Corona discharge ion mobility spectrometer

Abstract

The invention discloses a corona discharge ion mobility spectrometer, which relates to the technical field of analytical chemistry instruments and comprises a corona discharge assembly, a reverse field ion gate structure, an ion migration assembly, a sample gas inlet, a shielding grid mesh and a Faraday detection plate. The corona discharge assembly comprises a corona discharge needle and at least three ion reaction area electrode rings which are sequentially distributed at intervals. The reverse field ion gate structure comprises a first grid mesh, a second grid mesh and a third grid mesh which are distributed at intervals in the axial direction and can be connected with different voltages, and the reaction area is located between the first grid mesh and the second grid mesh. The ion migration assembly comprises a plurality of ion migration region electrode rings which are coaxially arranged. The electric field is improved through the arrangement of the grid meshes, the area between the first grid mesh and the second grid mesh of the reverse field ion gate serves as the reaction area, the original reaction area is removed, miniaturization of the drift tube is facilitated, and meanwhile the sensitivity and the resolution ratio under a complex matrix are improved.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry instrumentation technology, and in particular to a corona discharge ion mobility spectrometer. Background Technology

[0002] Ion mobility spectrometry (IMA) is a highly efficient and rapid gas-phase ion separation and detection technology, widely used in fields such as chemical warfare agents, explosives, drug detection, environmental monitoring, and biomedicine. Its basic principle is to ionize sample molecules at atmospheric or near-atmospheric pressure. These ions then drift in a weak electric field, and separation is achieved due to the different migration rates of different ions within the electric field, ultimately leading to detection by a detector.

[0003] Traditional ion mobility spectrometry, such as ionization using radioactive sources (e.g., Ni-63), while technically mature, faces numerous limitations due to concerns about the management, transportation, and disposal of radioactive materials, as well as public safety. To overcome these drawbacks, non-radioactive ionization sources, such as corona discharge ionization sources, have gradually become a research hotspot. Corona discharge ionization technology offers advantages such as high ionization efficiency, strong controllability, and no radioactive hazards.

[0004] However, existing corona discharge ion mobility spectrometers still require improvement in structural design and performance. Firstly, corona discharge ion mobility spectrometers belong to the time-of-migration ion mobility spectrometry (DT-IMS) category. DT-IMS spectrometers typically have three spatially independent regions: the reaction region, the ion gate region, and the migration region. The presence of the ion gate region necessitates a relatively long drift tube in existing corona discharge ion mobility spectrometers, directly resulting in a bulky and less compact overall structure, limiting their application in space-constrained scenarios such as rapid on-site detection and portable devices. While some studies have attempted to shorten the drift distance by modifying the electric field design, this often comes at the cost of performance.

[0005] Secondly, in terms of performance, existing corona discharge ion mobility spectrometers still have room for improvement in sensitivity and resolution under complex matrix environments. Insufficient sensitivity may lead to missed detection of trace substances, while low resolution will affect the accurate differentiation and identification of different components in mixed samples, increasing the risk of misjudgment. Therefore, how to achieve and surpass the sensitivity and resolution of traditionally sized instruments while reducing instrument size, or even in a more compact structure, is a goal that those skilled in the art continue to pursue. Summary of the Invention

[0006] The purpose of this invention is to provide a corona discharge ion mobility spectrometer to solve the problems existing in the prior art and reduce the size of the corona discharge ion mobility spectrometer.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a corona discharge ion mobility spectrometer, comprising: case; A corona discharge assembly, comprising a corona discharge needle fixed in a corona needle hole in the housing and a first through hole coaxial with the corona discharge needle and disposed on a first electrode ring, wherein the tip of the corona discharge needle is close to and directly faces the first through hole. At least two ion reaction zone electrode rings are sequentially spaced along the axial direction of the corona discharge needle, and all of the ion reaction zone electrode rings are located on the side of the first electrode ring away from the corona discharge needle. A reverse-field ion gate structure includes a first grid, a second grid, and a third grid spaced apart along the axial direction of the corona discharge needle. The reaction region of the corona discharge ion mobility spectrometer is located between the first grid and the second grid. The first grid is closer to the corona discharge assembly than the third grid. The first grid, the second grid, and the third grid are configured to be connected to different voltages, respectively. An ion migration assembly includes a plurality of ion migration region electrode rings that are sequentially spaced along the axial direction of a corona discharge needle; all of the ion migration region electrode rings are coaxially arranged with all of the ion reaction region electrode rings, and all of the ion reaction region electrode rings are located between the corona discharge needle and the ion migration assembly. A sample inlet connected to the reaction zone is used to introduce sample gas into the reaction zone. A shielding grid is disposed at one end of the ion migration region in the ion migration assembly that is away from the corona discharge assembly. A Faraday detection plate, wherein the Faraday detection plate is located on the side of the shielding grid away from the corona discharge assembly; A buffer gas inlet is fixed on the housing, and the buffer gas inlet is connected to the side of the ion migration region of the corona discharge ion mobility spectrometer away from the reaction region. A drift gas outlet is fixed on the housing, and the drift gas outlet communicates with the corona needle hole.

