A radio frequency enhanced photochemical ionization source

Abstract

The application relates to a radio frequency enhanced photochemical ionization source, which mainly comprises a reagent gas inlet pipe, a sample gas inlet pipe, a gas mixing area, a UVU lamp, a ring-shaped repelling electrode, a ring-shaped focusing electrode, a radio frequency hexapole and a perforated electrode for realizing vacuum difference. The VUV lamp is used as an ionization source, reagent molecules are flexibly selected according to different detection samples, and the universality is good; the collision frequency of reagent ions and sample molecules is increased at low pressure through the radio frequency hexapole, so that the probability of molecular ion reaction is increased, the transmission efficiency of ions is increased through collision focusing, the enhancement of the photochemical ionization source is realized, and the detection sensitivity of the instrument is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a radio frequency enhanced photochemical ionization source. The VUV lamp is used as the ionization source, and the reagent molecules are flexibly selected according to different detection samples, and the universality is good. The collision frequency of the reagent ions and the sample molecules is increased at low pressure by the radio frequency hexapole, so as to increase the probability of the molecular ion reaction. At the same time, the transmission efficiency of the ions is improved by the collision focusing, the enhancement of the photochemical ionization source is realized, and the detection sensitivity of the instrument is significantly improved. BACKGROUND

[0002] Photoionization is particularly suitable for the detection of volatile and semi-volatile organic matter due to its threshold ionization characteristics and simple spectral background. In the case of determined light flux, optical path and sample molecules, the sensitivity of photoionization is limited by high vacuum photoionization. Increasing the pressure in the ionization zone is one of the most effective measures to improve the sensitivity of photoionization. In recent years, low-pressure photoionization mass spectrometry has made great progress.

[0003] In 2015, the research group of Professor Shu Jinyin of the Ecological Environment Research Center of the Chinese Academy of Sciences proposed a low-pressure photoionization mass spectrometer based on a VUV lamp. The VUV lamp is a self-made radio frequency krypton lamp, and the light flux is about 5x10 14 Photons / s (123.9 nm). The ionization zone pressure is 500-1000 Pa, and the detection limit of benzene, toluene and ethylbenzene reaches the sub-pptv level within 10 s of collection time. The ionization source is used for ultra-high sensitivity detection of different cancer VOCs markers and explosives in exhaled breath. However, photoionization is powerless for substances with ionization energy higher than the energy of VUV photons.

[0004] In order to broaden the application range of photoionization and improve the sensitivity of photoionization, a radio frequency enhanced photochemical ionization source is proposed. The ions generated by the easily ionized reagent molecules are used as reactants to produce the sample ions by molecular ion reaction. The radio frequency hexapole can improve the collision probability of the reagent ions and the sample molecules, thereby improving the probability of the molecular ion reaction. At the same time, the radio frequency hexapole improves the ion transmission efficiency by collision focusing, thereby significantly improving the detection sensitivity of the instrument. SUMMARY

[0005] The present application relates to a radio frequency enhanced photochemical ionization source. The VUV lamp is used as the ionization source, and the reagent molecules are flexibly selected according to different detection samples, and the universality is good. The collision frequency of the reagent ions and the sample molecules is increased at low pressure by the radio frequency hexapole, so as to increase the probability of the molecular ion reaction. At the same time, the transmission efficiency of the ions is improved by the collision focusing, the enhancement of the photochemical ionization source is realized, and the detection sensitivity of the instrument is significantly improved.

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

[0007] A radio frequency enhanced photochemical ionization source comprises a reagent gas inlet tube (1), a sample gas inlet tube (2), a gas mixing zone guide tube (3), a ring-shaped repelling electrode (4), a ring-shaped focusing electrode (5), a VUV lamp (6), a radio frequency hexapole (7), a perforated electrode (8), a vacuum pump (9), an ionization zone cavity (10) and a mass analyzer (11).

[0008] The ionization zone cavity (10) is a hollow sealed cavity, and the ring-shaped repelling electrode (4), the ring-shaped focusing electrode (5), the radio frequency hexapole (7) and the perforated electrode (8) are sequentially arranged in the ionization zone cavity (10) from left to right.

