Photoinduced Penning ionization mass spectrometry method

Abstract

The invention belongs to the field of mass spectrum ionization, and particularly relates to a photoinduced Penning ionization mass spectrum method. Photoelectrons generated by a photoelectric effect accelerate in an electric field to obtain enough energy, helium He, neon Ne and argon Ar in ground states are excited to metastable states, and the energy of the metastable states of the neutral atoms is higher than 10.6 eV (He excitation energy is 20.62 eV and 19.82 eV); the excitation energy of Ne is 16.72 eV, and the excitation energy of Ne is 16.62 eV; the excitation energy of Ar is 11.72 eV and 11.55 eV), sample molecules with ionization energy higher than photon energy and incapable of being ionized by traditional photoionization can be ionized through Penning ionization, so that the reduction of mass spectrum resolution, sensitivity and quantitative capacity caused by a space charge effect caused by coulomb repulsion among too strong reagent ions in an ion transmission process is avoided, and the detection sensitivity is improved. And damage of too strong reagent ions to the ion detector. The sensitivity can be improved by about 5 times for sample molecules ionized by traditional photo ionization energy, such as toluene, with ionization energy lower than photon energy.

Description

Technical Field

[0001] The invention belongs to the field of mass spectrometry ionization, and in particular relates to a photo-induced Penning ionization mass spectrometry method. Background Art

[0002] Photoionization is a threshold ionization technique, meaning that sample molecules are ionized when the energy of the photons absorbed exceeds their ionization energy. Currently, the most widely used krypton lamps emit photons with energies of 10.0 and 10.6 eV. Sample molecules with ionization energies above 10.6 eV cannot be effectively ionized and require other ionization methods.

[0003] Chinese invention patent (201010567193.0) discloses a composite ionization source combining vacuum ultraviolet photoionization and chemical ionization for mass spectrometry analysis; Chinese invention patent (201711204824.0) discloses a combined photoionization and chemical ionization ionization source. These patents utilize photoionization or photoelectron ionization to obtain reagent ions, which then ionize sample molecules through chemical ionization. Chemical ionization can overcome the limitations of photon energy, effectively ionizing molecules with ionization energies higher than the photon energy. Chemical ionization requires the generation of sufficiently strong reagent ions to effectively ionize sample molecules. However, excessively strong reagent ions can cause numerous problems: on the one hand, the space charge effect caused by Coulomb repulsion between reagent ions can lead to a decrease in mass spectrometry resolution, sensitivity, and quantitative capability; on the other hand, excessively strong reagent ions can damage the ion detector, shortening its service life.

[0004] The principle of Penning ionization is that when the excitation energy of the metastable atom A* is higher than the ionization energy of the molecule to be measured, the sample molecule can be ionized. Unlike chemical ionization that relies on high-intensity reagent ions, Penning ionization utilizes neutral metastable atoms with high excitation energy, thus effectively avoiding the above-mentioned problems caused by excessively strong reagent ions. However, Penning ionization is currently used in discharge ionization sources, such as direct analysis in real time (DART) and glow discharge mass spectrometry (GD-MS). The present invention introduces Penning ionization into photoionization mass spectrometry to compensate for the defects that the photoionization source can only ionize substances with ionization energy lower than the photon energy and that the chemical ionization reagent ions are too strong. Summary of the Invention

[0005] The present invention provides a photo-induced Penning ionization mass spectrometry method.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A photo-induced Penning ionization mass spectrometry method employs an apparatus including a photoionization source, the photoionization source including an ionization source chamber, the ionization source chamber being a cylindrical structure with left and right ends open, a plate-shaped inlet electrode and an outlet electrode respectively provided at the left and right open ends of the ionization source chamber, the plate-shaped inlet electrode and the outlet electrode being sealedly connected to the end surfaces of the two open ends, the outlet electrode being a vacuum differential electrode;

[0008] A circular photoelectron emitting electrode is provided in the middle of the ionization source chamber, and the photoelectron emitting electrode is coaxial with the ionization source chamber;

[0009] A through hole serving as a light inlet is radially provided on the sidewalls (e.g., the upper sidewall) of the ionization source chamber and the annular photoelectron emitting electrode. Light emitted from the vacuum ultraviolet light source passes through the radial direction of the light inlet photoelectron emitting electrode and is incident on the interior of the region surrounded by the photoelectron emitting electrode.

