A channel-type VUV ionization source with adjustable ionization region

Abstract

The present invention relates to an ionization source in an analytical instrument, specifically a channel-type VUV ionization source with a controllable ionization region, which includes a hollow circular inner cylinder that transmits vacuum ultraviolet light with two open ends. An outer cylinder made of a hollow circular insulator with two open ends is sleeved outside the inner cylinder. A gap is left between the outer wall surface of the inner cylinder and the inner wall surface of the insulating outer cylinder to form an annular cavity with two open ends. Circular sealing end caps are respectively arranged at the two open ends of the annular cavity, and the circular sealing end caps seal the two open ends of the annular cavity, so that the annular cavity forms a closed annular cylindrical discharge cavity. A discharge gas is filled in the discharge cavity. More than 3 annular discharge electrodes are successively sleeved coaxially outside the outer cylinder, and the more than 3 annular discharge electrodes are respectively connected to an external power source. When this ionization source is combined with a mass spectrometer or an ion mobility spectrometer, it can reduce the discharge voltage, improve the photon utilization rate, and improve the sensitivity.

Description

Technical Field

[0001] The present invention relates to an ionization source in analytical instruments, specifically a novel channel-type high-efficiency VUV ionization source with an adjustable ionization region. Specifically, the length of the discharge region is adjusted by turning on and off different discharge electrodes; the utilization efficiency of photons and the detection sensitivity are improved through the design of a toroidal cylindrical structure combined with a reflective coating, and the channel-type structure is used to make the gas flow smoother and easier to combine with ion mobility spectrometry and mass spectrometry and other plasma detectors. Background Art

[0002] The ionization source is one of the key technologies for plasma-type detection instruments such as mass spectrometry and ion mobility spectrometry. As a novel ionization source, the single-photon ionization source has received increasing attention. It is a soft ionization source that does not produce fragment ions, is easy to analyze the spectrum, and is suitable for the detection and analysis of complex components. In recent years, various ionization sources have been developed based on miniature VUV lamps, such as APPI source, APCI source, DAPI source, etc. The VUV lamp is usually a slender cylindrical structure, and the ultraviolet-transmitting MgF2 light window is located at one end of the cylindrical structure. Since the light generated by the discharge is isotropic, only a small amount of light directly facing the MgF2 light window will pass through the light window and be utilized. Most of the light will be lost. In addition, when the VUV lamp is used in combination with the mobility spectrometry, there are usually two structures: a coaxial structure and a vertical structure. The coaxial structure results in poor gas flow, generates turbulence, and causes residue and affects the sensitivity. The vertical structure overcomes the disadvantage of poor gas flow, but the interaction region between the light and the target is limited, which affects the sensitivity. The previous VUV lamps only had two electrodes, and the required breakdown voltage was very high, which was not conducive to miniaturization and portability. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies of the prior art, design a toroidal cylindrical structure and combine a reflective film to significantly improve the light utilization efficiency; by designing a plurality of discharge electrodes with different distances, reducing the voltage required for discharge, and adjusting the size of the light generation region by adjusting the voltage on the discharge electrodes, so as to achieve portability and miniaturization, while improving the sensitivity and resolution.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A channel-type VUV ionization source with an adjustable ionization region

[0006] It includes a hollow circular inner cylinder that is open at both ends and transmits vacuum ultraviolet light. An outer insulating cylinder that is open at both ends and hollow is sleeved outside the inner cylinder. There is a gap between the outer wall surface of the inner cylinder and the inner wall surface of the insulating outer cylinder, forming an annular cavity that is open at both ends. Circular sealing end caps are respectively provided at the two open ends of the annular cavity. The circular sealing end caps seal the two open ends of the annular cavity, making the annular cavity form a sealed annular cylindrical discharge cavity. A discharge gas is filled in the discharge cavity;

[0007] More than 3 annular discharge electrodes are coaxially sleeved outside the outer cylinder in sequence, and the more than 3 annular discharge electrodes are respectively connected to an external power source.

