Composite ion source ion transfer tube

Abstract

The application discloses a composite ion source ion transfer tube. The ion transfer tube is provided with a photoionization source and a low-pressure planar self-sustained discharge ion source, and the working pressure of the inner chamber is reduced to about 0.3 bar. On the one hand, reducing the working pressure of the inner chamber of the ion transfer tube can effectively inhibit the influence of water vapor light absorption, chemical competitive ionization and other factors on the single-photon ionization process of the target sample, and promote the generation of sample ion M + On the other hand, the low-pressure planar self-sustained discharge can cover the entire radial section of the inner chamber of the ion transfer tube, and the generated hydrated hydrogen positive ion (H2O) n ·H + can further react with sample molecules that are not ionized by ultraviolet light to generate protonated sample ions M·H + , which can not only improve the ionization efficiency of the sample and realize sensitive detection of the target sample, but also provide a new sample characteristic ion peak and realize accurate identification of the target sample.

Description

TECHNICAL FIELD

[0001] The present application relates to the core component of ion mobility spectrometer, ion mobility tube, in particular to an ion mobility tube working at low pressure (~0.3 bar) and equipped with photoionization source and low pressure planar self-sustained discharge ionization source. BACKGROUND

[0002] Atmospheric pressure photoionization is the most commonly used ionization technique in ion mobility spectrometry, which is widely used in the detection of volatile organic pollutants, explosives, drugs, chemical toxicants, etc. The early photoionization technology generally uses laser as the light source, which was first introduced into the field of ion mobility spectrometry by Lubman et al. in 1982 (Anal. Chem. 1982, 54: 1546). With the advent of miniaturized commercial vacuum ultraviolet lamps (VUV lamps), Hill and Eiceman et al. have successively used Krypton VUV lamps and Hydrogen VUV lamps as photoionization sources for ion mobility spectrometry (Anal. Chem. 1983, 55: 1761; Anal. Chem. 1986, 58: 2142). In order to improve the detection sensitivity and target range of photoionization ion mobility spectrometry, Spangler disclosed a photoionization ion mobility spectrometry technology with an axial fixed structure in 1992, using Krypton VUV lamp as photoionization source (US5338931). Hans-Rudiger et al. disclosed a high-sensitivity photoionization ion mobility spectrometry technology based on Dopant doping in 1997 (US5968837), which realized the detection of positive and negative polarity target substances by photoionization ion mobility spectrometry. Li Haiyang et al. disclosed an array photoionization ion mobility tube technology in 2012 to enhance the detection sensitivity in negative ion mode (CN103871828).

[0003] Currently, ion mobility spectrometry instruments generally work at atmospheric pressure and use purified air as the working support gas. On the one hand, O2 and H2O molecules contained in air can absorb a large amount of vacuum ultraviolet light, resulting in an effective transmission distance of ultraviolet light in the ionization region of ion mobility spectrometry of only about 5 mm (Anal. Chem. 2006, 78, 4553), and a large number of sample molecules cannot be ionized due to the lack of contact with ultraviolet light. On the other hand, under atmospheric pressure conditions, complex matrixes present in the sample can cause intense chemical competition ionization with target sample molecules, resulting in further loss of target sample ions, which all cause the insufficient sensitivity of photoionization ion mobility spectrometry in detecting ultra-trace target substances. How to solve the above problems has become an important direction for the development of photoionization ion mobility spectrometry technology. SUMMARY

[0004] The application discloses a composite ion source ion migration tube. The ion migration tube is provided with a photoionization source and a low-pressure planar self-sustained discharge ion source, and the working pressure of the inner chamber is reduced to about 0.3 bar. On one hand, the working pressure of the inner chamber of the ion migration tube is reduced, the influence of water vapor light absorption, chemical competitive ionization and other factors on the single-photon ionization process of the target sample is effectively inhibited, and the generation of sample ion M + + is promoted; on the other hand, the low-pressure planar self-sustained discharge can cover the entire radial section of the inner chamber of the ion migration tube, and the generated hydronium ion (H2O) n ·H + + can further react with sample molecules which are not ionized by ultraviolet light to generate protonated sample ions M·H + +, which can improve the ionization efficiency of the sample, realize sensitive detection of the target sample, and provide a brand-new sample characteristic ion peak to realize accurate identification of the target sample.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0006] A composite ion source ion migration tube, the ion migration tube is a hollow cylindrical cavity composed of ring-shaped electrodes and ring-shaped insulators which are alternately coaxially stacked from left to right, a left end plate electrode is arranged at the left end of the cavity, a right end plate electrode is arranged at the right end of the cavity, and the left and right end plate electrodes are respectively sealed and connected with the circumference of the cavity through the ring-shaped insulators; an ion gate is arranged between the left and right end plate electrodes in the cavity, so that the cavity is divided into left and right two areas, and each area includes two or more ring-shaped electrodes, wherein the ionization zone is formed between the left end plate electrode and the ion gate, and the migration zone is formed between the ion gate and the right end plate electrode; an ion source is arranged on the left end plate electrode, and an ion receiving electrode is arranged on the right end plate electrode;