[0010] A sample gas inlet, or a sample gas inlet and a background gas inlet are provided on the upper edge of the side wall of the ionization source chamber between the inlet electrode and / or the inlet electrode and the photoelectron emission electrode;

[0011] An exhaust port is provided on the upper edge of the side wall of the ionization source chamber between the outlet electrode and / or the outlet electrode and the photoelectron emission electrode; the characteristics are:

[0012] The gas introduced into the ionization source chamber through the sample gas inlet, or the sample gas inlet and the background gas inlet, is one or more gases selected from the group consisting of helium, neon, and argon.

[0013] The number density of gas molecules in the ionization source chamber is N, which ranges from (2 to 20)×10 16 cm -3 , preferably (2.83~12.1)×10 16 cm -3 The electric field strength between the entrance electrode and the photoelectron emission electrode is E, and the range of E / N is (2 to 20)×10 - 16 Vcm 2 , preferably (3.5~15)×10 -16 Vcm 2 .

[0014] Furthermore, in the above technical solution, the entrance electrode is a plate-shaped repeller electrode, the right side of which is sealed and connected to the left open end face of the ionization source chamber; the exit electrode is a vacuum differential electrode, which is a plate-shaped electrode with a truncated cone-shaped through hole with a trapezoidal axial cross-section in the middle, and the upper bottom surface of the truncated cone of the truncated cone through hole (the bottom surface on the side with the smaller area) is close to the entrance electrode, and the left side surface is sealed and connected to the right open end face of the ionization source chamber;

[0015] A mass analyzer is provided outside the ionization source cavity and at a truncated cone-shaped through hole close to the exit electrode, with the through hole facing the sample inlet of the mass analyzer;

[0016] The vacuum port is connected to the gas inlet of the vacuum pump through a pipeline, which is used to maintain the vacuum in the ionization source cavity; a vacuum gauge for measuring the air pressure in the ionization source cavity is provided at the vacuum port.

[0017] Furthermore, in the above technical solution, the molecular number density N is calculated according to the following formula, where p is the pressure of the ionization region, N A is Avogadro's constant, R is the ideal gas constant, and T is the temperature of the ionization region. The ionization region usually refers to the area between the entrance electrode and the photoelectron emission electrode. The gas pressure in the ionization region usually refers to the gas pressure in the ionization source chamber.

[0018]

[0019] Furthermore, in the above technical solution, the photoelectron emitting electrode is made of metal or alloy (such as stainless steel), and when the vacuum ultraviolet light source irradiates the photoelectron emitting electrode, photoelectrons will escape due to the photoelectric effect.

[0020] Furthermore, in the above technical solution, the vacuum ultraviolet light source is a gas discharge lamp, an ultraviolet light-emitting diode, a synchrotron radiation light source or a laser light source; the mass analyzer is at least one or more of a magnetic mass analyzer, a quadrupole mass analyzer, an ion trap mass analyzer, a time-of-flight (TOF) mass analyzer, a Fourier transform ion cyclotron resonance (FT-ICR) mass analyzer, and an electrostatic field orbitrap (Orbitrap) mass analyzer.

[0021] Furthermore, in the above technical solution, the background gas introduced into the ionization source chamber through the background gas inlet is a gas containing one or more of helium, neon, and argon. When the sample gas introduced into the ionization source chamber through the sample gas inlet contains one or more of helium, neon, and argon, the background gas inlet and / or background gas can be omitted.

[0022] Furthermore, in the above technical solution, the sample gas introduced into the ionization source chamber from the sample gas inlet is a gas containing the sample gas to be tested. The sample to be tested can be a single gas or a mixed gas. The ionization energy of the sample to be tested can be lower than the photon energy or higher than or equal to the photon energy. Samples to be tested with higher ionization energy include some inorganic substances, alkanes, halogenated hydrocarbons, acids, nitriles, etc., such as carbon dioxide and sulfur dioxide, alkanes such as methane, halogenated hydrocarbons such as monochloromethane, dichloromethane, trichloromethane, and tetrachloromethane, and nitriles such as acetonitrile; samples to be tested with lower ionization energy include some inorganic substances, alcohols, ethers, (halogenated) alkenes, (halogenated) alkynes, aldehydes, ketones, acyl halides, acid anhydrides, enones, esters, amides, amines, benzene series and their derivatives, such as toluene.