[0008] Preferably, the first grid is electrically connected to the first electrode ring, and the second grid and the third grid are respectively electrically connected to one of the ion reaction region electrode rings, and the ion reaction region electrode rings electrically connected to the second grid and the third grid are different from each other.

[0009] Preferably, the first electrode ring is further provided with a second through hole, the diameter of the second through hole is larger than the diameter of the first through hole, one end of the second through hole is connected to the first through hole, and the other end is close to the first grid.

[0010] Preferably, the first grid is bonded to the end face of the first electrode ring away from the corona discharge needle using graphite conductive adhesive.

[0011] Preferably, the electrode ring of the ion reaction region adjacent to the first electrode ring is a second electrode ring, and the second grid is bonded to the end face of the second electrode ring away from the first electrode ring by graphite conductive adhesive. The sample air inlet is located on the second electrode ring.

[0012] Preferably, the ion reaction region electrode ring located on the side of the second electrode ring away from the first electrode ring and adjacent to the second electrode ring is a third electrode ring, and the third grid is electrically connected to the end face of the third electrode ring away from the second electrode ring through graphite conductive adhesive.

[0013] Preferably, the length of the reaction zone is changed by replacing the second electrode ring with one of different axial lengths.

[0014] Preferably, the thickness of the first electrode ring is 2mm to 5mm.

[0015] Preferably, the first electrode ring, all the electrode rings in the ion reaction region, and all the electrode rings in the ion migration region are all referred to as electrode rings. All the electrode rings are coaxial, and an annular insulating pad is sandwiched between any two adjacent electrode rings.

[0016] Preferably, the number of electrode rings in the ion reaction zone is two.

[0017] The present invention achieves the following technical effects compared to the prior art: The corona discharge ion mobility spectrometer of this invention optimizes the electric field distribution and ion control in the reaction and ion migration regions by combining at least two electrode rings in the ion reaction region with a specifically configured inverse field ion gate structure. This integrated design can effectively shorten the required ion drift path length while ensuring or even improving ion separation performance, ultimately significantly reducing the overall size and dimensions of the instrument, making it more suitable for applications with strict space requirements, such as rapid on-site detection and portable devices.

[0018] The first grid in the inverse field ion gate structure can improve the electric field distortion generated by the corona discharge needle and effectively suppress the diffusion effect during ion implantation, preventing a large number of ions from colliding with the inner wall of the electrode ring in the ion reaction zone, reducing ion loss, thereby improving the efficiency of indirect ionization of sample gas in the reaction zone, ensuring the generation of enough ions, and improving the sensitivity of the device.

[0019] The inverse field ion gate not only improves the electric field distortion but also makes the electric field tend to be uniform, ensuring that different ions can move at different speeds and arrive at the Faraday detection plate in sequence, thereby improving the resolution of the device.