[0007] A sample gas inlet and a gas outlet are arranged on the left end plate electrode, and a drift gas inlet is arranged on the right end plate electrode; the sample gas inlet, the drift gas inlet and the gas outlet are respectively communicated with the inner chamber of the ion migration tube, one-way drift gas enters the inside of the migration zone through the drift gas inlet, flows into the ionization zone through the ion gate, mixes with the sample gas entering the ionization zone through the sample gas inlet, and then flows out of the ion migration tube through the gas outlet; the gas outlet is connected with the gas suction port of a vacuum pump, and the gas pressure in the inner chamber of the ion migration tube is controlled to change between 1 bar and 0.1 bar;

[0008] The ion source is any light source capable of emitting ultraviolet light of any wavelength of 80-150 nm; the ultraviolet light emitted by the light source outlet enters the inner cavity of the ionization zone along the axis of the ion migration tube, is absorbed by the sample molecules entering the ionization zone through the sample gas inlet, and generates sample molecule ions M + + with positive charges;

[0009] The first annular electrode and the second annular electrode adjacent to the ion source in the ionization zone constitute a discharge electrode pair, the middle through holes of the first annular electrode and the second annular electrode are respectively provided with circular sheet metal meshes with a mesh number of 20-80 meshes, the circular planes of the two metal meshes are perpendicular to the axis of the ion mobility tube, and the distance between the circular planes of the two metal meshes is 1-3 mm;

[0010] When the gas pressure in the inner chamber of the ion mobility tube is reduced to 0.1-0.3 bar, the potential difference between the first annular electrode and the second annular electrode is adjusted to be greater than 1000 V, the low-pressure planar self-sustaining discharge between the discharge electrode pair covers the entire radial section of the inner chamber of the ion mobility tube, and the second ion source of the ion mobility tube is formed, the discharge generated hydrated hydrogen positive ions (H2O) n ·H + further react with sample molecules not ionized by ultraviolet light to generate protonated sample ions M·H + , on the one hand, the sample ionization efficiency is improved, the sensitive detection of the target sample is realized, and on the other hand, a new sample characteristic ion peak is provided, and the accurate identification of the target sample is realized;

[0011] The ion gate is one of a Bradbury-Neilsen type ion gate or a Tyndall-Powell type ion gate.

[0012] The floating gas is compressed air filtered through a molecular sieve and activated carbon.

[0013] The application reduces the working gas pressure in the inner chamber of the ion mobility tube, and simultaneously sets a photoionization source and a low-pressure planar self-sustaining discharge ionization source, on the one hand, the influence of water vapor light absorption, chemical competitive ionization and other factors on the single-photon ionization process of the target sample is solved, the working gas pressure in the inner chamber of the ion mobility tube is reduced, the influence of oxygen and trace water vapor light absorption, chemical competitive ionization and other factors on the single-photon ionization process of the target sample is effectively inhibited, and the generation of sample ions M + is promoted; on the other hand, the low-pressure planar self-sustaining discharge can cover the entire radial section of the inner chamber of the ion mobility tube, the hydrated hydrogen positive ions (H2O) n ·H + generated by the low-pressure planar self-sustaining discharge can further react with sample molecules not ionized by ultraviolet light to generate protonated sample ions M·H + , which can improve the sample ionization efficiency, realize the sensitive detection of the target sample, and provide a new sample characteristic ion peak for the accurate identification of the target sample; the low-pressure planar discharge has a wide coverage, can fully react with sample molecules not ionized by ultraviolet light, improve the sample ionization efficiency, and additionally provide a sample characteristic ion peak.

