NO2 < + > chemical ionization and vacuum ultraviolet light ionization source device

Abstract

The invention relates to a mass spectrometry instrument, in particular to a chemical ionization and vacuum ultraviolet light ionization source device for NO < 2 + >. Comprising a vacuum ultraviolet lamp, an ionization chamber cavity, a discharge electrode, a differential hole electrode and an ion transmission electrode group, the discharge electrode, the ion transmission electrode group and the differential hole electrode are coaxially arranged in the ionization chamber cavity, and the vacuum ultraviolet lamp is arranged at an ultraviolet light inlet above the ionization chamber cavity; a through hole is formed in the wall surface of the bottom of the ionization chamber cavity, and the differential hole electrode is arranged above the through hole; a reagent gas sample introduction capillary tube and a sample gas sample introduction capillary tube are arranged on the side wall of the ionization chamber cavity; different direct-current voltages are applied to a lamp electrode and a discharge electrode of the vacuum ultraviolet lamp, discharge is generated between the vacuum ultraviolet lamp and the discharge electrode through voltage difference, and reagent ions are obtained. Discharge can be generated between the vacuum ultraviolet lamp and the discharge electrode, high-concentration NO2 < + > reagent ions are obtained, and then the NO2 < + > reagent ions and sample molecules are subjected to ion and molecule chemical ionization reaction.

Description

Technical Field

[0001] The present invention relates to a mass spectrometer, in particular to a NO2 + Chemical ionization and vacuum ultraviolet photoionization source devices. Background Art

[0002] Vacuum ultraviolet photoionization (VUV-PI) is a threshold photoionization technique that directly ionizes a substance molecule by absorbing VUV photons with photon energy greater than its ionization energy (IE). It has a high molecular ion yield and low fragmentation, and is an efficient mass spectrometry "soft" ionization technique. Inert gas discharge lamps are commonly used as VUV light sources in photoionization mass spectrometry, such as krypton (Kr) discharge lamps. Compared with large synchrotron radiation sources and lasers, VUV lamps have the advantages of small size, low cost, low power consumption, and easy operation and maintenance. However, due to the limitation of the light window material, the lithium fluoride material that can currently transmit the highest photon energy can only transmit VUV photons with an energy of no more than 11.8eV, while the commonly used Kr lamp emits a photon energy of only 10.6eV at most. For some high ionization energy compounds, such as acetonitrile (IE = 12.20eV) and formaldehyde (IE = 10.88eV), it cannot be effectively ionized, which limits the application range of photoionization mass spectrometry. Chemical ionization (CI) is a "soft" ionization technique that ionizes the molecules of the test compound through ion-molecule reactions. It uses reactions such as proton transfer (PTR), charge transfer (CE), and electrophilic addition (EA) between reagent ions and sample molecules to obtain molecular ions or quasi-molecular ions of the test compound. For example, formaldehyde can be ionized by reacting with hydronium ions (H3O + ) are effectively ionized by the PTR reaction between them to produce protonated ions of formaldehyde. Combining vacuum ultraviolet photoionization and chemical ionization, and using different ionization modes for compound molecules with different characteristics, can effectively improve the ionization efficiency and broaden the application range of online mass spectrometers. Summary of the invention

[0003] In view of the above problems, the present invention aims to provide a NO2 + Chemical ionization and vacuum ultraviolet photoionization source devices.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] The present invention provides a NO2 +The invention discloses a chemical ionization and vacuum ultraviolet photoionization source device, comprising a vacuum ultraviolet lamp, an ionization chamber cavity, a discharge electrode, a differential aperture electrode and an ion transmission electrode group, wherein the discharge electrode, the ion transmission electrode group and the differential aperture electrode are coaxially arranged in the ionization chamber cavity, and the vacuum ultraviolet lamp is arranged at the ultraviolet light entrance above the ionization chamber cavity; a through hole is arranged on the bottom wall of the ionization chamber cavity, the differential aperture electrode is arranged above the through hole, and the differential aperture electrode is grounded through a resistor; a reagent gas injection capillary and a sample gas injection capillary located below the reagent gas injection capillary are arranged on the side wall of the ionization chamber cavity; different DC voltages are applied to the lamp electrode and the discharge electrode of the vacuum ultraviolet lamp, and the voltage difference between the vacuum ultraviolet lamp and the discharge electrode causes discharge between the vacuum ultraviolet lamp and the discharge electrode, the reagent gas is ionized, and reagent ions are obtained, and ion and molecular chemical ionization reactions occur between the reagent ions and the sample molecules.

[0006] The ion transport electrode group includes more than three ion transport electrodes, each of which is a circular flat plate structure with a circular through hole in the middle. The more than three ion transport electrodes are coaxially and parallelly arranged from top to bottom, and each adjacent two ion transport electrodes are connected by a resistor with the same resistance value.

