Aerosol thermal desorption ion source

Abstract

The application provides an aerosol thermal desorption ion source, which comprises a flash evaporator for receiving a particle beam transmitted along a first direction and heating and vaporizing particles in the particle beam to generate gas molecules; and a filament for releasing electrons to ionize the gas molecules to generate ions; the flash evaporator has a length along the first direction, a width along a second direction, and a thickness along a third direction; the first direction, the second direction and the third direction intersect each other; in the first direction, a cross section of the flash evaporator perpendicular to the first direction is rectangular; in the second direction, the width of the flash evaporator is smaller than the irradiation range of the filament; and in the third direction, the filament is arranged on both sides of the flash evaporator; by using the device, the shape of the gas flow generated by the flash evaporator can be changed, the coincidence degree of the distribution area of the gas and the transmission area of the directional electron beam is improved, and the ionization efficiency of the gas molecules is improved.

Description

Technical Field

[0001] This invention relates to the field of environmental monitoring technology, and more specifically, to an aerosol thermal desorption ion source. Background Technology

[0002] Atmospheric aerosols have a significant impact on global climate change, environmental pollution, and public health. Their chemical composition directly affects their optical properties, toxicological effects, and environmental behavior. However, current routine detection methods for aerosol chemical components largely rely on offline sampling and laboratory analysis, which have limitations such as low temporal resolution, analytical lag, and difficulty in capturing rapid atmospheric changes. In particular, there is a lack of highly sensitive, real-time quantitative detection methods for studying low-concentration organic components and transient pollution processes.

[0003] Currently, the primary device for real-time quantitative measurement of aerosol chemical composition is the time-of-flight mass spectrometer (TOF-MS). An aerosol mass spectrometer consists of a pneumatic sample introduction system, a high-vacuum ion source, an ionization chamber, an ion transport system, and a TOF-MS analysis area. The instrument's main principle is as follows: aerosols enter the vacuum chamber through an aerodynamic lens and are focused into a particle beam. This particle beam strikes a flash evaporator, where volatile components evaporate under heat, forming gaseous substances. These gaseous substances ionize under the influence of a filament, forming different fragment ions. The TOF composition is measured by measuring these fragment ions to generate mass spectrometry information. This instrument enables continuous, high-temporal-resolution measurement of non-volatile or low-volatile components in atmospheric aerosols. It not only possesses high sensitivity and a wide dynamic range but also can track rapid fluctuations in pollutants in real time, providing strong technical support for air quality monitoring, pollution control, and scientific research. The thermal desorption evaporator and ion source are the most crucial core components of the instrument, their performance directly affecting the uniformity and efficiency of gas molecule release, as well as the effectiveness of subsequent electron bombardment ionization. However, currently commercially available aerosol mass spectrometers all use cylindrical flash evaporators as pyrolysis devices. Their curved structure exhibits a shielding effect during electron beam irradiation, resulting in insufficient spatial overlap between electrons and gas molecules produced by pyrolysis, thus limiting the improvement of ionization efficiency. This shielding effect causes a large number of unionized neutral molecules to enter the subsequent ion transport structure, increasing the background signal and noise load of the mass spectrometer, affecting detection sensitivity and quantitative accuracy. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an aerosol thermal desorption ion source to overcome the limitation of the electron beam ionization effect of the existing thermal desorption ion source.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: an aerosol thermal desorption ion source, comprising: a flash evaporator for receiving a particle bundle transported along a first direction and heating and vaporizing the particles in the particle bundle to generate gas molecules; a filament for releasing electrons to ionize the gas molecules to generate ions; the flash evaporator having a length along the first direction, a width along a second direction, and a thickness along a third direction; the first direction, the second direction, and the third direction intersect each other; in the first direction, the cross-section of the flash evaporator perpendicular to the first direction is rectangular; in the second direction, the width of the flash evaporator is smaller than the irradiation range of the filament; in the third direction, the filament is disposed on both sides of the flash evaporator.

[0006] In one embodiment, in the first direction, the flash evaporator is provided with a first end and a second end in sequence along the direction of particle bundle transmission; a groove for accommodating particles is provided at the first end, and the groove extends into the interior of the flash evaporator along the first direction.

[0007] In one embodiment, the bottom surface of the groove intersects with the first direction; the bottom surface of the groove is provided with a plurality of limiting grooves for reducing particle reflection.

[0008] In one embodiment, the limiting groove has a pyramidal structure; the width of the limiting groove gradually decreases along the transmission direction of the particle beam.

[0009] In one embodiment, the limiting groove is a regular square pyramid structure, and there is a first included angle A1 between two opposite sides of the limiting groove; the angle of the first included angle A1 is between 0° and 90°.