[0009] The outlet ends of the reagent gas inlet tube (1) and the sample gas inlet tube (2) respectively extend into the ionization zone cavity (10) through the wall surface of the ionization zone cavity (10); the outlet end of the gas mixing zone guide tube (3) extends into the region between the ring-shaped repelling electrode (4) and the ring-shaped focusing electrode (5) through the central through hole of the ring-shaped repelling electrode (4); the outlet ends of the reagent gas inlet tube and the sample gas inlet tube respectively face the inlet of the gas mixing zone guide tube, and the included angles between the axes of the outlet ends of the reagent gas inlet tube and the sample gas inlet tube and the axis of the inlet of the gas mixing zone guide tube are respectively 30°-45°.

[0010] The perforated electrode (8) is a flat plate-shaped electrode with a central through hole, and the central through hole of the ring-shaped repelling electrode (4), the outlet end of the gas mixing zone guide tube (3), the central through hole of the ring-shaped focusing electrode (5), the symmetry axis (ion transmission direction) of the radio frequency hexapole (7) and the central through hole of the perforated electrode (8) are coaxial.

[0011] A through hole A is arranged on the right side wall of the ionization zone cavity (10) close to the perforated electrode (8), the central through hole of the perforated electrode (8) corresponds to the position of the through hole A, the central through hole of the perforated electrode (8) is in communication with the outside of the ionization zone cavity (10) through the through hole A, and the mass analyzer (11) is arranged outside the through hole A.

[0012] A VUV lamp (6) is arranged on the side wall of the ionization zone cavity (10), the light outlet of the VUV lamp (6) faces the inside of the cavity, the emitted light of the VUV lamp is transmitted in the cavity along a direction perpendicular to the axis of the central through hole of the ring-shaped repelling electrode (4), irradiates the region between the ring-shaped repelling electrode (4) and the ring-shaped focusing electrode (5), and forms a reagent ion generation zone in the cavity.

[0013] A through hole B is arranged on the side wall of the ionization zone cavity (10), and the through hole B is connected with the inlet of the vacuum pump (9).

[0014] The annular repelling electrode (4) and the reagent ion generating area are respectively located at the left and right sides of the gas mixing area (3) outlet, and the reagent ion generating area and the radio frequency hexapole (7) are respectively located at the left and right sides of the annular focusing electrode (5).

[0015] The outlet end of the reagent gas sampling tube and the outlet end of the sample gas sampling tube are respectively connected with the gas mixing area conduit inlet end.

[0016] The ionization area cavity gas pressure is 100-500 Pa.

[0017] The reagent gas sampling tube (1) and the sample gas sampling tube (2) are one of metal capillary, peek capillary and quartz capillary, the length is 0.1 m-1 m, and the inner diameter is 0.25 mm-1 mm; the stainless steel conduit length of the gas mixing area is 10 mm-30 mm, and the inner diameter is 0.5 mm-1 mm.

[0018] The inner diameter of the middle through hole of the annular repelling electrode (4) is 0.5-5 mm, the inner diameter of the middle through hole of the annular focusing electrode (5) is 5-10 mm, and the diameter of the middle through hole of the aperture electrode (8) is 0.3-0.6 mm.

[0019] Different voltages V1, V2 and V3 are loaded on the annular repelling electrode (4), the annular focusing electrode (5) and the aperture electrode (8) in the order from high to low, and the voltage difference is 10-50 V;

[0020] The frequency of the radio frequency voltage applied on the radio frequency hexapole is 1-2.5 MHz, the peak V p-p is 100-340 V adjustable, the radio frequency phase difference of adjacent rods is 180°; a direct current voltage V4 is superimposed on the applied radio frequency voltage, and the V4 voltage size is between V2 and V3, so as to ensure the smooth extraction of ions

[0021] The middle through hole of the aperture electrode (8) corresponds to the ion inlet of the mass analyzer (11), and the mass analyzer is an ion trap mass analyzer, a time of flight mass analyzer or a quadrupole mass analyzer.

