Discharge ionization source for ion mobility spectrometry and application

Abstract

The invention discloses a discharge ionization source for an ion mobility spectrometry. The discharge ionization source is designed by adopting a low-temperature plasma discharge principle. A radio frequency electrode of the discharge ionization source is a rod-shaped metal electrode arranged in an inner cavity of the single-end-opened quartz glass tube, direct-current electrodes of the discharge ionization source are arranged on the outer wall face of the discharge glass tube body in an array mode at equal intervals, the potential of each direct-current electrode can be independently adjusted, and the direction of a direct-current electric field in the ionization source can be conveniently adjusted and controlled. The migration direction of the ions is further controlled; in addition, a plurality of gas interfaces are arranged on the quartz glass tube, so that the gas flow direction in the quartz glass tube and the components of the discharge gas can be regulated and controlled. Based on the structural design of the array type direct current discharge electrode and the multi-gas interface, the discharge ionization source takes air as discharge gas, can realize positive and negative ion mode switching, reaction reagent ion component switching and sample ionization mode switching, and is simple in structure, convenient to operate and suitable for the ion mobility spectrometer.

Description

Technical Field

[0001] The present invention relates to an ionization source for ion mobility spectrometry. Specifically, it is a low-temperature plasma discharge ionization source with controllable ionization paths and reagent ions. Background Art

[0002] Ion Mobility Spectrometry (IMS) is a mainstream technology for detecting trace target substances such as explosives, drugs, chemical warfare agents, and industrial hazardous chemicals. As an important part of the ion mobility spectrometer, the ion source primarily determines whether the target can be detected and the direct detection sensitivity. Due to its simple structure and ability to provide high-abundance reagent ions, the discharge ionization source is highly favored by IMS technology developers. For example, the dielectric barrier discharge ionization source developed by Professor Jiang Jie of Harbin Institute of Technology (CN103776893), the corona discharge ionization source developed by Professor Ni Kai of Tsinghua University (CN110289203), the multi-needle corona discharge ionization source developed by Zheng Haidong et al. of the First Research Institute of the Ministry of Public Security (CN110189978), and so on.

[0003] Discharge ionization sources usually require expensive inert gases (such as helium, argon, etc.) to obtain single-component reagent ions, making it difficult to meet the requirements of portable on-site applications of ion mobility spectrometers. When air is used as the discharge gas, the discharge ionization source often has problems such as the generation of ozone and nitrogen oxides, resulting in uncontrollable reagent ion components and the complication of the ionization process caused by excited-state neutral particles. Therefore, how to develop a discharge ionization source with controllable reagent ions and ionization process using air as the discharge gas has always been the direction of efforts of IMS technology researchers. Summary of the Invention

[0004] The present invention provides a discharge ionization source based on the principle of low-temperature plasma discharge. By using an array of DC discharge electrodes and a multi-gas interface design, air is used as the discharge gas to achieve functions such as positive and negative ion mode switching, reagent ion component switching, and sample ionization mode switching.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A discharge ionization source for ion mobility spectrometry, comprising a radio frequency discharge needle, a quartz glass tube, and a DC electrode;

[0007] The quartz glass tube is a cylindrical tube body with a sealed left end and an open right end. Along the direction from the right end to the left end of the quartz glass tube, a first annular DC electrode, a second annular DC electrode, ……, an (N - 1)th annular DC electrode, and an Nth annular DC electrode are successively sleeved on the outer wall surface of the quartz glass tube at equal intervals. N is a positive integer greater than or equal to 4. Among them, the first annular DC electrode is close to the right end of the quartz glass tube, and the Nth annular DC electrode is close to the left end of the quartz glass tube;

[0008] The RF discharge needle is a round rod-shaped metal electrode. The left bottom surface inside the tube body of the quartz glass tube is a hemispherical surface protruding to the left. The center of the sphere of the hemispherical surface is located on the axis of the tube body. A through hole A is opened along the axis direction on the hemispherical bottom surface. One end of the RF discharge needle passes through the through hole A and extends into the tube body, and the other end is outside the tube body. The outer wall surface of the RF discharge needle is hermetically connected to the inner wall surface of the through hole A. The RF discharge needle is coaxial with the quartz glass tube. The end plane of the end of the RF discharge needle inside the tube body extends along the axis of the quartz glass tube to the midpoint of the connection line between the left end face of the third annular DC electrode and the right end face of the fourth annular DC electrode and the intersection point on the axis of the quartz glass tube;