[0020] The length of the reaction zone can be changed by replacing the second electrode ring with one of different axial lengths, providing a simple and effective means of adjusting ionization conditions for different sample characteristics, thus enhancing the instrument's adaptability and performance optimization potential. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the corona discharge ion mobility spectrometer of the present invention; In the figure: 1. Shell; 2. Corona discharge needle; 3. First electrode ring; 4. Second electrode ring; 5. First through hole; 6. Second through hole; 7. Drift gas outlet; 8. First grid; 9. Second grid; 10. Third grid; 11. Third electrode ring; 12. Ion migration region electrode ring; 13. Shielding grid; 14. Faraday detection plate; 15. Buffer gas inlet; 16. Sample gas inlet. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The purpose of this invention is to provide a corona discharge ion mobility spectrometer to solve the problems existing in the prior art and reduce the size of the corona discharge ion mobility spectrometer.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, this embodiment provides a corona discharge ion mobility spectrometer, including: Casing 1; The corona discharge assembly includes a corona discharge needle 2 fixed in the corona needle hole of the housing 1 and a first through hole 5 coaxial with the corona discharge needle 2 and disposed on the first electrode ring 3, wherein the tip of the corona discharge needle 2 is close to and directly faces the first through hole 5. Two ion reaction zone electrode rings are distributed sequentially and spaced apart along the axial direction of the corona discharge needle 2, and all ion reaction zone electrode rings are located on the side of the first electrode ring 3 away from the corona discharge needle 2; the space formed by the hollow holes of all ion reaction zone electrode rings constitutes the ion reaction zone. The inverse field ion gate structure includes a first grid 8, a second grid 9, and a third grid 10 spaced apart along the axial direction of the corona discharge needle 2. The reaction region of the corona discharge ion mobility spectrometer is located between the first grid 8 and the second grid 9, with the first grid 8 being closer to the corona discharge assembly than the third grid 10. The first grid 8, the second grid 9, and the third grid 10 are configured to be connected to different voltages respectively. The ion migration assembly includes multiple ion migration region electrode rings 12 that are sequentially spaced along the axial direction of the corona discharge needle 2; all ion migration region electrode rings 12 are coaxially arranged with all ion reaction region electrode rings, and all ion reaction region electrode rings are located between the corona discharge needle 2 and the ion migration assembly; the space formed by the hollow holes of all ion migration region electrode rings 12 constitutes the ion migration region. The sample inlet 16 is connected to the reaction zone and is used to introduce sample gas into the reaction zone. A shielding grid 13 is disposed at the end of the ion migration region in the ion migration assembly that is away from the corona discharge assembly. Faraday detection plate 14 is located on the side of shielding grid 13 away from corona discharge assembly; A buffer gas inlet 15 is fixed on the housing 1, and the buffer gas inlet 15 is connected to the side of the ion migration region of the corona discharge ion mobility spectrometer away from the reaction region. The drift gas outlet 7 is fixed on the housing 1 and is connected to the corona needle hole.

[0027] In this embodiment, the first grid 8 is electrically connected to the first electrode ring 3, and the second grid 9 and the third grid 10 are respectively electrically connected to an ion reaction region electrode ring, and the ion reaction region electrode rings electrically connected to the second grid 9 and the third grid 10 are different from each other.

[0028] In the optional scheme of this embodiment, a more preferred embodiment is that the first electrode ring 3 is further provided with a second through hole 6, the diameter of the second through hole 6 is larger than the diameter of the first through hole 5, one end of the second through hole 6 is connected to the first through hole 5, and the other end is close to the first grid 8.

[0029] In this embodiment, the first grid 8 is bonded to the end face of the first electrode ring 3 away from the corona discharge needle 2 by graphite conductive adhesive. The voltage of the first grid 8 and the first electrode ring 3 are equal. By connecting the first electrode ring 3 to an external first high-voltage electrode, a high voltage is applied to the first electrode ring 3 and the first grid 8.

[0030] In this embodiment, the ion reaction region electrode ring adjacent to the first electrode ring 3 is the second electrode ring 4. The second grid 9 is bonded to the end face of the second electrode ring 4 away from the first electrode ring 3 by graphite conductive adhesive. The voltage of the second grid 9 and the second electrode ring 4 are equal. By connecting the second electrode ring 4 to an external second high voltage electrode, a high voltage is applied to the second electrode ring 4 and the second grid 9. The sample inlet 16 is located on the second electrode ring 4, that is, the sample inlet 16 passes through the second electrode ring 4 and communicates with the reaction zone.

[0031] In this embodiment, the ion reaction region electrode ring located on the side of the second electrode ring 4 away from the first electrode ring 3 and adjacent to the second electrode ring 4 is the third electrode ring 11. The third grid 10 is electrically connected to the end face of the third electrode ring 11 away from the second electrode ring 4 through graphite conductive adhesive. The voltage of the third grid 10 and the third electrode ring 11 is equal. By connecting the third electrode ring 11 to an external third high-voltage electrode, a high voltage is applied to the third electrode ring 11 and the third grid 10.

[0032] In the optional schemes of this embodiment, it is more preferred to change the length of the reaction zone by replacing the second electrode ring 4 with one of different axial lengths. By replacing the second electrode ring 4 with one of different axial lengths, the length of the reaction zone can be changed, providing a simple and effective means of adjusting the ionization conditions for different sample characteristics, thereby enhancing the adaptability and performance optimization potential of the instrument.

[0033] In the optional schemes of this embodiment, it is more preferred that the thickness of the first electrode ring 3 is 2mm to 5mm. By using the first electrode ring 3 with different thicknesses, the distance between the first grid 8 and the tip of the corona discharge needle 2 can be changed, thereby achieving different corona discharge effects.

[0034] In the optional schemes of this embodiment, it is more preferred that the first electrode ring 3, the electrode ring of all ion reaction regions and the electrode ring of all ion migration regions 12 are all referred to as electrode rings, all electrode rings are coaxial, and an annular insulating gasket is sandwiched between any two adjacent electrode rings.