[0023] Beneficial effects

[0024] The present invention utilizes photoelectrons generated by the photoelectric effect to accelerate in an electric field to obtain sufficient energy to excite ground-state helium (He), neon (Ne), and argon (Ar) atoms to a metastable state. The metastable energy of these neutral atoms is higher than 10.6 eV (He excitation energy is 20.62 and 19.82 eV; Ne excitation energy is 16.72 eV and 16.62 eV; Ar excitation energy is 11.72 eV and 11.55 eV). Penning ionization can be used to ionize sample molecules whose ionization energy is higher than the photon energy and which cannot be ionized by traditional photoionization. This avoids the space charge effect caused by excessive Coulomb repulsion between reagent ions during ion transmission, which leads to a decrease in mass spectrometric resolution, sensitivity, and quantitative capability, as well as damage to the ion detector caused by excessive reagent ions. For sample molecules whose ionization energy is lower than the photon energy and which can be ionized by traditional photoionization, such as toluene, the sensitivity can be increased by about 5 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings further illustrate the present invention, but the contents in the accompanying drawings do not constitute any limitation to the present invention.

[0026] Figure 1 The present invention provides a photo-induced Penning ionization mass spectrometry method and application.

[0027] In the figure, 1. Sample gas inlet; 2. Background gas inlet; 3. Inlet electrode; 4. Ionization region; 5. Vacuum ultraviolet light source; 6. Photoelectron emission electrode; 7. Vacuum pump; 8. Outlet electrode;

[0028] Figure 2 The mass spectra of Example 1 under different background gases (balance gases) are shown below:

[0029] Figure 3 The mass spectra of Example 1 at different E / N are shown below:

[0030] Figure 4 is the mass spectrum of Example 2;

[0031] Figure 5 This is the mass spectrum of Example 3. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0037] In the description of the present invention, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0038] Example 1

[0039] See also Figure 1, which is a photo-induced Penning ionization mass spectrometry method of the present invention.

[0040] A photo-induced Penning ionization mass spectrometry method employs an apparatus including a photoionization source, wherein the photoionization source includes an ionization source chamber, the ionization source chamber being a cylindrical structure with left and right ends open, and a plate-shaped inlet electrode 3 and an outlet electrode 8 being respectively provided at the left and right open ends of the ionization source chamber, the plate-shaped inlet electrode 3 and the outlet electrode 8 being sealedly connected to the end faces of the two open ends, wherein the outlet electrode 8 is a vacuum differential electrode;

[0041] A circular photoelectron emitting electrode 6 is provided in the middle of the ionization source chamber, and the photoelectron emitting electrode 6 is coaxial with the ionization source chamber;

[0042] A through hole serving as a light inlet is radially provided on the side wall (e.g., the upper side wall) of the ionization source chamber and the annular photoelectron emission electrode 6. The light emitted by the vacuum ultraviolet light source 5 passes through the radial direction of the light inlet photoelectron emission electrode 6 and is emitted into the area surrounded by the photoelectron emission electrode 6.

[0043] A sample gas inlet 1, or a sample gas inlet 1 and a background gas inlet 2, is provided on the entrance electrode 3 and / or on the upper edge of the side wall of the ionization source chamber between the entrance electrode 3 and the photoelectron emission electrode 6;

[0044] An exhaust port is provided on the upper edge of the side wall of the ionization source chamber between the outlet electrode 8 and / or the outlet electrode 8 and the photoelectron emission electrode 6; the characteristics are:

[0045] The gas introduced into the ionization source chamber through the sample gas inlet 1, or the sample gas inlet 1 and the background gas inlet 2, is one or more gases selected from the group consisting of helium, neon, and argon.

[0046] The number density of gas molecules in the ionization source chamber is N, which ranges from (2 to 20)×10 16 cm -3 , preferably (2.83~12.1)×10 16 cm -3 The electric field strength between the entrance electrode 3 and the photoelectron emission electrode 6 is E, and the range of E / N is (2 to 20)×10 - 16 Vcm 2 , preferably (3.5~15)×10 -16 Vcm 2 .

[0047] The entrance electrode 3 is a plate-shaped repeller electrode, the right side of which is tightly connected to the left open end of the ionization source chamber;

[0048] The outlet electrode 8 is a vacuum differential electrode, which is a plate-shaped electrode with a truncated cone-shaped through hole with a trapezoidal axial cross-section in the middle. The upper bottom surface of the truncated cone-shaped through hole (the bottom surface with a smaller area) is close to the inlet electrode 3, and its left side surface is sealed with the right open end surface of the ionization source cavity.

[0049] A mass analyzer is provided outside the ionization source cavity and at a truncated cone-shaped through hole near the exit electrode 8, with the through hole facing the sample inlet of the mass analyzer;

[0050] The gas extraction port is connected to the gas inlet of the vacuum pump 7 through a pipeline, and is used to maintain the vacuum in the ionization source cavity; a vacuum gauge for measuring the air pressure in the ionization source cavity is provided at the gas extraction port.