[0009] A first gas interface is provided on the circumferential side wall of the tube body of the quartz glass tube between the first annular DC electrode and the second annular DC electrode. A second gas interface is provided on the circumferential side wall of the tube body of the quartz glass tube between the second annular DC electrode and the third annular DC electrode. A third gas interface is provided on the circumferential side wall of the tube body of the quartz glass tube between the left bottom surface of the left end of the quartz glass tube and the Nth annular DC electrode;

[0010] The first gas interface, the second gas interface, and the third gas interface are used for introducing and discharging the discharge gas and the chemical doping reagent gas inside the quartz glass tube and regulating the internal gas flow direction;

[0011] The RF discharge needle is applied with a DC bias potential of V, a frequency of f, and a peak-to-peak value of V p-p RF voltage. The first annular DC electrode, the second annular DC electrode (, ……, the (N - 1)th annular DC electrode, and the Nth annular DC electrode are respectively applied with a first DC potential V 1 , a second DC potential V 2 , ……, an (N - 1)th DC potential V N-1 , and an Nth DC potential V N . A discharge plasma is formed inside the tube body of the quartz glass tube. By adjusting the height relationship between the DC potentials V, V 1 , V 2 , ……, V N-1 , and V N , the migration direction of ions inside the quartz glass tube can be controlled;

[0012] The DC bias potential V is -10000 to 10000V, the frequency f is 1 to 3MHz, and the peak-to-peak value Vp-p is 100 to 300 V;

[0013] In the reaction reagent ion switching mode, the discharge gas enters the interior of the quartz glass tube through the first gas interface, the chemical doping reagent gas enters the interior of the quartz glass tube through the second gas interface, and the third gas interface is connected to the air extraction port of the vacuum pump. The air extraction speed of the vacuum pump is greater than the flow rate of the chemical doping reagent gas and less than the sum of the flow rates of the discharge gas and the chemical doping reagent gas;

[0014] The electric potential V and V N remain the same. In the positive ion mode, the DC electric potential V 1 < V 2 < V 3 < V 4 < …… < V N-1 < V N When this is the case, the positive reaction reagent ions flow out from the right end of the quartz glass tube. In the negative ion mode, the DC electric potential V 1 > V 2 > V 3 > V 4 > …… > V N-1 > V N , the negative reaction reagent ions flow out from the right end of the quartz glass tube. Changing the composition of the chemical doping reagent gas can change the composition of the positive and negative reaction reagent ions;

[0015] In the sample ionization mode switching mode, the first gas interface is in a sealed state, the discharge gas enters the interior of the quartz glass tube through the third gas interface, and the chemical doping reagent gas enters the interior of the quartz glass tube through the second gas interface;

[0016] The electric potential V and V 4 remain the same. In the positive ion mode, the DC electric potential V 1 > V 2 > V 3 > V 4 and V N > V N-1 > …… > V 4 , the excited state neutral molecules flow out from the right end of the quartz glass tube. In the negative ion mode, the DC electric potential V 1 < V 2 < V 3 < V 4 and V N < V N-1 < …… < V 4 , the excited state neutral molecules flow out from the right end of the quartz glass tube. Changing the composition of the chemical doping reagent gas can change the composition of the excited state neutral molecules;

[0017] The discharge ionization source serves as the ion source of the ion mobility spectrometer. The first annular DC electrode serves as the first annular electrode in the ionization region of the ion mobility tube along the direction from the ion source to the ion receiving electrode. Ions or excited-state neutral molecules flowing out of the right end of the quartz glass tube enter the ionization region of the ion mobility spectrometer and react with the sample molecules to be measured, generating sample product ions, which then enter the migration region of the ion mobility spectrometer through the ion gate of the ion mobility spectrometer that is periodically opened and are separated and detected.