[0022] The advantages of the present application are: the present application has the outstanding advantages that the sample which cannot be photoionized by introducing reagent molecules photochemical ionization detection is introduced, and the application range of photoionization is widened. The collision probability of reagent ions and sample molecules is improved by introducing a radio frequency hexapole, so as to improve the probability of molecular ion reaction, and the radio frequency hexapole realizes focusing of ions through collision focusing, improves the transmission efficiency of ions, and significantly improves the detection sensitivity of the instrument. BRIEF DESCRIPTION OF DRAWINGS

[0023] The present application will be further described in detail in combination with the drawings and examples:

[0024] Figure 1 A schematic diagram of the structure of a radio frequency enhanced photochemical ionization source involved in the present application, wherein 1 is a reagent gas inlet tube, 2 is a sample gas inlet tube, 3 is a gas mixing area, 4 is a ring-shaped repelling electrode, 5 is a ring-shaped focusing electrode, 6 is a VUV lamp, 7 is a radio frequency hexapole, 8 is an open hole electrode, 9 is a vacuum pump, 10 is an ionization area cavity, and 11 is a mass analyzer. DETAILED DESCRIPTION

[0025] Example 1

[0026] In order to make the content of the present application more clear and easy to understand, the content of the present application is described in detail below in combination with specific examples and drawings.

[0027] The ionization area cavity (10) is a hollow sealed cavity, and the ring-shaped repelling electrode (4), the ring-shaped focusing electrode (5), the radio frequency hexapole (7), and the open hole electrode (8) are sequentially arranged in the ionization area cavity (10) from left to right.

[0028] The outlet ends of the reagent gas inlet tube (1) and the sample gas inlet tube (2) respectively pass through the wall surface of the ionization area cavity (10) and extend into the ionization area cavity (10); the outlet end of the gas mixing area guide pipe (3) passes through the central through hole of the ring-shaped repelling electrode (4) and extends into the area between the ring-shaped repelling electrode (4) and the ring-shaped focusing electrode (5); the outlet ends of the reagent gas inlet tube and the sample gas inlet tube respectively face the inlet of the gas mixing area guide pipe, and the included angles between the axes of the outlet ends of the reagent gas inlet tube and the sample gas inlet tube and the axis of the inlet of the gas mixing area guide pipe are respectively 30°-45°.

[0029] The open hole electrode (8) is a flat plate-shaped electrode with a through hole in the middle, the central through hole of the ring-shaped repelling electrode (4), the outlet end of the gas mixing area guide pipe (3), the central through hole of the ring-shaped focusing electrode (5), the symmetry axis (ion transmission direction) of the radio frequency hexapole (7), and the central through hole of the open hole electrode (8) are coaxial.

[0030] A through hole A is arranged on the right side wall surface of the ionization area cavity (10) close to the open hole electrode (8), the central through hole of the open hole electrode (8) corresponds to the position of the through hole A, the central through hole of the open hole electrode (8) communicates with the outside of the ionization area cavity (10) through the through hole A, and a mass analyzer (11) is arranged outside the through hole A of the ionization area cavity (10).

[0031] A VUV lamp (6) is arranged on the side wall surface of the ionization area cavity (10), the light outlet of the VUV lamp (6) faces the inside of the cavity, the emitted light of the VUV lamp is transmitted in the cavity along a direction perpendicular to the axis of the central through hole of the ring-shaped repelling electrode (4), irradiates the area between the ring-shaped repelling electrode (4) and the ring-shaped focusing electrode (5), and forms a reagent ion generation area in the cavity.

[0032] The side wall of the ionization zone cavity (10) is provided with a through hole B connected with the inlet of the vacuum pump (9).

[0033] The annular repelling electrode (4) and the reagent ion generation zone are respectively located on the left and right sides of the outlet of the gas mixing zone (3), and the reagent ion generation zone and the radio frequency hexapole rod (7) are respectively located on the left and right sides of the annular focusing electrode (5).