[0051] The ionization region 4 generally refers to the region between the entrance electrode 3 and the photoelectron emission electrode 6 , and the gas pressure in the ionization region 4 generally refers to the gas pressure in the ionization source chamber;

[0052] The light emitted by the vacuum ultraviolet light source 5 is perpendicular to the axial direction of the photoelectron emission electrode 6. The range of the vacuum ultraviolet light emitted by the vacuum ultraviolet light source 5 inside the photoelectron emission electrode 6 is the ionization zone, which usually refers to the area between the entrance electrode 3 and the photoelectron emission electrode 6. The area between the ionization zone and the exit electrode 8 constitutes the reaction zone; the inner diameter of the ionization source chamber is 0.7 cm; the mass analyzer is a time-of-flight mass analyzer.

[0053] (1) As one embodiment, the sample gas is a mixture of 20 ppmv carbon dioxide (CO2) and 0.8 ppmv chloroform (CHCl3). The balance gas used is high-purity argon (Ar); the background gas is high-purity helium (He). The inlet flow rate of both the sample and background gases is 100 mL / min at atmospheric pressure, equivalent to diluting the sample gas concentration by half. Therefore, the sample gas concentration in ionization region 4 is 10 ppmv carbon dioxide (CO2) and 0.4 ppmv chloroform (CHCl3). The balance gas is a mixture of 50% Ar and 50% He (v / v).

[0054] The vacuum ultraviolet light source 5 is a gas discharge lamp (power 1W), specifically a vacuum ultraviolet krypton lamp, and the emitted photon energy is 10.0 and 10.6 eV, which is lower than the ionization energy of CO2 (13.78 eV) and CHCl3 (11.37 eV). Under the commonly used nitrogen balance gas, no signals of CO2 and CHCl3 are detected.

[0055] The photoelectron emission electrode 6 is made of stainless steel. When the vacuum ultraviolet light source 5 irradiates the photoelectron emission electrode 6 , photoelectrons escape from the photoelectron emission electrode 6 due to the photoelectric effect.

[0056] The voltage applied to the entrance electrode 3 is 74 V, the voltage applied to the photoelectron emission electrode 6 is 23.1 V, and the distance between the entrance electrode 3 and the photoelectron emission electrode 6 is 1.2 cm. The electric field intensity E in the ionization zone (i.e., the electric field intensity between the entrance electrode 3 and the photoelectron emission electrode 6) is:

[0057]

[0058] The photoelectrons emitted from the photoelectron emission electrode 6 carry a negative charge and therefore move toward the entrance electrode 3 with a high potential, are accelerated in the electric field, and gain energy, thereby exciting the equilibrium gas in the ionization region 4 to a metastable state.

[0059] The pressure p of the ionization region 4 (i.e., the pressure in the ionization source chamber) is 500 Pa, the temperature T of the ionization region 4 is 363.15 K, and the Avogadro constant N is A =6.02214179…×10 23 mol -1 , here we take 6.02×10 23 mol -1 Ideal gas constant R = 8.314459…J mol -1 K -1 , here we take 8.314 J mol -1 K -1 , then the molecular number density N (i.e. the gas molecule number density in the ionization source chamber) is:

[0060]

[0061]

[0062] The mass spectrum obtained is as follows Figure 2 As shown by the top line in .

[0063] (II) As a comparative example, the process and conditions are the same as those in step (I) above, except that high-purity argon Ar (instead of high-purity helium He) is used as the background gas, and the ionization region 4 is filled with pure Ar (as the background gas or balance gas); the mass spectrum obtained is as follows: Figure 2 As shown by the lines in the middle.

[0064] (III) As another embodiment, the process and conditions are the same as those described in step (I) above, except that the sample gas is a mixture of 10 ppmv carbon dioxide CO2 and 0.4 ppmv chloroform CHCl3, the balance gas is high-purity nitrogen N2 (replacing the sample gas in step (I)), and no background gas is introduced. The mass spectrum obtained is as follows: Figure 2 As shown by the bottom line.

[0065] The excitation energy of different background gases and the ionization energy of each sample are shown in Table 1. The mass spectra obtained are as follows: Figure 2 shown.