[0018] The discharge ionization source for the ion mobility spectrometer provided by the present invention is designed based on the principle of low-temperature plasma discharge. The RF electrode of the discharge ionization source is a rod-shaped metal electrode placed inside the cavity of a single-end open quartz glass tube. The DC electrodes of the discharge ionization source are arranged in an array and at equal intervals on the outer wall surface of the discharge glass tube, and the potentials of each DC electrode can be independently adjusted, facilitating the control of the direction of the DC electric field in the ionization source and thus controlling the migration of ions. Additionally, multiple gas inlets are provided on the quartz glass tube, which can conveniently control the gas flow direction inside the quartz glass tube and the composition of the discharge gas. Based on the structural design of the array-type DC discharge electrodes and multiple gas inlets, the discharge ionization source uses air as the discharge gas, can achieve the switching of positive and negative ion modes, the switching of the reaction reagent ion components, and the switching of the sample ionization mode, has a simple structure, is portable in operation, and is suitable for ion mobility spectrometers.

[0019] The advantages of the present invention are:

[0020] The discharge ionization source provided by the present invention is designed based on the principle of low-temperature plasma discharge, has a simple structure, can directly use air as the discharge gas, realizes the rapid switching of positive and negative ion modes, reaction reagent ion components, and sample ionization modes, is portable in operation, and is very suitable for use in on-site detection ion mobility spectrometers.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings: Description of the Drawings

[0022] Figure 1 、Schematic diagram of the ion mobility tube structure based on the discharge ionization source disclosed in the present invention. Among them: (1-) RF discharge needle; (2) Quartz glass tube; (3-1) First DC electrode; (3-2) Second DC electrode; (3-3) Third DC electrode; (3-4) Fourth DC electrode; (3-5) Fifth DC electrode; (3-6-) Sixth DC electrode; (4) First gas inlet; (5) Second gas inlet; (6) Third gas inlet; (7) Ionization region; (8) Ion gate; (9) Migration region; (10) Ion receiving electrode; (11) Drift gas inlet; (12) Sample gas inlet; (13) Gas outlet.

[0023] Figure 2, When using purified air containing acetone, benzene, and toluene as chemical doping reagent gases respectively, the reaction reagent ions generated by the discharge ion source. (a) Purified air containing acetone as the chemical doping reagent gas, the generated ion mobility K 0 = 1.86 cm 2 V -1 s -1 of the reaction reagent ions; (b) Purified air containing benzene as the chemical doping reagent gas, the generated ion mobility K 0 = 2.22 cm 2 V -1 s -1 of the reaction reagent ions; (c) Purified air containing toluene as the chemical doping reagent gas, the generated ion mobility K 0 = 2.07 cm 2 V -1 s -1 of the reaction reagent ions.

[0024] Figure 3 , When using purified air containing toluene as the chemical doping reagent gas of the discharge ionization source, the ion mobility spectrometry response spectra of exhaled breath containing 20 ppbv propofol and 50 ppbv sevoflurane. (a) The response spectrum of propofol, and it can be observed that K 0 = 1.5 cm 2 V -1 s -1 of the product ions; (b) The response spectrum of sevoflurane, and basically no response signal can be observed.

[0025] Figure 4 , The structural diagram of the discharge ionization source disclosed in the present invention in the ion mobility tube. Wherein: (1-) Radio frequency discharge needle; (2) Quartz glass tube; (3-1) First DC electrode; (3-2) Second DC electrode; (3-3) Third DC electrode; (3-4) Fourth DC electrode; (3-5) Fifth DC electrode; (3-6-) Sixth DC electrode; (4) First gas interface; (5) Second gas interface; (6) Third gas interface. Detailed implementation mode

[0026] Example 1

[0027] The ion mobility tube device constructed based on the discharge ionization source disclosed in the present invention is as Figure 1 shown.