[0034] The outlet end of the reagent gas sampling tube and the outlet end of the sample gas sampling tube are respectively connected with the inlet end of the gas mixing zone conduit.

[0035] The gas pressure in the ionization zone cavity is 100-500 Pa.

[0036] The reagent gas sampling tube (1) and the sample gas sampling tube (2) are respectively one of a metal capillary tube, a peek capillary tube and a quartz capillary tube, with a length of 0.1 m-1 m and an inner diameter of 0.25 mm-1 mm; the length of the stainless steel conduit of the gas mixing zone is 10 mm-30 mm, and the inner diameter is 0.5 mm-1 mm.

[0037] The inner diameter of the through hole in the middle part of the annular repelling electrode (4) is 0.5-5 mm, the inner diameter of the through hole in the middle part of the annular focusing electrode (5) is 5-10 mm, and the diameter of the through hole in the middle part of the aperture electrode (8) is 0.3-0.6 mm.

[0038] Different voltages V1, V2 and V3 are loaded on the annular repelling electrode (4), the annular focusing electrode (5) and the aperture electrode (8) in the order from high to low, and the voltage difference is 10-50 V.

[0039] The frequency of the radio frequency voltage applied to the radio frequency hexapole rod is 1-2.5 MHz, and the peak value V p-p is adjustable between 100 V and 340 V, and the radio frequency phase difference between adjacent rods is 180°; a direct current voltage V4 is superimposed on the applied radio frequency voltage, and the voltage V4 is between V2 and V3, so as to ensure the smooth extraction of ions

[0040] The middle part of the through hole of the aperture electrode (8) corresponds to the ion inlet of the mass analyzer (11), and the mass analyzer is an ion trap mass analyzer, a time-of-flight mass analyzer or a quadrupole rod mass analyzer.

[0041] In specific implementation, the gas pressure in the ionization zone cavity is 133 Pa, the voltage of the annular repelling electrode V1 is 40 V, the voltage of the annular focusing electrode V2 is 20 V, the voltage of the aperture electrode V3 is 1 V, the frequency of the radio frequency hexapole rod is 2.4 MHz, and the peak-to-peak value V p-pThe direct current voltage is 280V and the direct current voltage is 17V. The reagent molecules and the sample molecules enter the gas mixing area conduit through the reagent gas sampling tube and the sample gas sampling tube respectively, are sprayed out from the gas mixing area conduit outlet together into the reagent ion generation area, a large amount of reagent ions and a small amount of sample ions are generated, the reagent ions enter the radio frequency hexapole under the driving of the axial electric field, and the sample molecules enter the radio frequency hexapole under the driving of the gas flow field. The collision probability of the reagent ions and the sample molecules is improved through the radio frequency hexapole, so that the molecular ion reaction probability is improved, the yield of the sample ions is improved. Meanwhile, the product ions in the radio frequency hexapole collide with the neutral gas to focus and improve the transmission efficiency. The generated reagent ions and sample ions enter the mass analyzer through the extraction electrode under the driving of the annular focusing voltage and the hexapole direct current voltage.