[0010] In one embodiment, the width W of the flash evaporator in the second direction satisfies: 0.5mm < W < 2mm; and the thickness D of the flash evaporator in the third direction satisfies: 2mm < D < 4mm.

[0011] In one embodiment, the flash evaporator is made of porous tungsten material.

[0012] In one embodiment, it further includes: a gas gathering hood, the gas gathering hood having a cylindrical structure, the axis of the gas gathering hood being parallel to the first direction; the gas gathering hood being disposed around the flash evaporator; and in the third direction, the gas gathering hood having an electron channel opposite to it; electrons released by the filament being able to enter the interior of the gas gathering hood through the electron channel.

[0013] In one embodiment, the gas gathering hood is hexagonal prism-shaped, and the electronic channels are located on two opposing edges.

[0014] In one embodiment, in the first direction, the flash evaporator is separated from the electronic channel.

[0015] In summary, the present invention has the following beneficial effects: the aerosol thermal desorption ion source includes a flash evaporator with a cuboid structure. By limiting the cross-sectional shape of the flash evaporator, the gas generated by heating and vaporizing the flash evaporator can be made to be close to the cross-sectional shape of the flash evaporator, thereby increasing the overlap between the gas distribution area and the transmission area of ​​the directional electron beam and improving the ionization efficiency of gas molecules. Attached Figure Description

[0016] Figure 1 A schematic diagram of the three-dimensional structure of an existing aerosol thermal desorption ion source.

[0017] Figure 2 This is a schematic cross-sectional view of the internal structure of an existing aerosol thermal desorption ion source.

[0018] Figure 3 for Figure 2 Enlarged diagram of part A in the diagram;

[0019] Figure 4 This is a three-dimensional structural diagram of the flash evaporator portion of the aerosol thermal desorption ion source according to an embodiment of this application.

[0020] Figure 5 This is a three-dimensional structural diagram of the flash evaporator according to an embodiment of this application;

[0021] Figure 6 This is a schematic cross-sectional view of the internal structure of the flash evaporator in an embodiment of this application;

[0022] Figure 7 for Figure 6 Enlarged diagram of part B in the diagram;

[0023] Figure 8 This is a cross-sectional schematic diagram of the internal structure of the flash evaporator according to an embodiment of this application.

[0024] Figure 9 This is a schematic diagram simulating a cuboid flash evaporator of a first size according to an embodiment of this application;

[0025] Figure 10 This is a schematic diagram of a cuboid flash evaporator of a second size according to an embodiment of this application.

[0026] Figure 11 This is a schematic diagram of a cuboid flash evaporator of a third size according to an embodiment of this application;

[0027] Figure 12 This is a schematic diagram of a cuboid flash evaporator of a fourth size according to an embodiment of this application.

[0028] Figure 13 This is a schematic diagram of a cuboid flash evaporator of the fifth size according to an embodiment of this application;

[0029] Figure 14 This is a schematic diagram of a cuboid flash evaporator of the sixth size according to an embodiment of this application;

[0030] Figure 15 This is a simulated schematic diagram of a cuboid flash evaporator of the seventh size according to an embodiment of this application.

[0031] Figure 16 This is a schematic diagram of a cuboid flash evaporator of the eighth size according to an embodiment of this application.

[0032] Figure 17 This is a schematic diagram of a cuboid flash evaporator of the ninth size according to an embodiment of this application;

[0033] Figure 18 This is a simulation diagram of ion transport in an existing aerosol thermal desorption ion source.

[0034] Figure 19 This is a simulation diagram of ion transport in the aerosol thermal desorption ion source of Embodiment 1 of this application;

[0035] Figure 20 This is a schematic diagram of the groove opening of a cuboid flash evaporator.

[0036] In the diagram: 1. Flash evaporator; 11. Groove; 12. Limiting groove; 2. Filament; 3. Guiding focusing module; 4. Time-of-flight mass spectrometry module; 5. Gas gathering hood; 51. Electronic channel. Detailed Implementation

[0037] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0038] In this invention, unless otherwise expressly specified and limited, "above" or "below" a second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of a second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" of a second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature. The terms "vertical," "horizontal," "left," "right," "above," "below," and similar expressions are for illustrative purposes only and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0040] Example 1

