Chemical ion source based on vacuum ultraviolet light ionization

Abstract

The chemical ion source comprises a shell, an insulating lining, a vacuum ultraviolet lamp and a photolysis cavity, the lower ends of the shell and the insulating lining are open cylinders, and the upper ends of the shell and the insulating lining are provided with through holes for leading out wires; the shell is sleeved outside the insulating lining, and the vacuum ultraviolet lamp is placed in the insulating lining; the photolysis cavity is in a gyro shape, a cylindrical reaction cavity is formed in the photolysis cavity, an air inlet is formed in the side face of the photolysis cavity, and an outlet is formed in the bottom face of the photolysis cavity and communicated with the reaction cavity; an internal thread is arranged on the lower portion of the shell, an external thread is correspondingly arranged on the upper portion of the photolysis cavity, and the shell and the photolysis cavity are fixedly connected in a rotating mode through the threads. The chemical ion source is based on a vacuum ultraviolet light ionization technology, can realize efficient generation of different reagent ions, can be carried on different chemical ionization mass spectrometers, facilitates replacement of a vacuum ultraviolet lamp, and is very convenient and rapid to use.

Description

Technical Field

[0001] The utility model relates to the technical field of chemical ionization mass spectrometry detection, in particular to a chemical ion source for chemical ionization mass spectrometry, which can be applied to iodine ion (I - ) and then used in chemical ionization mass spectrometry. Background Art

[0002] The ion source is a key component of chemical ionization mass spectrometry and is the place where reagent ions are generated. - ) as an example, traditional generation methods include radioactive element generation method, X-ray excitation method, electric field excitation method, etc. Radioactive element generation method requires the use of radioactive isotopes (usually 210 Po), the substances used are toxic and strictly controlled, and their use is basically restricted in China. The X-ray excitation method and the electric field excitation method have low efficiency and more mass spectrometry interference, and cannot be applied to the measurement of extremely low concentration species in the atmosphere. In 2020, Yi Ji et al. proposed using a small krypton (Kr) lamp as an ion source and using vacuum ultraviolet (VUV) photoionization of methyl iodide (CH3I) gas to obtain reagent ions I - (Atmos. Meas. Tech., 13, 3683-3696, 2020). This paper provides a direction for subsequent ion source research, but it does not form a complete set of design parameters for VUV ion sources, and the exploration of various interference factors is insufficient. Further theoretical and experimental demonstration is still needed to ultimately achieve a practical technology with universal applicability. Utility Model Content

[0003] The purpose of this utility model is to provide a chemical ion source based on vacuum ultraviolet photoionization, which can not only solve the problems of low efficiency and multiple interferences of traditional X-ray and electric field excitation methods, but also improve the ion source design of the VUV method based on theoretical and experimental research, so that it can be carried on the molecular ion reaction chamber of commercial instruments, realize the efficient generation of reagent ions, and be convenient and quick to use.

[0004] To achieve the above-mentioned purpose, the utility model designs a chemical ion source based on vacuum ultraviolet photoionization for chemical ionization mass spectrometry, comprising an outer shell, an insulating lining, a vacuum ultraviolet lamp and a photolysis chamber, wherein the outer shell and the insulating lining are both cylindrical with an open lower end and a through hole provided at the upper end for leading out the electric wires; the outer shell is sleeved on the outer side of the insulating lining, and the vacuum ultraviolet lamp is placed in the insulating lining; the photolysis chamber has a gyroscope-like appearance and a cylindrical reaction cavity inside, an air inlet is provided on the side of the photolysis chamber, and an outlet is provided on the bottom surface to communicate with the reaction cavity; an internal thread is provided on the lower part of the outer shell, and an external thread is provided on the upper part of the photolysis chamber, and the outer shell and the photolysis chamber are fixedly connected by rotating the thread.

[0005] The chemical ion source of the present invention has an overall columnar structure, wherein the material of the insulating lining is preferably Peek (polyetheretherketone), PFA (soluble polytetrafluoroethylene), etc., and the power cord of the vacuum ultraviolet lamp passes through the through hole of the insulating lining and the upper end of the outer shell; the vacuum ultraviolet lamp is preferably a krypton lamp, and its bottom has a protruding outer edge, and correspondingly, a matching groove is provided at the bottom end of the inner wall of the insulating lining.