Claims

1. A radio frequency enhanced photochemical ionization source comprising a reagent gas inlet tube (1), a sample gas inlet tube (2), a gas mixing zone guide tube (3), a ring-shaped repeller electrode (4), a ring-shaped focusing electrode (5), a VUV lamp (6), a radio frequency hexapole (7), a skimmer electrode (8), a vacuum pump (9), an ionization zone cavity (10) and a mass analyzer (11), characterized in that: the ionization zone cavity (10) is a hollow closed cavity, and the ring-shaped repeller electrode (4), the ring-shaped focusing electrode (5), the radio frequency hexapole (7) and the skimmer electrode (8) are sequentially arranged in the ionization zone cavity (10) from left to right; the outlet ends of the reagent gas inlet tube (1) and the sample gas inlet tube (2) respectively extend into the ionization zone cavity (10) through the wall surface of the ionization zone cavity (10); the outlet end of the gas mixing zone guide tube (3) extends into the region between the ring-shaped repeller electrode (4) and the ring-shaped focusing electrode (5) through the central through hole of the ring-shaped repeller electrode (4); the outlet ends of the reagent gas inlet tube and the sample gas inlet tube respectively face the inlet of the gas mixing zone guide tube, and the angles between the axes of the outlet ends of the reagent gas inlet tube and the sample gas inlet tube and the axis of the inlet of the gas mixing zone guide tube are both 30°-45°; the skimmer electrode (8) is a flat plate electrode with a through hole in the middle, the central through hole of the ring-shaped repeller electrode (4), the outlet end of the gas mixing zone guide tube (3), the central through hole of the ring-shaped focusing electrode (5), the symmetry axis (ion transmission direction) of the radio frequency hexapole (7) and the central through hole of the skimmer electrode (8) are coaxial; a through hole A is arranged on the right side wall of the ionization zone cavity (10) close to the skimmer electrode (8), the central through hole of the skimmer electrode (8) corresponds to the position of the through hole A, the central through hole of the skimmer electrode (8) communicates with the outside of the ionization zone cavity (10) through the through hole A, and the mass analyzer (11) is arranged outside the through hole A; a VUV lamp (6) is arranged on the side wall of the ionization zone cavity (10), the light outlet of the VUV lamp (6) faces the inside of the cavity, the emitted light of the VUV lamp is transmitted in the cavity along a direction perpendicular to the axis of the central through hole of the ring-shaped repeller electrode (4), irradiates the region between the ring-shaped repeller electrode (4) and the ring-shaped focusing electrode (5), and forms a reagent ion generation zone in the cavity; a through hole B is arranged on the side wall of the ionization zone cavity (10), and the through hole B is connected with the inlet of the vacuum pump (9). The ring-shaped repeller electrode (4) and the reagent ion generation zone are respectively located on the left and right sides of the outlet of the gas mixing zone guide tube (3), and the reagent ion generation zone and the radio frequency hexapole (7) are respectively located on the left and right sides of the ring-shaped focusing electrode (5). The outlet ends of the reagent gas inlet tube and the sample gas inlet tube are respectively attached to the inlet end of the gas mixing zone guide tube. The gas pressure in the ionization zone cavity is 100-500 Pa.

5. The photochemical ionization source according to claim 1, characterized in that: ​ ​ 2. The photochemical ionization source of claim 1, wherein: ​ 3. The photochemical ionization source of claim 1, wherein: ​ 4. The photochemical ionization source of claim 1, wherein: ​ ​ The reagent gas inlet tube (1) and the sample gas inlet tube (2) are one of a metal capillary tube, a peek capillary tube and a quartz capillary tube, with a length of 0.1-1m and an inner diameter of 0.25-1mm; the stainless steel conduit of the gas mixing area has a length of 10-30mm and an inner diameter of 0.5-1mm.

6. The photochemical ionization source according to claim 1, wherein: The inner diameter of the through hole in the middle of the ring-shaped repelling electrode (4) is 0.5-5mm, the inner diameter of the through hole in the middle of the ring-shaped focusing electrode (5) is 5-10mm, and the diameter of the through hole in the middle of the aperture electrode (8) is 0.3-0.6mm.

7. The photochemical ionization source according to claim 1, wherein: Different voltages V1, V2 and V3 are loaded on the ring-shaped repelling electrode (4), the ring-shaped focusing electrode (5) and the aperture electrode (8) in the order from high to low, and the voltage difference is 10-50V; The frequency of the radio frequency voltage applied on the radio frequency hexapole rod is 1-2.5MHz, the peak Vp-p is adjustable in the range of 100-340V, and the phase difference of the radio frequency of adjacent rods is 180°; a direct current voltage V4 is superimposed on the applied radio frequency voltage, and the voltage of V4 is between V2 and V3, so as to ensure the smooth extraction of ions.

8. The photochemical ionization source according to claim 1, wherein: The through hole in the middle of the aperture electrode (8) corresponds to the ion inlet of the mass analyzer (11), and the mass analyzer is an ion trap mass analyzer, a time-of-flight mass analyzer or a quadrupole rod mass analyzer.

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