[0041] To address the aforementioned issues, the overall function of the aerosol thermal desorption ion source will first be explained. For example... Figure 1 As shown, in order to facilitate the description of the device of this application, the various directions are first defined, wherein the first direction is the X1X2 direction, the second direction is the Y1Y2 direction, and the third direction is the Z1Z2 direction. Aerosols enter the vacuum through an aerodynamic lens and are focused into a particle beam. The particle beam is approximately linearly aligned and impacts a flash evaporator along the X2 direction. The cylindrical flash evaporator has a conical groove on its top surface. Heated by resistance wires, the flash evaporator is maintained at a high temperature of 600℃~800℃. Upon impact with the groove, the particle beam is vaporized by the high temperature of the flash evaporator, causing the volatile components in the particles to evaporate and generate the gas sample to be detected. In the third direction, Z1Z2, a filament (specifically a tungsten filament) is located on each side of the flash evaporator. Heated to a high temperature, this filament generates an electron beam. This electron beam collides with the gas molecules produced by pyrolysis, generating positive ions. The electrons emitted by the filaments bombard the gas molecules, producing fragment ions. These fragment ions are transported along the Y2 direction and focused into an ion beam by a guiding focusing module 3. Finally, the ion beam enters the time-of-flight mass spectrometry module 4 for analysis to obtain the mass spectrometry results.

[0042] like Figure 2 , Figure 3As shown, in the above technical solution, the flash evaporator is not merely a heating element; its geometry determines the spatial distribution shape of the pyrolysis gas, thus directly affecting the degree of spatial overlap between the gas and the electron beam. Traditional cylindrical flash evaporators, due to their curved structure, result in a ring-shaped gas distribution after pyrolysis, while the electron beams emitted from the filaments on both sides are mostly parallel rectangular in shape. This makes it difficult for the two to fully overlap, thus limiting ionization efficiency.

[0043] To address the aforementioned shortcomings, this embodiment provides a novel aerosol thermal desorption ion source, specifically involving modifications to the structure of the flash evaporator 1, such as... Figure 5 As shown, the flash evaporator 1 is generally rectangular in shape, having a length L along a first direction, a width W along a second direction, and a thickness D along a third direction; and when viewed along the first direction, the cross-section of the flash evaporator 1 is rectangular. Furthermore, by controlling the width of the rectangular flash evaporator 1 in the second direction, the gas produced by the flash evaporator 1 can be fully covered by the parallel rectangular electron beams generated by the filaments 2 on both sides, thereby allowing electrons to fully collide with gas molecules and improving the ionization efficiency of gas molecules.

[0044] The flash evaporator 1 has a first end and a second end arranged opposite to each other along the direction of particle beam transport. That is, the flash evaporator 1 has a first end near the X1 direction and a second end near the X2 direction. The end that collides with the particles in the particle beam is the first end. To avoid the phenomenon of particles bouncing back after colliding with the end face of the flash evaporator 1, which would prevent the particles from being fully heated, the flash evaporator 1 has a groove 11 at the first end. The groove 11 extends from the first end of the flash evaporator 1 into the interior of the flash evaporator 1, forming a height difference in the first direction. After the particle beam collides with the groove 11, it can remain in the groove 11 and achieve complete heating and vaporization. By opening the groove 11 at the first end of the flash evaporator 1, the particle retention capacity can be effectively improved, thereby enabling the particles to be fully vaporized.

[0045] like Figure 20 As shown, in some embodiments, the shape of the groove 11 can be a U-shaped groove, a V-shaped groove, or a groove 11 of other shapes.

[0046] like Figure 18 , Figure 19 The image shows a comparison of simulation results before and after replacing flash evaporator 1. Figure 18 A cylindrical flash evaporator 1 was used, with a cross-sectional dimension of 4mm × 4mm. The ion transport simulation result was 2.8mm. Figure 19A cuboid flash evaporator 1 was used, with a cross-sectional dimension of 1.5mm × 4mm. The simulated ion transport result was 1.3mm. Based on the above, it can be seen that by changing the shape of the flash evaporator 1, the divergence of the ion beam can be effectively suppressed, thus enhancing the ion focusing performance.

[0047] The cuboid flash evaporator 1 provides a larger plane for the electron beam to interact, reducing geometric obstruction and allowing the electron beam to penetrate and fully cover the pyrolysis region. Because the neutral gas generated by pyrolysis is more concentrated at the geometric center, the spatial overlap volume between the electron beam and gas molecules increases, ensuring the ion cloud is within the entire electron coverage area. This increases the probability of effective electron-molecule collisions, significantly improving the ion generation rate per unit time and enhancing the ionization efficiency (IE). Secondly, by designing the flash evaporator 1 as a cuboid, this embodiment creates a narrower, flatter gas flow distribution as the gas exits the flash evaporator 1 after pyrolysis. In time-of-flight mass spectrometry, the initial beam width of ions in the acceleration region directly affects the differences in flight paths and the dispersion of arrival times. A smaller beam width helps reduce the broadening of ion flight time, thereby improving mass spectrometry resolution. Simulation results show that the structure of this invention significantly reduces the longitudinal beam width of the ion beam in the acceleration region to approximately 0.3 mm, effectively suppressing ion beam divergence, enhancing ion focusing performance, and improving the instrument's mass resolution and detection sensitivity. This optimization is particularly crucial for the separation and identification of complex aerosol components.