[0028] The quartz glass tube 2 is a cylindrical tube body with a sealed left end and an open right end. Along the direction from the right end to the left end of the quartz glass tube, first annular DC electrodes 3-1, second annular DC electrodes 3-2, ……, sixth annular DC electrodes 3-6 are sequentially sleeved on the outer wall surface of the quartz glass tube 2 at equal intervals. Among them, the first annular DC electrode 3-1 is close to the right end of the quartz glass tube 2, and the sixth annular DC electrode 3-6 is close to the left end of the quartz glass tube 2;

[0029] The RF discharge needle 1 is a round rod-shaped metal electrode. The left bottom surface inside the tube body of the quartz glass tube 2 is a hemispherical surface protruding to the left, and the center of the sphere of the hemispherical surface is located on the axis of the tube body. A through hole A is opened along the axis direction on the hemispherical bottom surface. One end of the RF discharge needle 1 passes through the through hole A and extends into the tube body, and the other end is outside the tube body. The outer wall surface of the RF discharge needle 1 is hermetically connected to the inner wall surface of the through hole A. The RF discharge needle 1 is coaxial with the quartz glass tube 2. The end plane of the end of the RF discharge needle 1 inside the tube body extends along the axis of the quartz glass tube 2 to the midpoint of the connection line of the intersection of the left end face of the third annular DC electrode 3-3, the right end face of the fourth annular DC electrode 3-4, and the axis of the quartz glass tube 2;

[0030] A first gas interface 4 is arranged on the circumferential side wall of the tube body of the quartz glass tube 2 between the first annular DC electrode 3-1 and the second annular DC electrode 3-2. A second gas interface 5 is arranged on the circumferential side wall of the tube body of the quartz glass tube 2 between the second annular DC electrode 3-2 and the third annular DC electrode 3-3. A third gas interface 6 is arranged on the circumferential side wall of the tube body between the bottom surface of the left end of the quartz glass tube and the sixth annular DC electrode 3-6.

[0031] The discharge ionization source is composed of the RF discharge needle 1, the quartz glass tube 2, and the DC electrodes 3-1 to 3-6 arranged in an array; the DC electrode 3-1 is simultaneously the first annular electrode in the ionization region of the ion migration tube; the RF discharge needle 1 is a tungsten metal rod with a diameter of 1 mm and a length of 50 mm. The wall thickness of the quartz glass tube is 1 mm, the inner diameter is 6 mm, and the length is 60 mm. One end of the RF discharge needle 1 is inserted into the quartz glass tube 2 along the axis and is hermetically connected at the left end face of the quartz glass tube 2. The length of the RF discharge needle 1 inside the quartz glass tube 2 is 30 mm; the DC electrodes 3-1 to 3-6 are all annular stainless steel electrodes with an inner diameter of 8 mm and an axial length of 3 mm, and are sleeved on the outer wall surface of the quartz glass tube 2 at equal intervals; the first gas interface 4, the second gas interface 5, and the third gas interface 6 on the quartz glass tube 2 are used for introducing and discharging the discharge gas and the chemical doping reagent gas, and regulating the gas flow direction inside the quartz glass tube 2;

[0032] The RF discharge needle 1 is applied with a DC bias potential of V, a frequency of f, and a peak-to-peak value of V p-pRF voltage, the first DC electrode 3-1, the second DC electrode 3-2, the third DC electrode 3-3, the fourth DC electrode 3-4, the fifth DC electrode 3-5, and the sixth DC electrode 3-6 are respectively applied with the first DC potential V 1 , the second DC potential V 2 , the third DC potential V 3 , the fourth DC potential V 4 , the fifth DC potential V 5 , and the sixth DC potential V 6 , to form a discharge plasma inside the quartz glass tube body, and by adjusting the height relationship between the DC potentials V, V 1 , V 2 , V 3 , V 4 , V 5 , and V 6 , the migration direction of ions inside the quartz glass tube can be controlled;

[0033] Both the ionization region 7 and the migration region 9 are composed of alternately stacked annular conductive electrode sheets with an axial length of 5 mm, an inner diameter of 18 mm, and an outer diameter of 30 mm, and annular insulating electrode sheets with an axial length of 5 mm, an inner diameter of 18 mm, and an outer diameter of 30 mm. The length of the ionization region 2 is 30 mm, and the length of the migration region 11 is 75 mm. An axial uniform DC electric field of 500 V / cm is set inside the ionization region 7 and the migration region 9; The ion gate 8 of the ion migration tube adopts a Bradbury-Neilsen type ion gate, which is made of metal wires with a diameter of 0.05 mm woven on a Teflon PCB electrode plate. The wire spacing is 0.3 mm. The metal wires on the ion gate are divided into two mutually insulated groups, and a 200 V potential difference is applied to achieve closing. The opening time of the ion gate is set to 150 μs; The ion receiving electrode 10 is a Faraday disk with a diameter of 6 mm, fixed on a metal shielding cylinder with an outer diameter of 30 mm;