[0066] The excitation energy of nitrogen N2 (8.55 and 6.17 eV) is lower than the ionization energy of CO2 (13.78 eV) and CHCl3 (11.37 eV), so under pure N2 balance gas, CO2 and CHCl3 cannot be detected;

[0067] The excitation energy of argon (11.72 and 11.55 eV) is lower than the ionization energy of CO2 (13.78 eV) and higher than the ionization energy of CHCl3 (11.37 eV). Therefore, under pure Ar balance gas, CO2 cannot be detected, but CHCl3 can be detected.

[0068] The excitation energy of helium (He) (20.61 and 19.82 eV) is higher than the ionization energy of CO2 (13.78 eV) and CHCl3 (11.37 eV). Therefore, under the balance gas of 50% He + 50% Ar, both CO2 and CHCl3 can be detected with good sensitivity.

[0069] (IV) As another comparative example, except that the different gas pressure p in the ionization region 4 leads to different molecular number density N, and thus different E / N, other processes and conditions are the same as those described in the above step (I).

[0070] Specifically, the difference from step (1) is that:

[0071] E / N is not (2 to 20) × 10 as defined in claim 1 of this patent. -16 Vcm 2 , there are two cases:

[0072] First, E / N < 2 × 10 -16 Vcm 2 , the energy obtained by the electrons is insufficient to excite Ar and He to excited states, so CO2 and CHCl3 cannot be detected;

[0073] Specifically, when the gas pressure in the ionization zone is 2000Pa (other processes and conditions are the same as those described in step (1) above),

[0074]

[0075]

[0076] Second, E / N>20×10 -16 Vcm 2The energy obtained by the electrons is too high, producing extremely strong equilibrium gas ions, which will cause the space charge effect caused by the excessive Coulomb repulsion between ions during ion transmission, resulting in a decrease in mass spectrometry resolution, sensitivity and quantitative ability, as well as damage to the ion detector caused by excessive ions.

[0077] Specifically, when the pressure in the ionization zone is 35 Pa (other processes and conditions are the same as those in step (1) above),

[0078]

[0079]

[0080] Mass spectra at different E / N levels are shown below: Figure 3 The concentrations of the sample gas in the ionization region 4 are 10 ppmv CO2 and 0.4 ppmv CHCl3, and the balance gas is a mixture of 50% Ar and 50% He (v / v). Figure 3 (a) is the full mass spectrum, Figure 3 (b) is a partial magnified mass spectrum of characteristic ions of CO2 and CHCl3. E / N = 4.25 × 10 -16 Vcm 2 In the (2~20)×10 -16 Vcm 2 When the range is within 200 nm, CO2 and CHCl3 have the highest sensitivity, and there are no excessively strong equilibrium gas ions (such as Ar + ) brought about by the above-mentioned negative impacts.

[0081] Example 2

[0082] The process and conditions are the same as those in step (1) of Example 1, except that:

[0083] (1) The gas pressure p in the ionization zone 4 is 300 Pa (other processes and conditions are the same as those described in step (1) of Example 1).

[0084]

[0085]

[0086] (2) The air pressure p in the ionization zone 4 is 150 Pa,

[0087]

[0088]

[0089] The N and E / N of Example 2 (I) and (II) are both within the scope of claim 1 of this patent and are also within the preferred range. The mass spectra obtained are as follows: Figure 4As shown in the lower and upper lines, both CO2 and CHCl3 can be detected with high sensitivity.

[0090] Example 3

[0091] The process and conditions were the same as those described in step (1) of Example 1, except that the sample gas was 1 ppmv toluene C7H8 (ionization energy 8.83 eV), the balance gas was high-purity argon Ar or high-purity nitrogen N2 (replacing the sample gas in step (1)), and no background gas was introduced.

[0092] The air pressure p in the ionization zone 4 is 300 Pa.

[0093]

[0094]

[0095] The mass spectrum obtained is as follows Figure 5 As shown. The balance gas is high purity argon Ar ( Figure 5 The balance gas is high purity nitrogen N2 ( Figure 5 The sensitivity of the method is about 5 times higher than that of the conventional photoionization method. This shows that the method of the present invention can not only ionize high ionization energy substances that cannot be ionized by conventional photoionization, but also further enhance the sensitivity of low ionization energy substances that can be ionized by conventional photoionization.