[0007] The gas outlet of the reagent gas injection capillary is located between two adjacent ion transmission electrodes at the top layer; and the gas outlet end of the reagent gas injection capillary is perpendicular to the ultraviolet light beam.

[0008] Different voltages are sequentially loaded on the discharge electrode, ion transport electrode and differential aperture electrode in the order from high to low, so as to divide the ionization zone into three zones: a photoionization zone, a reagent ion generation zone and a sample molecule reaction zone.

[0009] The gas outlet of the sample gas injection capillary is located at the top of the sample molecule reaction zone; the gas outlet end of the sample gas capillary is perpendicular to the ultraviolet light beam.

[0010] The diameter of the middle through hole of the ion transport electrode and the differential aperture electrode is 2-20 mm; the distance between the ion transport electrode and the differential aperture electrode is 20-200 mm.

[0011] The reagent gas injection capillary and the sample gas injection capillary are both metal capillaries, PEEK capillaries or quartz capillaries, and have a length of 0.05-5m and an inner diameter of 25-500μm.

[0012] The ultraviolet light source generated by the vacuum ultraviolet lamp is a rare gas glow discharge light source. Ultraviolet light of different intensities can be obtained by changing the DC voltage applied to the lamp electrode; the discharge degree can be changed by changing the applied DC voltage to generate reagent ions of different concentrations.

[0013] A mass analyzer is arranged below the differential aperture electrode, and the ions generated by the ionization chamber cavity enter the mass analyzer through the small holes of the differential aperture electrode.

[0014] The mass analyzer is a time-of-flight mass analyzer, a quadrupole mass analyzer or an ion trap mass analyzer.

[0015] The vacuum ultraviolet light source is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source.

[0016] The advantages and beneficial effects of the present invention are: the present invention provides a NO2 + The chemical ionization and vacuum ultraviolet photoionization source device uses the ultraviolet light emitted by the vacuum ultraviolet lamp to directly ionize the sample molecules with single photons to obtain the molecular ions or quasi-molecular ions of the sample. At the same time, discharge can be generated between the vacuum ultraviolet lamp and the adjacent discharge electrode below it to obtain high-concentration NO2 + The reagent ions then undergo chemical ionization reactions with the sample molecules, thereby broadening the types of ionizable analytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a NO2 + Schematic diagram of the structure of the chemical ionization and vacuum ultraviolet photoionization source device;

[0018] In the figure: 1-vacuum ultraviolet lamp; 2-discharge electrode; 3-ion transport electrode; 4-differential aperture electrode; 5-reagent gas injection capillary; 6-sample gas injection capillary; 7-ionization chamber cavity.

[0019] Figure 2 This is the characteristic spectrum of n-pentane to n-undecane in the embodiment of the present invention;

[0020] Figure 3 It is a quantitative curve diagram of n-pentane to n-undecane in the embodiment of the present invention;

[0021] Figure 4 It is a daytime repeatability graph of 10 ppbv and 1000 ppbv n-nonane in the examples of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] See also Figure 1 As shown, the present invention provides a NO2 +The invention discloses a chemical ionization and vacuum ultraviolet photoionization source device, comprising a vacuum ultraviolet lamp 1, a discharge electrode 2, an ionization chamber cavity 7, a differential aperture electrode 4 and an ion transmission electrode group, wherein the discharge electrode 2, the ion transmission electrode group and the differential aperture electrode 4 are coaxially arranged in the ionization chamber cavity 7 in sequence, the vacuum ultraviolet lamp 1 is arranged above the ionization chamber cavity 7, an ultraviolet light inlet is provided on the wall of the ionization chamber cavity 7 above the through hole of the discharge electrode 2, and the corresponding vacuum ultraviolet lamp 1 is arranged at the ultraviolet light inlet; a through hole is provided on the bottom wall of the ionization chamber cavity 7, and the differential aperture electrode 4 is arranged above the through hole. , and the differential aperture electrode 4 is grounded through a resistor; a reagent gas injection capillary 5 and a sample gas injection capillary 6 located below the reagent gas injection capillary 5 are provided on the side wall of the ionization chamber cavity 7; different DC voltages are applied to the lamp electrode, the discharge electrode 2, the ion transmission electrode group, and the differential aperture electrode 4 of the vacuum ultraviolet lamp 1, and the voltage difference between the vacuum ultraviolet lamp 1 and the discharge electrode 2 causes a discharge to be generated between the vacuum ultraviolet lamp 1 and the discharge electrode 2, the reagent gas is ionized, and reagent ions are obtained, and ion and molecular chemical ionization reactions occur between the reagent ions and the sample molecules.