[0034] The reaction reagent ions or excited state neutral molecules flowing out from the right end of the quartz glass tube 2 enter the ionization region 7, react with the sample molecules to be measured entering the ionization region 7 through the sample gas inlet 12, generate sample product ions, and then enter the migration region 9 through the periodically opened ion gate 8 to be separated and detected by the ion receiving electrode 10. The formed current signal is amplified by a microcurrent amplifier and then subjected to spectral sampling and recording by an oscilloscope.

[0035] The temperature of the ion migration tube is 100 °C. The drift gas is compressed air purified by passing through silica gel, molecular sieve, and activated carbon, with a flow rate of 500 mL / min. It enters the migration region 9 of the ion migration tube through the drift gas inlet 11, flows into the ionization region 7 through the ion gate 8, and then mixes with the sample gas entering the ionization region 7 through the sample gas inlet 12 and flows out of the ion migration tube through the outlet 13. The sample gas is purified air carrying the target molecules to be measured.

[0036] Example 2

[0037] When the discharge ionization source ion mobility tube disclosed in Example 1 operates in the positive ion mode, a DC electric field of 500 V / cm is applied in the ionization region 7 and the migration region 9 of the ion mobility tube; V is applied to the first DC electrode 3-1 1 = 5250 V, V is applied to the second DC electrode 3-2 2 = 5300 V, V is applied to the third DC electrode 3-3 3 = 5350 V, V is applied to the fourth DC electrode 3-4 4 = 5400 V, V is applied to the fifth DC electrode 3-4 5 = 5450 V, V is applied to the sixth DC electrode 3-6 6 = 5500 V, the RF discharge needle 1 is applied with a DC bias potential of V = 5500 V, a frequency of f = 1.5 MHz, and a peak-to-peak value of V p-p = 200 V of RF voltage; a discharge gas of 200 mL / min enters the quartz glass tube 2 through the first gas interface 4, a chemical doping reagent gas of 100 mL / min enters the quartz glass tube 2 through the second gas interface 5, the third gas interface 6 is connected to the suction port of the suction pump, and the suction flow rate is 200 mL / min; a sample gas of 200 mL / min enters the ionization region 7 through the sample gas inlet 12;

[0038] When the discharge gas is purified air filtered by molecular sieve and activated carbon, and purified air containing acetone, benzene, and toluene is used as the chemical doping reagent gas respectively, different reaction reagent ions generated by the discharge ion source can be detected, Figure 2 a is the reaction reagent ion with an ion mobility K 0 = 1.86 cm 2 V -1 s -1 generated when purified air containing acetone is used as the chemical doping reagent gas; Figure 2 b is the reaction reagent ion with an ion mobility K 0 = 2.22 cm 2 V -1 s -1 generated when purified air containing benzene is used as the chemical doping reagent gas; Figure 2 c is the reaction reagent ion with an ion mobility K 0 = 2.07 cm 2 V -1 s -1 generated when purified air containing toluene is used as the chemical doping reagent gas;

[0039] By regulating the reaction reagent ions generated by the discharge ionization source, highly selective detection of the target sample can be achieved.Figure 3 The ion mobility spectrometry diagram obtained by using toluene as the chemical doping reagent gas of the discharge ionization source and the exhaled breath containing 20 ppbv propofol and 50 ppbv sevoflurane as the sample gas is shown. Figure 3 As can be seen in a, propofol shows obvious signal peaks (K 0 = 1.5 cm 2 V -1 s -1 ). Figure 3 As can be seen in b, basically no response signal of sevoflurane can be observed. That is, the reaction reagent ions (K 0 = 2.07 cm 2 V -1 s -1 ) formed by using toluene can achieve highly selective detection of trace propofol in the exhaled breath of patients under combined anesthesia of propofol and sevoflurane.