[0096] Table 1

[0097]

[0098] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are intended solely to illustrate the principles of the present invention and are not to be construed in any way as limiting the scope of protection of the present invention. Based on the explanations herein, those skilled in the art will be able to devise other specific embodiments of the present invention without inventive effort, and such equivalent variations or substitutions are intended to be encompassed within the scope of the claims of this application.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photo-induced Penning ionization mass spectrometry method, wherein the device comprises a photoionization source, wherein the photoionization source comprises an ionization source chamber, wherein the ionization source chamber is a cylindrical structure with left and right ends open, wherein an inlet electrode (3) and an outlet electrode (8) are respectively provided at the left and right open ends of the ionization source chamber and are sealedly connected to the end faces of the two open ends, wherein the outlet electrode (8) is a vacuum differential electrode; A circular photoelectron emitting electrode (6) is provided in the middle of the ionization source chamber, and the photoelectron emitting electrode (6) is coaxial with the ionization source chamber; A through hole serving as a light inlet is provided along the radial direction of the side wall surface (e.g., the upper side wall) of the ionization source chamber and the annular photoelectron emitting electrode (6), and the emitted light from the vacuum ultraviolet light source (5) passes through the radial direction of the light inlet photoelectron emitting electrode (6) and is emitted into the interior of the area surrounded by the photoelectron emitting electrode (6); A sample gas inlet (1), or a sample gas inlet (1) and a background gas inlet (2) are provided on the sidewall of the ionization source chamber between the inlet electrode (3) and / or the inlet electrode (3) and the photoelectron emission electrode (6); An exhaust port is provided on the upper edge of the side wall of the ionization source chamber between the outlet electrode (8) and / or the outlet electrode (8) and the photoelectron emission electrode (6); the invention is characterized in that: The gas introduced into the ionization source chamber through the sample gas inlet (1), or the sample gas inlet (1) and the background gas inlet (2) contains one or more gases selected from the group consisting of helium, neon, and argon. The number density of gas molecules in the ionization source chamber is N, which ranges from (2 to 20)×10 16 cm -3 , preferably (2.83~12.1)×10 16 cm -3 The electric field strength between the entrance electrode (3) and the photoelectron emission electrode (6) is E, and the range of E / N is (2 to 20) × 10 -16 Vcm 2 , preferably (3.5~15)×10 -16 Vcm 2 .

2. The method according to claim 1, wherein: The entrance electrode (3) is a plate-shaped repeller electrode, the right side of which is tightly connected to the left open end of the ionization source chamber; The outlet electrode (8) is a vacuum differential electrode, which is a plate-shaped electrode with a truncated cone-shaped through hole with a trapezoidal axial cross section in the middle, and the upper bottom surface of the truncated cone of the truncated cone-shaped through hole (the bottom surface on the side with a smaller area) is close to the side of the inlet electrode (3), and the left side surface is sealed and connected to the right open end surface of the ionization source cavity; A mass analyzer is provided outside the ionization source cavity and at a truncated cone-shaped through hole close to the exit electrode (8), with the through hole facing the sample inlet of the mass analyzer; The air extraction port is connected to the gas inlet of a vacuum pump (7) through a pipeline and is used to maintain the vacuum in the ionization source cavity; a vacuum gauge for measuring the gas pressure in the ionization source cavity is provided at the air extraction port of the ionization source cavity.

3. The method according to claim 1 or 2, characterized in that: The molecular number density N is calculated according to the following formula, where p is the pressure in the ionization region (4), N A is Avogadro's constant, R is the ideal gas constant, and T is the temperature of the ionization region (4); the ionization region (4) usually refers to the region between the entrance electrode (3) and the photoelectron emission electrode (6), and the gas pressure of the ionization region (4) usually refers to the gas pressure in the ionization source chamber; 4. The method according to claim 1, wherein: The photoelectron emission electrode (6) is made of metal or alloy, and when the vacuum ultraviolet light source (5) irradiates the photoelectron emission electrode (6), photoelectrons are emitted due to the photoelectric effect.

5. The method according to claim 1 or 2, characterized in that: The vacuum ultraviolet light source (5) is a gas discharge lamp, an ultraviolet light emitting diode, a synchrotron radiation light source or a laser light source; The mass analyzer is at least one or more of a magnetic mass analyzer, a quadrupole mass analyzer, an ion trap mass analyzer, a time-of-flight (TOF) mass analyzer, a Fourier transform ion cyclotron resonance (FT-ICR) mass analyzer, and an electrostatic field orbitrap (Orbitrap) mass analyzer.

6. The method according to claim 1, wherein: The background gas introduced into the ionization source chamber through the background gas inlet (2) contains one or more of helium, neon and argon; and when the sample gas introduced into the ionization source chamber through the sample gas inlet (1) contains one or more of helium, neon and argon, the background gas inlet (2) and / or the background gas can be omitted.

Images