[0024] See also Figure 1 As shown, in an embodiment of the present invention, the ion transport electrode group includes more than three ion transport electrodes 3, each ion transport electrode 3 is a circular flat plate structure with a circular through hole in the middle, and the more than three ion transport electrodes 3 are coaxially and parallelly arranged from top to bottom, and each two adjacent ion transport electrodes 3 are connected by a resistor with the same resistance value.

[0025] Preferably, the diameter of the middle through hole of the ion transport electrode 3 and the differential aperture electrode 4 is 2-20 mm; and the distance between the ion transport electrode 3 and the differential aperture electrode 4 is 20-200 mm.

[0026] Specifically, the gas outlet of the reagent gas injection capillary 5 is located between the discharge electrode and the adjacent ion transmission electrode; the gas outlet end of the reagent gas injection capillary 5 is perpendicular to the ultraviolet beam. The gas outlet of the sample gas injection capillary 6 is located at the top of the sample molecule reaction area; the gas outlet end of the sample gas injection capillary 6 is perpendicular to the ultraviolet beam.

[0027] Preferably, the reagent gas injection capillary 5 and the sample gas injection capillary 6 are both metal capillaries, PEEK capillaries or quartz capillaries, and have a length of 0.05-5 m and an inner diameter of 25-500 μm.

[0028] Furthermore, different voltages are sequentially loaded on the discharge electrode 2, the ion transport electrode 3, and the differential aperture electrode 4 in the order from high to low, so as to divide the ionization zone into three zones: a photoionization zone, a reagent ion generation zone, and a sample molecule reaction zone.

[0029] In the embodiment of the present invention, the ultraviolet light source generated by the vacuum ultraviolet lamp 1 is a rare gas glow discharge light source. Ultraviolet light of different intensities can be obtained by changing the DC voltage applied to the lamp electrodes; the discharge degree can be changed by changing the applied DC voltage to generate reagent ions of different concentrations.

[0030] Further, a mass analyzer is provided below the differential aperture electrode 4, and the ions generated by the ionization chamber cavity 7 enter the mass analyzer through the small hole of the differential aperture electrode 4. The mass analyzer is a time-of-flight mass analyzer, a quadrupole mass analyzer or an ion trap mass analyzer. The vacuum ultraviolet light source is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source.

[0031] Example

[0032] For the NO2 + The chemical ionization and vacuum ultraviolet photoionization source device performance was examined. A mixture of nitrogen and oxygen was introduced into the reagent gas sampling capillary 5, and 1ppm of n-pentane to n-undecane with air as the balance gas was introduced into the sample gas sampling capillary 6. The above ionization source was used for detection and analysis, and quantitative analysis and daytime stability analysis were performed. The vacuum ultraviolet lamp 1 used was a commercial Kr lamp, and the maximum photon energy emitted was 10.6eV. The DC voltage applied to the lamp electrode was 1400V, the DC voltage applied to the discharge electrode 2 was 500V, the DC voltage applied to the ion transmission electrode 3 adjacent to the discharge electrode 2 was 100V, the DC voltage applied to the middle ion transmission electrode 3 of the ion transmission electrode group was 9V, and the DC voltage applied to the last ion transmission electrode 3 was 8.5V. The ion transmission electrodes were connected with a 1MΩ resistor. The total length of the ionization source is 64 mm, of which the photoionization region is 5 mm, the reagent ion generation region and the sample molecule reaction region are 59 mm, the mass analyzer is a time-of-flight mass analyzer, the gas pressure in the ionization region is maintained at 230 Pa, and the sample gas injection capillary 6 uses a PEEK capillary with a length of about 46 cm and an inner diameter of 250 μm. The test was performed 5 times in parallel, with an accumulation time of 60 s each time.

[0033] Table 1 Spectral peak signal intensity and relative abundance ratio of main peak of n-pentane to n-undecane standard gas:

[0034]

[0035]

[0036] like Figure 2 As shown in Table 1, the main peaks of n-pentane to n-undecane are [MH] + In addition to the molecular ions and quasi-molecular ions ([M] + +[MH] +) relative strength ratio is lower than 60%, and the rest are all above 60%. Figure 3 As shown in the figure, within the concentration range of n-pentane to n-undecane, the signal intensity and concentration show a good linear relationship, and the linear correlation coefficient is greater than 0.99. The linear range of n-pentane to n-undecane is 10-1000 ppbv. Figure 4 As shown, on the first, second and fifth days, by analyzing 10 ppbv and 1000 ppbv n-decane samples under the same experimental conditions, the relative standard deviations (RSDs) of the peak intensity of the main peak (m / z 141) were 3.46% and 1.74%, respectively. It can be seen that this method has good day-to-day repeatability.