[0040] When the ion mobility spectrometry works in the negative ion mode, a voltage of V 1 = -5250 V is applied to the first DC electrode 3-1, a voltage of V 2 = -5300 V is applied to the second DC electrode 3-2, a voltage of V 3 = -5350 V is applied to the third DC electrode 3-3, a voltage of V 4 = -5400 V is applied to the fourth DC electrode 3-4, a voltage of V 5 = -5450 V is applied to the fifth DC electrode 3-4, a voltage of V 6 = -5500 V is applied to the sixth DC electrode 3-6, and a DC bias potential of V = -5500 V is applied to the RF discharge needle 1, so that the discharge ionization source ion mobility tube can work normally.

[0041] Example 3

[0042] When the discharge ionization source ion mobility tube disclosed in Example 1 works in the positive ion mode, a DC electric field of 500 V / cm is applied in the ionization region 7 and the migration region 9 of the ion mobility tube; a voltage of V 1 = 5400 V is applied to the first DC electrode 3-1, a voltage of V 2 = 5350 V is applied to the second DC electrode 3-2, a voltage of V 3 = 5300 V is applied to the third DC electrode 3-3, a voltage of V 4 = 5250 V is applied to the fourth DC electrode 3-4, a voltage of V 5 = 5300 V is applied to the fifth DC electrode 3-4, a voltage of V 6 = 5350 V is applied to the sixth DC electrode 3-6, and a DC bias potential of V = 5250 V, a frequency of f = 1.5 MHz and a peak-to-peak value of V p-p= 200 V RF voltage; the first gas interface 4 is sealed, and a discharge gas of 200 mL / min enters the quartz glass tube 2 through the third gas interface 6, a chemical doping reagent gas of 100 mL / min enters the quartz glass tube 2 through the second gas interface 5, and a sample gas of 200 mL / min enters the ionization region 7 through the sample gas inlet 12;

[0043] When the discharge gas is high-purity nitrogen and the sample gas is purified air filtered by molecular sieve and activated carbon, and helium and argon are used as chemical doping reagent gases respectively, the discharge ion source generates high-energy excited state neutral particles, and the neutral particles react with trace water in the sample gas to generate hydrated hydrogen ions (H 2 O) n H + , which can undergo a molecular ion reaction with volatile organic compounds with high proton affinity to form product ions.

Claims

1. A discharge ionization source for ion mobility spectrometry, characterized in that: it includes a radio frequency discharge needle (1), a quartz glass tube (2) and a DC electrode (3); The quartz glass tube (2) is a cylindrical tube body with a closed left end and an open right end. Along the direction from the right end to the left end of the quartz glass tube (2), a first annular DC electrode (3-1), a second annular DC electrode (3-2),..., a (N-1)th annular DC electrode (3-(N-1)) and an Nth annular DC electrode (3-N) are successively sleeved on the outer wall surface of the quartz glass tube (2) at equal intervals. N is a positive integer greater than or equal to 4. Among them, the first annular DC electrode (3-1) is close to the right end of the quartz glass tube (2), and the Nth annular DC electrode (3-N) is close to the left end of the quartz glass tube (2); The radio frequency discharge needle (1) is a round rod-shaped metal electrode. The left bottom surface inside the tube body of the quartz glass tube (2) is a hemispherical surface protruding to the left. The center of the sphere of the hemispherical surface is located on the axis of the tube body. A through hole A is opened along the axis direction on the hemispherical bottom surface. One end of the radio frequency discharge needle (1) passes through the through hole A and extends into the tube body, and the other end is outside the tube body. The outer wall surface of the radio frequency discharge needle (1) is hermetically connected to the inner wall surface of the through hole A. The radio frequency discharge needle (1) is coaxial with the quartz glass tube (2). The end plane of the radio frequency discharge needle (1) at the end inside the tube body extends along the axis of the quartz glass tube (2) to the midpoint of the connection line between the left end face of the third annular DC electrode (3-3) and the right end face of the fourth annular DC electrode (3-4) and the intersection point on the axis of the quartz glass tube (2); A first gas interface (4) is provided on the circumferential side wall of the tube body of the quartz glass tube (2) between the first annular DC electrode (3-1) and the second annular DC electrode (3-2). A second gas interface (5) is provided on the circumferential side wall of the tube body of the quartz glass tube (2) between the second annular DC electrode (3-2) and the third annular DC electrode (3-3). A third gas interface (6) is provided on the circumferential side wall of the tube body between the bottom surface at the left end of the quartz glass tube (2) and the Nth annular DC electrode (3-N).