[0008] For the ionization source described above, the discharge gas is one or more of helium, neon, argon, krypton, xenon, and nitrogen, and the air pressure range in the discharge cavity is from 1 Pa to 5000 Pa.

[0009] For the ionization source described above, a reflective coating is applied to the inner wall of the outer cylinder or a reflective film is provided; the inner cylinder is made of a material that transmits ultraviolet light, preferably magnesium fluoride glass.

[0010] For the ionization source described above, the circular end caps are hermetically connected to the end faces of the two open ends of the inner cylinder and the insulating outer cylinder respectively, sealing the two open ends of the annular cavity; in order to improve the light utilization efficiency, the axial length of the discharge cavity is greater than the radial thickness, and the axial length is not less than 5 mm.

[0011] For the ionization source described above, an insulating layer is wrapped on the outer wall surface of the outer cylinder; the discharge electrodes are located between the outer cylinder and the insulating layer to prevent discharge outside the cylindrical discharge cavity.

[0012] For the ionization source described above, two adjacent discharge electrodes form a discharge electrode pair, and the distance between the discharge electrode pairs increases sequentially from the left open end to the right open end of the annular cavity; a trigger ionization region is formed between the two closest discharge electrodes; the voltages applied to the 3 discharge electrodes can be switched on and off, and the length of the axial discharge region of the VUV ionization source can be regulated by switching on and off the voltages on the 3 discharge electrodes.

[0013] For the ionization source described above, a DC voltage is applied to the electrodes. From left to right, the voltage between the first and second electrodes is the smallest, and the voltages of the subsequent electrodes increase in sequence. The voltage amplitude between the first and second electrodes is not less than the DC breakdown voltage required for discharge between the first and second electrodes. The voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes. Or, a DC voltage is applied to the electrodes. The voltage between the first and second electrodes is the smallest, and the voltages of the subsequent electrodes increase in sequence. The voltage amplitude between the first and second electrodes is not less than the DC breakdown voltage required for discharge between the first and second electrodes. The voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes. Or, a radio frequency voltage is applied between the first electrode and the second electrode, and a discharge initiation region is formed between the first electrode and the second electrode to trigger the discharge in the region behind the second electrode. The voltage amplitude between the first and second electrodes is not less than the radio frequency breakdown voltage required for discharge between the first and second electrodes. The voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes.

[0014] Application of the ionization source in a mass spectrometer or an ion mobility spectrometer.

[0015] For the application described above, it is characterized in that: the ionization source is used in combination with a mass spectrometer or an ion mobility spectrometer, which can reduce the discharge voltage, improve the photon utilization rate, and improve the sensitivity.

[0016] The advantages of the present invention are as follows: the present invention provides a channel-type VUV ionization source with an adjustable ionization region for an ion mobility spectrometer. Through the channel-type structure design and the combination of a reflective film, the light utilization efficiency is improved. By designing a plurality of discharge electrodes with different distances, the voltage required for discharge is reduced, and the size of the light generation region is adjusted by adjusting the voltage on the discharge electrodes, thereby achieving portability and miniaturization, while improving the sensitivity and resolution. Description of the Drawings

[0017] The present invention will be further described in detail below with reference to the drawings and embodiments:

[0018] Figure 1 It is a schematic structural diagram of a channel-type VUV ionization source with an adjustable ionization region. A hollow circular inner cylinder (1) that transmits vacuum ultraviolet light, an insulating outer cylinder (2), a reflective coating (3), an annular discharge electrode (4), an insulating layer (5), an ionization channel (6), a circular sealing end cover (7), and a discharge cavity (8).

[0019] Figure 2 It is a schematic structural diagram of the combination of the ionization source and an ion mobility spectrometer.