[0014] The ion migration tube disclosed by the application combines low-pressure planar discharge with photoionization ion mobility spectrum, can solve the influence of water vapor light absorption, chemical competitive ionization and other factors on the single-photon ionization process of the target sample, can further improve the sample ionization efficiency by using the wide coverage advantage of low-pressure planar discharge, and provides a brand-new sample characteristic ion peak. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The structure diagram of the composite ion source ion migration tube disclosed by the application is shown in the figure. In the figure, 1 is an ultraviolet ionization source, 2 is an ionization zone, 3 is an ion gate, 4 is a migration zone, 5 is an ion receiving electrode, 6 is a ring electrode, 6-1 is a first ring electrode, 6-2 is a second ring electrode, 7 is a ring insulator, 8 is a sample gas inlet, 9 is a drift gas inlet, and 10 is an outlet.

[0016] Figure 2 The spectrum obtained by the composite ion source ion migration tube disclosed by the application under different working modes is shown in the figure. (1) Ion mobility spectrum of 200 ppb anisole when single photoionization works, (2) ion mobility spectrum of 200 ppb anisole when photoionization and planar self-sustaining discharge work simultaneously. DETAILED DESCRIPTION

[0017] Example 1

[0018] The composite ion source ion migration tube disclosed by the application is shown in the figure. Figure 1

[0019] The ion migration tube is a hollow cylindrical cavity composed of the circular ring electrode 6 and the circular ring insulator 7 alternately and coaxially stacked from left to right, a left end plate electrode is arranged at the left end of the cavity, a right end plate electrode is arranged at the right end of the cavity, the left and right end plate electrodes are respectively sealed and connected with the left and right openings of the cylindrical cavity through the circular ring insulator 7, thereby forming a closed cylindrical chamber; an ion gate 3 is arranged between the left and right end plate electrodes in the cavity, thereby dividing the cavity into two left and right regions, and each region includes two or more ring electrodes 6, wherein the left end plate electrode and the ion gate 3 form an ionization zone 2, and the ion gate 3 and the right end plate electrode form a migration zone 4; an ion source 1 is arranged on the left end plate electrode, and an ion receiving electrode 5 is arranged on the right end plate electrode in the cavity.

[0020] ​The first ion source of the ion migration tube is an ultraviolet photoionization source 1 composed of a 10.6 eV VUV Kr lamp, which is fixed on the left end plate electrode; the ionization zone 2 and the migration zone 4 are both composed of coaxial alternately stacked ring electrodes with an axial length of 3.5 mm, an outer diameter of 30 mm, and an inner diameter of 20 mm, and ring insulators with an axial length of 1.5 mm, an outer diameter of 30 mm, and an inner diameter of 20 mm; the axial length of the ionization zone 2 is 36.5 mm, and the axial length of the migration zone 4 is 35 mm; the ion gate 3 is a Bradbury-Nielsen ion gate with a wire diameter of 0.1 mm and a wire spacing of 1 mm; the ion receiving electrode 5 is a Faraday cup with a diameter of 6 mm, which is fixed and sealed by insulation on the right end plate electrode with an outer diameter of 30 mm; a circular metal mesh with a thickness of 0.05 mm and an outer diameter of 20 mm is arranged in the through hole of the first ring electrode 6-1 and the second ring electrode 6-2, and the plane spacing of the metal mesh is 1.5 mm;

[0021] A sample gas inlet 8 and a gas outlet 10 are arranged on the left end plate electrode, and a drift gas inlet 9 is arranged on the left end plate electrode; one way of 500 mL / min of drift gas enters the ion migration tube through the drift gas inlet 9, flows into the ionization zone 2 through the ion gate 3, mixes with one way of 100 mL / min of sample gas entering the ionization zone 2 through the sample gas inlet 8, and then flows out of the ion migration tube through the gas outlet 10; the drift gas is clean air filtered by activated carbon and 13X molecular sieve in sequence, and the sample gas is clean air containing a specific concentration of target analyte; the gas outlet 10 is connected to the suction port of the vacuum pump, and the gas pressure in the ion migration tube chamber can be reduced from atmospheric pressure to 0.1 bar by controlling the suction speed of the suction pump; the drift gas is purified air filtered by silica gel, molecular sieve, and activated carbon, which contains about 10 ppb of trace water vapor, and the sample gas is purified air carrying the target molecules to be measured.

[0022] As shown in Figure 2 , the gas pressure in the ion migration tube chamber is controlled to be about 0.3 bar, and when the potential difference between the first ring electrode 6-1 and the second ring electrode 6-2 is adjusted to 1200 V, low-pressure planar self-sustained discharge can occur, which constitutes the second ion source of the ion migration tube.