2. The discharge ionization source according to claim 1, characterized in that: The first gas interface (4), the second gas interface (5) and the third gas interface (6) are used for introducing and extracting the discharge gas and the chemical doping reagent gas inside the quartz glass tube (2) and regulating the internal gas flow direction.

3. The discharge ionization source according to claim 1, characterized in that: The radio frequency discharge needle (1) applies a DC bias potential of V, a frequency of f, and a radio frequency voltage with a peak-to-peak value of V p-p to the first annular DC electrode (3-1), the second annular DC electrode (3-2), ……, the (N-1)th annular DC electrode (3-N-1), and the Nth annular DC electrode (3-N) respectively apply the first DC potential V 1 , the second DC potential V 2 , ……, the (N-1)th DC potential V N-1 and the Nth DC potential V N , to form a discharge plasma inside the tube body of the quartz glass tube (2). By adjusting the height relationship between the DC potentials V, V 1 , V 2 , ……, V N-1 and V N , the migration direction of ions inside the quartz glass tube (2) can be controlled; The DC bias potential V is -10000 to 10000 V, the frequency f is 1 to 3 MHz, and the peak-to-peak value V p-p is 100 to 300 V.

4. The discharge ionization source according to any one of claims 1-3, characterized in that: In the reaction reagent ion switching mode, the discharge gas enters the inside of the quartz glass tube (2) through the first gas interface (4), the chemical doping reagent gas enters the inside of the quartz glass tube (2) through the second gas interface (5), the third gas interface (6) is communicated with the air extraction port of the vacuum pump, and the air extraction speed of the vacuum pump is greater than the flow rate of the chemical doping reagent gas and less than the sum of the flow rates of the discharge gas and the chemical doping reagent gas; The potential V and V N remain the same. In the positive ion mode, the DC potential V 1 <V 2 <V 3 <V 4 <……<V N-1 <V N When this is the case, the positive reaction reagent ions flow out from the right end of the quartz glass tube (2). In the negative ion mode, the DC potential V 1 >V 2 >V 3 >V 4 >……>V N-1 >V N , and the negative reaction reagent ions flow out from the right end of the quartz glass tube (2). Changing the composition of the chemical doping reagent gas can change the composition of the positive and negative reaction reagent ions.

5. The discharge ionization source according to any one of claims 1-3, characterized in that: In the sample ionization mode switching mode, the first gas interface (4) is in a sealed state, the discharge gas enters the interior of the quartz glass tube (2) through the third gas interface (6), and the chemical doping reagent gas enters the interior of the quartz glass tube (2) through the second gas interface (5). The electric potential V and V 4 remain the same. In the positive ion mode, the DC electric potential V 1 > V 2 > V 3 > V 4 and V N > V N-1 >... > V 4 , and the excited state neutral molecules flow out from the right end of the fused silica glass tube (2). In the negative ion mode, the DC electric potential V 1 < V 2 < V 3 < V 4 and V N < V N-1 <... < V 4 , and the excited state neutral molecules flow out from the right end of the fused silica glass tube (2). Changing the composition of the chemical doping reagent gas can change the composition of the excited state neutral molecules.

6. Application of the discharge ionization source according to any one of claims 1-6, characterized in that: The discharge ionization source according to any one of claims 1-6 is used as an ion source of an ion mobility spectrometer. The first annular DC electrode (3-1) serves as the first annular electrode in the ionization region of the ion mobility tube along the direction from the ion source to the ion receiving electrode. Ions or excited state neutral molecules flowing out of the right end of the quartz glass tube (2) enter the ionization region of the ion mobility spectrometer and react with the sample molecules to be measured to generate sample product ions, and then enter the migration region of the ion mobility spectrometer through the ion gate of the ion mobility spectrometer that is periodically opened and are separated and detected.

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