[0035] The specific working principle of the corona discharge ion mobility spectrometer in this embodiment is as follows: A first high voltage is applied to the corona discharge needle 2, a second high voltage is applied to the first electrode ring 3, and the voltage of the first grid 8 is the same as the voltage of the first electrode ring 3. A third high voltage is applied to the second electrode ring 4, and the voltage of the second grid 9 is the same as the voltage of the second electrode ring 4. A fourth high voltage is applied to the third electrode ring 11, and the voltage of the third grid 10 is the same as the voltage of the third electrode ring 11. The first high voltage is much higher than the second high voltage, and the second and fourth high voltages are both lower than the third high voltage. A high-voltage electric field is formed between the tip of the corona discharge needle 2 and the first electrode ring 3, causing the air between the tip of the corona discharge needle 2 and the first electrode ring 3 to... Neutral molecules ionize, and the positive ions generated by ionization pass through the first grid 8 and enter the reaction zone. In the reaction zone, the positive ions react with the sample gas entering through the sample inlet 16, causing the sample gas molecules to ionize. That is, the positive ions generated by ionization will indirectly ionize the sample gas in the reaction zone, producing ionization products of the sample gas. The ionization products of the sample gas move towards the second grid 9 under the action of the applied electric field. However, since the voltage of the second grid 9 is greater than the voltage of the first grid 8, all the positive ions and ionization products of the sample gas will gradually stop moving when they reach a position close to the second grid 9. After the sample gas is indirectly ionized for a set time period through the above process, the voltage of the second electrode ring 4 is changed to the fifth high voltage, and the second high voltage is greater than the fifth high voltage, and the fifth high voltage is greater than the fourth high voltage, so that all positive ions in the reaction zone and the ionization products of the sample gas pass through the second grid 9 and move from the second grid 9 toward the third grid 10. After passing through the third grid 10, they move toward the Faraday detection plate 14 in the ion migration zone. Before reaching the Faraday detection plate 14, the shielding grid 13 eliminates the induced charges that may affect the signal generated by the ion clusters (referring to all positive ions and the ionization products of the sample gas) on the Faraday detection plate 14. Since the sample gas introduced through the sample inlet 16 is generally continuously injected, some sample gas cannot be ionized during the actual reaction process. If this part of the sample gas is not processed in time, it will affect the detection effect. The buffer gas entering from the buffer gas inlet 15 can carry away unreacted sample gas and other impurity gases from the drift gas outlet 7. It is worth noting that the collision between buffer gas molecules and ions is the basis of IMS operation. The mobility directly depends on the collision cross section and momentum transfer of ion-buffer gas molecules, thereby converting the size, shape and mass information of ions into measurable migration time. High-purity buffer gas can act as a good insulator, playing a role in maintaining a stable electric field. In addition, optimizing the flow rate and direction of buffer gas can overcome the diffusion effect of ions to a certain extent, playing a focusing role. Dry and inert buffer gas can reduce ion-molecule reactions and reduce possible ion loss, that is, reduce the impact on resolution sensitivity.

[0036] It is worth noting that the addition of a grid after the first electrode ring 3 helps to reduce the distortion of the electric field near the corona discharge needle 2 caused by the high voltage there. If the high voltage at the corona discharge needle 2 penetrates into the ion reaction zone, it will affect the uniform electric field of the ion reaction zone. The specific reason is as follows: The first electrode ring 3 and the first grid 8 are electrically connected and have the same voltage, thus forming an equipotential shield and field reshaping between them. Without the first grid 8, the potential changes continuously from the high-potential corona discharge needle 2 to the lower-potential first electrode ring 3, and then to the subsequent drift region. The extreme electric field distortion at the tip of the corona needle would affect the subsequent region through this continuity, causing severe distortion of the equipotential surface. The first grid 8 acts as a "buffer zone" or "transition region," limiting and attenuating the electric field distortion within this transition region, thereby protecting the uniformity of the subsequent drift electric field. According to the basic principles of electrostatics, the entire surface of a conductor is an equipotential surface. Without the first grid 8, the shape of the equipotential surface near the first electrode ring 3 is unknown and distorted, strongly influenced by the intense field of the corona discharge needle. However, with the first grid 8, the electric field lines emitted by the corona discharge needle 2 aim to find a surface with a lower potential. Before reaching the first grid 8, they pass through the space defined by the first electrode ring 3. The presence of the first grid 8 (denoted by potential V), together with the first electrode ring 3 (denoted by potential V), constitutes an extended and defined equipotential region. This region "absorbs" and "collects" the electric field lines from the corona region, thereby improving the distortion of the electric field and making the electric field more uniform.