[0023] As shown in Figure 2 , the gas pressure in the ion migration tube chamber is controlled to be about 0.3 bar, and when the potential difference between the first ring electrode 6-1 and the second ring electrode 6-2 is adjusted to 1200 V, low-pressure planar self-sustained discharge can occur, which constitutes the second ion source of the ion migration tube. + When the ion migration tube works in the combined ion source mode, that is, the ultraviolet light ion source 1 and the low-pressure planar self-sustained discharge ion source composed of the first ring electrode 6-1 and the second ring electrode 6-2 work simultaneously, the ion mobility spectrum formed by the sample gas containing 200 ppb of anisole is shown in (2), and a M·H +Ion peaks and M + Ion peaks. By comparing the spectra (1) and (2), it can be concluded that the complex ionization source mode can provide higher ion signal intensity and more ion spectral peak information.

Claims

1. A composite ion source ion transfer tube, the ion transfer tube is a hollow cylindrical cavity composed of left-to-right alternating coaxial stacking of circular ring electrodes (6) and circular ring insulators (7), a left end plate electrode is arranged at the left end of the cavity, a right end plate electrode is arranged at the right end of the cavity, the left and right end plate electrodes are respectively sealed and connected with the left and right two open ends of the cylindrical cavity through the circular ring insulator (7), forming a closed cylindrical cavity; an ion gate (3) is arranged between the left and right end plate electrodes inside the cavity, dividing the cavity into two regions, and each region includes two or more ring electrodes (6), wherein, The ionization zone (2) is formed between the left end plate electrode and the ion gate (3), and the migration zone (4) is formed between the ion gate (3) and the right end plate electrode; the ion source (1) is arranged on the left end plate electrode, and the ion receiving electrode (5) is arranged on the right end plate electrode in the cavity, characterized in that: The sample gas inlet (8) and the gas outlet (10) are arranged on the left end plate electrode, and the drift gas inlet (9) is arranged on the right end plate electrode; the sample gas inlet (8), the drift gas inlet (9) and the gas outlet (10) are respectively communicated with the inner chamber of the ion migration tube; one way of drift gas enters the inside of the migration zone (4) through the drift gas inlet (9), flows into the ionization zone (2) through the ion gate (3), and then flows out of the ion migration tube through the gas outlet (10) after mixing with the sample gas entering the ionization zone (2) through the sample gas inlet (8); the gas outlet (10) is connected with the air outlet of the vacuum pump, and the gas pressure in the inner chamber of the ion migration tube is controlled to change between 1 bar and 0.1 bar; The ion source (1) is any light source capable of emitting ultraviolet light of any wavelength of 80-150 nm, and the ultraviolet light emitted by the light source outlet enters the inner cavity of the ionization zone (2) along the axis of the ion migration tube, is absorbed by the sample molecules entering the ionization zone (2) through the sample gas inlet (8), and undergoes single-photon ionization to generate positively charged sample molecular ions M + ; The first annular electrode (6-1) adjacent to the right side of the ion source (1) in the ionization zone (2) and the second annular electrode (6-2) close to the right side of the first annular electrode (6-1) constitute a discharge pair of electrodes; the mesh number of the circular sheet metal grid arranged at the middle through hole of the first annular electrode (6-1) and the second annular electrode (6-2) is 20-80 meshes; the circular planes of the two metal grid are perpendicular to the axis of the ion migration tube, and the distance between the circular planes of the two metal grid is 1-3 mm; When the gas pressure in the inner chamber of the ion migration tube is reduced to 0.1-0.3 bar, the low-pressure planar self-sustaining discharge can occur by adjusting the potential difference between the first annular electrode (6-1) and the second annular electrode (6-2) to be greater than 1000 V, thereby forming the second ion source of the ion migration tube.

2. The ion migration tube according to claim 1, characterized in that: The low-pressure planar self-sustained discharge formed between the first ring electrode (6-1) and the second ring electrode (6-2) can cover the entire radial cross-section of the inner chamber of the ion mobility tube, and the hydrogen hydrate ions (H2O) n ·H + further react with sample molecules that are not ionized by the ultraviolet light to generate protonated sample ions M·H + .

3. The ion migration tube according to claim 1, characterized in that: The ion gate (3) is one of Bradbury-Neilsen type ion gate or Tyndall-Powell type ion gate; The drift gas is compressed air filtered by molecular sieve and / or activated carbon.

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