] Example 2

[0045] As shown in Figure 3The vacuum ultraviolet photoionization-photochemical ionization combined ionization source of the present application works in the photochemical ionization mode. The vacuum ultraviolet light source 2 adopts a gas discharge lamp light source, reagent gas and sample gas are respectively introduced into the photoelectron ionization zone gas inlet tube 12 and the reaction ionization zone gas inlet tube 13, different direct current voltages are loaded on the flat plate electrodes of the lamp head repulsion electrode 4, the radio frequency coupling electrode 5, the photoelectron emission grid electrode 6, the ionization zone transmission electrode 7, the ionization zone ion guide electrode 8 and the ionization zone exit grid electrode 9 in the order of high to low voltage, and an ion transmission electric field with a size of 100 V / cm is formed in the axial direction of the lamp head repulsion electrode 4 to the ionization zone exit grid electrode 9. The peak-to-peak value V p-p is 200 V, at this time, the photoelectrons generated by the VUV light irradiating on the metal grid of the photoelectron emission grid electrode 6 can obtain sufficient energy to make the reagent gas molecules produce photoelectron ionization under the action of the radio frequency electric field, a large amount of reagent ions are obtained, the reagent ions enter the reaction ionization zone again and ion-molecule reactions occur between the sample molecules, so that the sample molecules are efficiently ionized. The sample ions are affected by the electric field in the ion guide zone, bypass the light shielding electrode 10, and converge to the outlet of the ionization zone exit grid electrode 9, then enter the radio frequency focusing lens 11 composed of ion funnels, and finally reach the quadrupole rod mass analyzer 16 for mass analysis.

[0046] Figure 4 The electric field and ion flight trajectory simulation schematic diagram of the reaction ionization zone and the ion guide zone of the present application. A direct current voltage higher than that of the ionization zone ion guide electrode 8 is applied to the light shielding electrode 10 to form an ion guide electric field, which can make the sample ions converge to the outlet of the ionization zone exit grid electrode 9 after bypassing the light shielding electrode 10, and at the same time achieve the purposes of VUV light beam shielding and ion efficient transmission.