[0020] Figure 3 It is an ion mobility spectrum of the chemical warfare agent simulant DMMP by a channel-type VUV ionization source with an adjustable ionization region. Detailed implementation mode

[0021] A channel-type VUV ionization source with adjustable ionization region

[0022] It includes a hollow circular inner cylinder that transmits vacuum ultraviolet light with two open ends. An outer insulating cylinder with two open ends and a hollow circular shape is sleeved outside the inner cylinder. There is a gap between the outer wall surface of the inner cylinder and the inner wall surface of the insulating outer cylinder, forming an annular cavity with two open ends. Circular sealing end caps are respectively arranged at the two open ends of the annular cavity, and the circular sealing end caps seal the two open ends of the annular cavity, making the annular cavity form a closed annular cylindrical discharge cavity; the discharge gas krypton is filled in the discharge cavity, and the air pressure is 1 Torr; the outer diameter of the hollow circular inner cylinder that transmits vacuum ultraviolet light with two open ends is 15 mm, and the inner diameter is 5 mm.

[0023] More than 3 annular discharge electrodes are coaxially sleeved outside the outer cylinder in sequence, and the more than 3 annular discharge electrodes are respectively connected to an external power supply; the inner diameter of the three annular electrodes is 15.2 mm; the outer diameter is 25 mm.

[0024] A reflective coating is applied to the inner wall of the outer cylinder or a reflective film is provided; the inner cylinder is made of a material that transmits ultraviolet light, preferably magnesium fluoride glass. The thickness of the reflective film is 100 um.

[0025] For the ionization source described above, the circular end caps are hermetically connected to the end faces of the two open ends of the inner cylinder and the insulating outer cylinder respectively, sealing the two open ends of the annular cavity; the axial length of the discharge cavity is 2 cm.

[0026] An insulating layer is wrapped on the outer wall surface of the outer cylinder; the discharge electrode is located between the outer cylinder and the insulating layer to prevent discharge outside the cylindrical discharge cavity. The insulating layer is made of a tetrafluoro material with a thickness of 1 mm.

[0027] Two adjacent discharge electrodes form a discharge electrode pair, and the distance between the discharge electrode pairs increases sequentially from the left open end to the right open end of the annular cavity; the trigger ionization region is formed between the two closest discharge electrodes; the voltages applied to the three discharge electrodes can be turned on and off, and the length of the axial discharge region of the VUV ionization source can be regulated by turning on and off the voltages applied to the three discharge electrodes.

[0028] For the described ionization source, a DC voltage is applied to the electrodes. From left to right, the voltage between the first and second electrodes is the smallest, and the subsequent voltages increase in sequence; the voltage amplitude between the first and second electrodes is not less than the DC breakdown voltage required for discharge between the first and second electrodes; the voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes; or, a DC voltage is applied to the electrodes, the voltage between the first and second electrodes is the smallest, and the subsequent voltages increase in sequence; the voltage amplitude between the first and second electrodes is not less than the DC breakdown voltage required for discharge between the first and second electrodes; the voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes; or, a radio frequency voltage is applied between the first electrode and the second electrode, a discharge initiation region is formed between the first electrode and the second electrode to trigger the discharge in the region behind the second electrode; the voltage amplitude between the first and second electrodes is not less than the radio frequency breakdown voltage required for discharge between the first and second electrodes; the voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes.

[0029] The present invention utilizes a channel-type VUV ionization source with adjustable ionization region to efficiently ionize the sample. The discharge cavity 8 is filled with krypton gas at a pressure of 1 torr, the diameter of the ionization channel 6 is 5 mm, the distance between the discharge electrode 4 and the adjacent discharge electrode is 5 mm, and the voltage difference is 2000 V. For the specific device, see Figure 1 . The sample to be measured enters the ionization channel 6 on the side close to the discharge electrode 4 of the channel-type VUV ionization source with adjustable ionization region under the action of the carrier gas and is ionized to form reaction ions or sample ions.