[0006] Furthermore, the photolysis chamber can be made of a variety of materials, such as stainless steel, Teflon, Peek, etc., preferably 304 stainless steel or 316 stainless steel. Preferably, the reaction cavity inside the photolysis chamber is a cylindrical cavity with an inner diameter of 10-14 mm and a height of 15-45 mm.

[0007] Furthermore, the inner diameter of the gas inlet located on the side of the photolysis chamber ranges from 0.5 to 2 mm, and the optimal inner diameter is 2 mm to avoid the aggregation of gas molecules to form a large number of polymers.

[0008] Furthermore, a stainless steel pipe with an outer diameter of 1 / 4 inch is provided at the outlet at the bottom of the photolysis chamber, which can be connected to a chemical ionization mass spectrometer.

[0009] Furthermore, the photolysis chamber is connected to a chemical ionization mass spectrometer, which provides a high vacuum environment. The pressure condition of the reaction cavity inside the photolysis chamber is 150-400 mbar. To ensure airtightness, an O-ring is placed between the photolysis chamber and the insulating lining to seal the connection between the two.

[0010] The chemical ion source of this utility model is based on a novel vacuum ultraviolet photoionization technology, which can achieve efficient generation of different reagent ions, including iodide ions, bromide ions, ammonium ions, and other reagent ions. At the same time, it can be installed on different chemical ionization mass spectrometers (only requiring the chemical ionization mass spectrometer to have a 1 / 4-inch stainless steel interface). In addition, considering that vacuum ultraviolet lamps such as krypton lamps generally have a service life of only 3000 hours, when the vacuum ultraviolet lamp reaches the end of its service life, it only needs to be replaced to meet subsequent use needs, which is very convenient and quick. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic structural diagram of the chemical ion source of the present invention, wherein (a) is an appearance diagram, (b) is a longitudinal cross-sectional diagram, and the numbers in the figure represent: 1—housing, 2—insulating lining, 3—photolysis chamber, 4—through hole, 5—krypton lamp, 6—reaction cavity, 7—air inlet, and 8—outlet.

[0012] Figure 2 This is a test diagram of the reagent ion signal intensity of the chemical ion source described in the embodiment of the present invention under conditions of different reaction chamber lengths.

[0013] Figure 3 This is a test chart of the methyl iodide concentration and the reagent ion signal intensity when the chemical ion source described in the embodiment of the present invention is used.

[0014] Figure 4 This is a test diagram of the reagent ion signal intensity under different voltage conditions applied to the photolysis chamber by the chemical ion source described in the embodiment of the utility model when in use. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. The specific embodiments described here are only for explaining the present invention, rather than limiting the present invention.

[0016] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the technical solution of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0017] In addition, the terms “upper”, “lower”, “left”, “right”, “top”, “bottom”, etc. used in the following description are only for the convenience of explaining the structure of the present invention, and are not intended to limit the present invention.

[0018] like Figure 1 As shown, the chemical ion source for chemical ionization mass spectrometry in this embodiment includes a housing 1, an insulating liner 2, a photolysis chamber 3, and a krypton lamp 5, wherein the insulating liner 2 is inserted into the housing 1, an internal thread is provided at the lower portion of the housing 1, and an external thread is provided at the upper portion of the photolysis chamber 3, and the housing 1 and the photolysis chamber 3 are fixedly connected by screw rotation; the krypton lamp 5 is placed in the insulating liner 2, and a through hole 4 is provided at the top of the insulating liner 2 and the housing 1, and the power cord of the krypton lamp 5 is passed through the through hole 4; the photolysis chamber 3 is made of stainless steel, wherein the inner diameter of the reaction cavity 6 is 14 mm, the length of the cavity is 23 mm, an air inlet with an inner diameter of 2 mm is provided on the side of the cavity, and a stainless steel pipe with an outer diameter of 1 / 4 inch is provided at the bottom outlet 8 for connection to the chemical ionization mass spectrometer. It should be noted that the dimensional design and application conditions of this embodiment are optimized by combining theoretical calculations and experimental tests.