Claims

1. A vacuum ultraviolet photoionization-photochemical ionization combined ionization source, comprising an ionization source cavity (1) and a vacuum ultraviolet light source (2), the ionization source cavity (1) is a hollow closed chamber, and a lamp head repulsion electrode (4), a radio frequency coupling electrode (5), a photoelectron emission grid electrode (6), an ionization zone transmission electrode (7), an ionization zone ion guide electrode (8) and an ionization zone exit grid electrode (9) are arranged inside the ionization source cavity (1), characterized in that: The lamp head repulsion electrode (4), the radio frequency coupling electrode (5), the photoelectron emission grid electrode (6), the ionization zone transmission electrode (7), the ionization zone ion guide electrode (8) and the ionization zone exit grid electrode (9) are all plate-shaped electrodes with a circular ion through hole arranged in the middle, and the plate-shaped electrodes are sequentially arranged in parallel with the through holes coaxial and spaced apart; wherein the ionization zone transmission electrode (7) and the ionization zone ion guide electrode (8) are each one or more than two plate-shaped electrodes arranged in parallel with the through holes coaxial and spaced apart, and the inner diameter of the ion through hole of the ionization zone ion guide electrode (8) is greater than or equal to the inner diameter of the ion through hole of the ionization zone transmission electrode (7); metal grids for shielding electric field are arranged in the ion through hole regions of the photoelectron emission grid electrode (6) and the ionization zone exit grid electrode (9); The ion through hole in the middle of the radio frequency coupling electrode (5) and the region between the ion through holes of the adjacent two plate-shaped electrodes serve as a photoelectron ionization zone; the ion through hole in the middle of the ionization zone transmission electrode (7) composed of one or more than two plate-shaped electrodes and the region between the ion through holes of the adjacent two plate-shaped electrodes serve as a reaction ionization zone; the ion through hole in the middle of the ionization zone ion guide electrode (8) composed of one or more than two plate-shaped electrodes and the region between the ion through holes of the adjacent two plate-shaped electrodes serve as an ion guide zone; a circular light shielding electrode (10) is arranged at the middle position of the ion guide zone, the light shielding electrode (10) is a plate-shaped electrode with an outer diameter smaller than the inner diameter of the ion through hole of the ionization zone ion guide electrode (8); The vacuum ultraviolet light (17) emitted by the vacuum ultraviolet light source (2) is located inside the ionization source cavity (1), converges through a focusing lens (3) and then sequentially passes through the ion through hole center regions of the lamp head repulsion electrode (4), the radio frequency coupling electrode (5), the photoelectron emission grid electrode (6), the ionization zone transmission electrode (7) and the ionization zone ion guide electrode (8), and irradiates on the surface of the light shielding electrode (10); the ionization zone exit grid electrode (9) is arranged on the cavity wall at the bottom of the ionization source cavity (1), and the middle through hole of the ionization zone exit grid electrode (9) is connected with the outside of the ionization source cavity (1) through a through hole arranged on the cavity wall of the ionization source cavity (1). A DC voltage is loaded on the flat electrodes of the lamp head repulsion electrode (4), the radio frequency coupling electrode (5), the photoelectron emission grid electrode (6), the ionization zone transmission electrode (7), the ionization zone ion guide electrode (8) and the ionization zone exit grid electrode (9) in order from high to low, forming an ion transmission electric field with a size of 0.1-1000 V / cm in the axial direction of the lamp head repulsion electrode (4) to the ionization zone exit grid electrode (9); a DC voltage higher than that of the ionization zone ion guide electrode (8) is applied to the light shielding electrode (10); The peak-to-peak value V of the DC voltage coupled to the radio frequency coupling electrode (5) is 0 ~ 1000 V p-p The radio frequency voltage is 0 ~ 1000 V, and the radio frequency electric field is formed in the ion tunnel region between the lamp head repulsion electrode (4), the radio frequency coupling electrode (5), and the photoelectron emission grid electrode (6). A photoelectron ionization zone gas sampling tube (12) penetrates through the outer wall of the ionization source cavity (1) and extends into the ionization source cavity (1), and the gas outlet of the reagent gas sampling tube (12) is arranged in the region spaced from each other between the lamp head repulsion electrode (4) and the radio frequency coupling electrode (5); A reaction ionization zone gas sampling tube (13) penetrates through the outer wall of the ionization source cavity (1) and extends into the ionization source cavity (1), and the gas outlet of the sample gas sampling tube (13) is arranged in the region spaced from each other between the photoelectron emission grid electrode (6) and the ionization zone transmission electrode (7).

2. The composite ionization source according to claim 1, characterized in that: A gas outlet is arranged on the side wall of the ion source cavity (1), the gas outlet is connected with the inlet end of the vacuum valve (14) through a vacuum pipeline, the outlet end of the vacuum valve (14) is connected with the vacuum pump (15) through a vacuum pipeline, the vacuum degree inside the ion source cavity (1) is maintained at 10 -3 ~10 2 mbar.

3. The composite ionization source according to claim 1, characterized in that: An insulating material is arranged between the ionization zone exit grid electrode (9) and the ionization source cavity (1) to realize vacuum sealing and mutual insulation therebetween.

4. The composite ionization source according to claim 1, characterized in that: Metal grids for shielding electric field are arranged in the ion transmission hole regions of the photoelectron emission grid electrode (6) and the ionization zone exit grid electrode (9), and the metal grids are arranged along the radial direction of the ion transmission hole, i.e. perpendicular to the surface of the electrode.

5. The composite ionization source according to claim 1 or 4, characterized in that: A radio frequency focusing lens (11) and a mass analyzer (16) are sequentially arranged at the rear end of the metal grid of the ionization zone exit grid electrode (9) away from the vacuum ultraviolet light source (2), i.e. the ions emitted from the ionization source cavity (1) are directly introduced into the mass analyzer (16) after being modulated by the radio frequency focusing lens (11); The radio frequency focusing lens (11) is an ion funnel composed of two or more than three metal ring-shaped flat electrodes which are coaxial, parallel and spaced from each other, and the inner diameter of the central circular hole gradually decreases in the direction away from the ionization zone exit grid electrode (9), or a quadrupole rod, hexapole rod or octapole rod electrode composed of four, six or eight parallel metal rods; The mass analyzer (16) is a quadrupole rod mass analyzer, an ion trap mass analyzer, a magnetic mass analyzer or a time-of-flight mass analyzer.

6. The composite ionization source according to claim 1, characterized in that: The vacuum ultraviolet light source (2) is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source.

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