[0037] It can be seen that the composite ionization source device can not only realize single-photon ionization of material molecules with ionization energy lower than the energy of ultraviolet photons, but also realize single-photon ionization of material molecules with ionization energy higher than the energy of ultraviolet photons with NO2 + It is the chemical ionization of reagent ions, thus broadening the types and range of ionizable analytical substances.

[0038] The present invention provides a NO2 + The chemical ionization and vacuum ultraviolet photoionization source device uses a vacuum ultraviolet lamp to ionize a mixture of high-purity oxygen and high-purity nitrogen to generate high-concentration NO2 + Reagent ions, reagent ions and sample molecules undergo molecular and ion reactions, which can achieve ionization analysis of a wide range of analytes, and can more accurately and effectively perform qualitative and identification of unknown samples based on the obtained characteristic spectra.

[0039] The above description is only an embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, expansion, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A NO2 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The invention comprises a vacuum ultraviolet lamp (1), a discharge electrode (2), a differential aperture electrode (4), an ion chamber cavity (7) and an ion transmission electrode group, wherein the discharge electrode (2), the ion transmission electrode group and the differential aperture electrode (4) are coaxially arranged in the ion chamber cavity (7), and the vacuum ultraviolet lamp (1) is arranged at the ultraviolet light entrance above the ion chamber cavity (7); a through hole is arranged on the bottom wall of the ion chamber cavity (7), the differential aperture electrode (4) is arranged above the through hole, and the differential aperture electrode (4) is grounded via a resistor; and a through hole is arranged on the bottom wall of the ion chamber cavity (7). ) is provided with a reagent gas injection capillary (5) and a sample gas injection capillary (6) located below the reagent gas injection capillary (5) on the side wall; different DC voltages are applied to the lamp electrode of the vacuum ultraviolet lamp (1) and the discharge electrode (2), and the voltage difference between the vacuum ultraviolet lamp (1) and the discharge electrode (2) causes discharge to be generated between the vacuum ultraviolet lamp (1) and the discharge electrode (2), the reagent gas is ionized, reagent ions are obtained, and ion and molecular chemical ionization reaction occurs between the reagent ions and the sample molecules.

2. NO2 according to claim 1 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The ion transport electrode group comprises more than three ion transport electrodes (3), each ion transport electrode (3) is a circular flat plate structure with a circular through hole in the middle, the more than three ion transport electrodes (3) are coaxially and parallelly arranged in sequence from top to bottom, and each two adjacent ion transport electrodes (3) are connected by a resistor with the same resistance value.

3. NO2 according to claim 2 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The gas outlet of the reagent gas injection capillary (5) is located between the discharge electrode and the adjacent ion transmission electrode (3); the gas outlet end of the reagent gas injection capillary (5) is perpendicular to the ultraviolet light beam.

4. NO2 according to claim 2 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that Different voltages are sequentially loaded on the discharge electrode (2), the ion transport electrode (3), and the differential aperture electrode (4) in order from high to low, so as to divide the ionization zone into three zones: a photoionization zone, a reagent ion generation zone, and a sample molecule reaction zone.

5. NO2 according to claim 4 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The gas outlet of the sample gas injection capillary (6) is located at the top of the sample molecule reaction zone; and the gas outlet end of the sample gas capillary (6) is perpendicular to the ultraviolet light beam.

6. NO2 according to claim 2 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The diameter of the intermediate through hole of the ion transmission electrode group and the differential aperture electrode (4) is 2-20 mm; the distance between the ion transmission electrode group and the differential aperture electrode (4) is 20-200 mm.

7. NO2 according to claim 1 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The reagent gas injection capillary (5) and the sample gas injection capillary (6) are both metal capillaries, PEEK capillaries or quartz capillaries, and have a length of 0.05-5 m and an inner diameter of 25-500 μm.

8. NO2 according to claim 1 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The ultraviolet light source generated by the vacuum ultraviolet lamp (1) is a rare gas glow discharge light source. Ultraviolet light of different intensities can be obtained by changing the DC voltage applied to the lamp electrodes; the discharge degree can be changed by changing the applied DC voltage to generate reagent ions of different concentrations.

9. NO2 according to claim 1 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that A mass analyzer is provided below the differential aperture electrode (4), and the ions generated by the ionization chamber cavity (7) enter the mass analyzer through the small holes of the differential aperture electrode (4).

10. NO2 according to claim 1 + The chemical ionization and vacuum ultraviolet photoionization source device is characterized in that The mass analyzer is a time-of-flight mass analyzer, a quadrupole mass analyzer or an ion trap mass analyzer.

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