[0019] The optimal design parameters and operating conditions of the chemical ion source were obtained through experiments:

[0020] The size and internal structure of the A photolysis chamber will affect the efficiency of reagent ion generation. Since the krypton lamp light source has a diameter of 14mm, the inner diameter of the chamber is fixed at 14mm to ensure that as much methyl iodide as possible is photolyzed in the reaction area. The length of the chamber will affect the residence time. If the chamber is too short, some methyl iodide may not be fully photolyzed, affecting the efficiency of reagent ion generation. If the chamber is too long, some reagent ions may be lost due to collisions during the flow process. Figure 2 The test graph of reagent ion signal intensity under different cavity length conditions. Figure 2 The test results shown above select a solution with higher reagent ion generation under the same conditions and determine the cavity length to be 23 mm.

[0021] The concentration of B methyl iodide standard gas will directly affect the concentration of reagent ions. Within a certain range, the concentration of methyl iodide standard gas should show a linear relationship with the signal intensity of the reagent ions, which means that methyl iodide has been fully photolyzed. Through experimental testing, the concentration of methyl iodide in the range of 100 to 600 ppb shows a very good linear relationship with the signal of the reagent ions, and the linear fitting R 2 Reach 0.998, such as Figure 3 shown.

[0022] Considering that the material of the photolysis chamber is stainless steel, which is conductive, if it is charged by external interference, the negatively charged reagent ions may be lost by hitting the wall, thereby affecting the generation efficiency of the reagent ions. In this regard, the utility model also provides a stable voltage for the ion source. Through experimental tests, such as Figure 4 As shown, it is determined that the ion source used needs to apply a voltage of -5V to the photolysis chamber 3 to ensure the best reagent ion generation efficiency.

Claims

1. A chemical ion source based on vacuum ultraviolet photoionization, comprising a housing, an insulating lining, a vacuum ultraviolet lamp and a photolysis chamber, characterized in that: The outer shell and the insulating lining are both cylindrical and open at the lower end, and are provided with a through hole at the upper end for leading out the wires; the outer shell is sleeved on the outside of the insulating lining, and the vacuum ultraviolet lamp is placed in the insulating lining; the photolysis chamber has a gyroscope-like appearance, and a cylindrical reaction cavity inside, with an air inlet provided on the side of the photolysis chamber and an outlet provided on the bottom surface to communicate with the reaction cavity; an internal thread is provided at the lower part of the outer shell, and an external thread is provided at the upper part of the photolysis chamber accordingly, and the outer shell and the photolysis chamber are fixedly connected by rotating the thread.

2. The chemical ion source according to claim 1, wherein The insulating lining is a cylinder made of Peek or PFA material.

3. The chemical ion source according to claim 1, wherein The top of the insulating lining is provided with a through hole for the power line of the vacuum ultraviolet lamp to pass through, and the bottom end of the inner wall is provided with a groove that matches the protruding edge of the bottom of the vacuum ultraviolet lamp.

4. The chemical ion source according to claim 1, wherein The vacuum ultraviolet lamp is a krypton lamp.

5. The chemical ion source according to claim 1, wherein The photolysis cavity is a cavity made of stainless steel, Teflon or Peek.

6. The chemical ion source according to claim 5, characterized in that The photolysis cavity is made of 304 stainless steel or 316 stainless steel.

7. The chemical ion source according to claim 1, wherein The reaction cavity inside the photolysis chamber is a cylindrical cavity with an inner diameter of 10 to 14 mm and a height of 15 to 45 mm.

8. The chemical ion source according to claim 1, wherein The inner diameter of the air inlet located on the side of the photolysis chamber is 0.5 to 2 mm.

9. The chemical ion source according to claim 1, wherein A stainless steel pipe with an outer diameter of 1 / 4 inch is provided at the outlet located at the bottom of the photolysis chamber.

10. The chemical ion source according to claim 1, wherein An O-ring is placed between the photolysis chamber and the insulating lining.

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