[0030] The above-described ionization source is combined with an ion mobility spectrometer and used as the ionization source of the ion mobility spectrometer. Its structure is as Figure 2 shown. This instrument mainly includes the following parts: a hollow circular inner cylinder 1 that transmits vacuum ultraviolet light, an insulating outer cylinder 2, a reflective coating 3, a ring-shaped discharge electrode 4, an insulating layer 5, an ionization channel 6, a circular ring-shaped sealed end cap 7, a discharge cavity 8, an ionization reaction region 10, an ion gate 12, a migration region 13, and a Faraday disk 14. The process of detecting the sample is as follows: sample ions are generated in the ionization region between the ion extraction electrodes 8 and 9, and the obtained sample ions enter the migration region 13 through the ion gate 12 opened by a pulse, are separated according to their different mobilities in the migration region 14, and are finally detected at the Faraday disk 17.

[0031] Figure 3 The migration spectrum of the chemical warfare agent simulant DMMP by the channel-type VUV ionization source with adjustable ionization region is given.

Claims

1. A channel-type VUV ionization source with adjustable ionization region, characterized in that: It includes a hollow circular inner cylinder (1) that transmits vacuum ultraviolet light with two open ends. An outer hollow circular insulating outer cylinder (2) with two open ends is sleeved outside the inner cylinder (1). There is a gap between the outer wall surface of the inner cylinder (1) and the inner wall surface of the insulating outer cylinder (2) to form an annular cavity with two open ends. Circular sealing end caps (7) are respectively provided at the two open ends of the annular cavity. The circular sealing end caps (7) seal the two open ends of the annular cavity, making the annular cavity form a sealed annular cylindrical discharge cavity (8); a discharge gas is filled in the discharge cavity (8); Outside the outer cylinder (2), more than 3 annular discharge electrodes (4) are coaxially sleeved in sequence. The more than 3 annular discharge electrodes (4) are respectively connected to an external power supply; adjacent two discharge electrodes form a discharge electrode pair, and the distance between the discharge electrode pairs increases sequentially from the left open end to the right open end of the annular cavity; the trigger ionization region is formed between the two closest discharge electrodes; the voltages applied to the 3 discharge electrodes (4) can be turned on and off, and the length of the axial discharge region of the VUV ionization source can be adjusted by turning on and off the voltages on the 3 discharge electrodes.

2. The ionization source according to claim 1, characterized in that: The discharge gas is one or more of helium, neon, argon, krypton, xenon, and nitrogen, and the air pressure range in the discharge cavity (8) is from 1 Pa to 5000 Pa.

3. The ionization source according to claim 1, characterized in that: A reflective coating (3) is coated on the inner wall of the outer cylinder (2) or a reflective film is provided; the inner cylinder is made of a material that transmits ultraviolet light, and the inner cylinder is magnesium fluoride glass.

4. The ionization source according to claim 1, characterized in that: The circular end caps (7) are hermetically connected to the end faces of the two open ends of the inner cylinder (1) and the insulating outer cylinder (2) respectively to seal the two open ends of the annular cavity; in order to improve the light utilization efficiency, the axial length of the discharge cavity (8) is greater than the radial thickness, and the axial length is not less than 5 mm.

5. The ionization source according to claim 1, wherein: An insulating layer (5) is wrapped on the outer wall surface of the outer cylinder (2); the discharge electrode (4) is located between the outer cylinder (2) and the insulating layer (5) to prevent discharge outside the cylindrical discharge cavity (8).

6. The ionization source according to claim 1, characterized in that: The voltage applied to the electrode is a DC voltage. From left to right, the voltage between the first and second electrodes is the smallest, and the subsequent ones increase in sequence; the voltage amplitude between the first and second electrodes is not less than the DC breakdown voltage required for discharge between the first and second electrodes; the voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes; Or, a radio frequency voltage is applied between the first electrode and the second electrode, and a discharge initiation region is formed between the first electrode and the second electrode to trigger the discharge in the region after the second electrode; the voltage amplitude between the first and second electrodes is not less than the radio frequency breakdown voltage required for discharge between the first and second electrodes; The voltage for discharge between the second and third electrodes is not less than the sustaining voltage required for discharge between the second and third electrodes.

7. Use of the ionization source according to any one of claims 1-6 in mass spectrometry or ion mobility spectrometry, characterized in that: This ionization source is used in combination with a mass spectrometer or an ion mobility spectrometer.

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