[0037] The first grid 8 in the inverse-field ion gate structure can improve the electric field distortion generated by the corona discharge needle 2 and effectively suppress the diffusion effect during ion implantation, preventing a large number of ions from colliding with the inner wall of the electrode ring in the ion reaction zone, reducing ion loss, and thus improving the efficiency of indirect ionization of the sample gas in the reaction zone, ensuring the generation of a sufficient number of ions and improving the sensitivity of the device. While improving the electric field distortion, the inverse-field ion gate can also make the electric field tend towards a uniform electric field, ensuring that different ions can have different movement velocities and arrive at the Faraday detection plate 14 sequentially, thereby improving the resolution of the device.

[0038] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A corona discharge ion mobility spectrometer, characterized in that, include: case; A corona discharge assembly, comprising a corona discharge needle fixed in a corona needle hole in the housing and a first through hole coaxial with the corona discharge needle and disposed on a first electrode ring, wherein the tip of the corona discharge needle is close to and directly faces the first through hole. At least two ion reaction zone electrode rings are sequentially spaced along the axial direction of the corona discharge needle, and all of the ion reaction zone electrode rings are located on the side of the first electrode ring away from the corona discharge needle. A reverse-field ion gate structure includes a first grid, a second grid, and a third grid spaced apart along the axial direction of the corona discharge needle. The reaction region of the corona discharge ion mobility spectrometer is located between the first grid and the second grid. The first grid is closer to the corona discharge assembly than the third grid. The first grid, the second grid, and the third grid are configured to be connected to different voltages, respectively. An ion migration assembly includes a plurality of ion migration region electrode rings that are sequentially spaced along the axial direction of a corona discharge needle; all of the ion migration region electrode rings are coaxially arranged with all of the ion reaction region electrode rings, and all of the ion reaction region electrode rings are located between the corona discharge needle and the ion migration assembly. A sample inlet connected to the reaction zone is used to introduce sample gas into the reaction zone. A shielding grid is disposed at one end of the ion migration region in the ion migration assembly that is away from the corona discharge assembly. A Faraday detection plate, wherein the Faraday detection plate is located on the side of the shielding grid away from the corona discharge assembly; A buffer gas inlet is fixed on the housing, and the buffer gas inlet is connected to the side of the ion migration region of the corona discharge ion mobility spectrometer away from the reaction region. A drift gas outlet is fixed on the housing, and the drift gas outlet communicates with the corona needle hole.

2. The corona discharge ion mobility spectrometer according to claim 1, characterized in that: The first grid is electrically connected to the first electrode ring, and the second grid and the third grid are respectively electrically connected to one of the ion reaction region electrode rings, and the ion reaction region electrode rings electrically connected to the second grid and the third grid are different from each other.

3. The corona discharge ion mobility spectrometer according to claim 1, characterized in that: The first electrode ring is also provided with a second through hole, the diameter of the second through hole is larger than the diameter of the first through hole, one end of the second through hole is connected to the first through hole, and the other end is close to the first grid.

4. The corona discharge ion mobility spectrometer according to claim 3, characterized in that: The first grid is bonded to the end face of the first electrode ring away from the corona discharge needle by graphite conductive adhesive.

5. The corona discharge ion mobility spectrometer according to claim 3, characterized in that: The ion reaction region electrode ring adjacent to the first electrode ring is a second electrode ring, and the second grid is bonded to the end face of the second electrode ring away from the first electrode ring by graphite conductive adhesive. The sample air inlet is located on the second electrode ring.

6. The corona discharge ion mobility spectrometer according to claim 5, characterized in that: The ion reaction region electrode ring located on the side of the second electrode ring away from the first electrode ring and adjacent to the second electrode ring is the third electrode ring. The third grid is electrically connected to the end face of the third electrode ring away from the second electrode ring through graphite conductive adhesive.

7. The corona discharge ion mobility spectrometer according to claim 5, characterized in that: The length of the reaction zone is changed by replacing the second electrode ring with one of different axial lengths.

8. The corona discharge ion mobility spectrometer according to claim 1, characterized in that: The thickness of the first electrode ring is 2mm to 5mm.

9. The corona discharge ion mobility spectrometer according to claim 1, characterized in that: The first electrode ring, all the electrode rings in the ion reaction region, and all the electrode rings in the ion migration region are all referred to as electrode rings. All the electrode rings are coaxial, and an annular insulating pad is sandwiched between any two adjacent electrode rings.

10. The corona discharge ion mobility spectrometer according to claim 1, characterized in that: The number of electrode rings in the ion reaction zone is two.

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