[0048] To further improve the particle retention capacity of the flash evaporator 1, the groove 11 in this embodiment is approximately rectangular in shape, with a flat bottom surface. The bottom surface of the groove 11 intersects at least the first direction; in some embodiments, the bottom surface of the groove 11 is perpendicular to the first direction. A limiting groove 12 is further formed on the bottom surface of the groove 11. While a smooth, flat bottom surface has a relatively high probability of particle reflection after collision, the limiting groove 12 increases the surface roughness, thus greatly increasing the probability of particles remaining on the bottom surface and further promoting complete vaporization of the particles.

[0049] like Figure 5 , Figure 7 As shown, in some embodiments, the limiting groove 12 can adopt a pyramidal structure. The side surface of the pyramid absorbs the kinetic energy of the particles through mutual friction, thereby reducing the rebound effect of the particles. In some embodiments, in order to increase the arrangement density of the limiting groove 12, the limiting groove 12 specifically adopts a regular square pyramidal structure, such as... Figure 8 As shown, the limiting groove 12 has a first included angle A1 between two opposite sides; the angle of the first included angle A1 is between 0° and 90°.

[0050] In some embodiments, the flash evaporator 1 is made of porous tungsten material. The porous tungsten structure retains its intrinsic thermal and mechanical properties while further possessing the advantages of high specific surface area and good gas permeability. The larger specific surface area helps enhance the contact and heat transfer of aerosol particles on the high-temperature surface, improving the evaporation and pyrolysis efficiency of the particles; simultaneously, the microchannels in the porous structure can effectively promote the release of neutral molecules after evaporation, reducing the interference of local gas accumulation on the temperature field and maintaining the thermal stability of the heating region.

[0051] Example 2

[0052] In some embodiments, when viewed from the first direction, the cross-sectional dimensions of the conventional cylindrical flash evaporator 1 are specifically 4mm*4mm. To accommodate the ion source of the cylindrical flash evaporator 1, this application further defines the dimensions of the cuboid flash evaporator 1, such as... Figure 5 As shown, the width W of the flash evaporator 1 in the second direction satisfies: 0.5mm < W < 2mm; the thickness D of the flash evaporator 1 in the third direction satisfies: 2mm < D < 4mm. That is, when viewed along the first direction, the flash evaporator 1 of this application is a long, narrow rectangle, relatively narrow in the second direction, but relatively wide in the third direction. This size allows the gas generated by the flash evaporator 1 to be completely within the coverage of the electron beam in the second direction. Simultaneously, in the third direction, the flash evaporator 1 can be completely positioned between the two filaments 2, ensuring that gas molecules can fully collide with the electron beam. By defining the shape and size of the flash evaporator 1, the flat gas flow pattern under the cuboid structure makes the ion generation position more concentrated in the second direction. A smaller beam width helps reduce the broadening of ion flight time, effectively suppressing ion beam divergence and enhancing ion focusing performance.

[0053] Furthermore, to illustrate the preferred size range of flash evaporator 1, this application also provides some simulation results, such as... Figures 9-17 The figure shows simulation results of various cuboid flash evaporators 1 with different sizes. Among them, the width W in the second direction and the thickness D in the third direction of the flash evaporator 1 are of particular interest. This is because the width W in the second direction determines whether the electron beam can cover the gas range, and the thickness D in the third direction determines the initial width of the ion beam.

[0054] Combination Figures 9-13 As can be seen from the content, when the thickness D remains constant and the width W gradually increases, the bundle width will increase with the increase of the width W.

[0055] Combination Figures 13-15 as well as Figure 17 It can be seen that when the width W remains constant and the thickness D gradually increases, the beam width will gradually increase with the increase of the thickness D.

[0056] Based on the final simulation results, it can be seen that if the beam width after focusing needs to be controlled within 2mm, the width W of the flash evaporator 1 in the second direction satisfies: W < 2mm; the thickness D of the flash evaporator 1 in the third direction satisfies: D < 4mm; at the same time, in order to avoid the flash evaporator 1 being too small, which would cause the particles to not accurately impact the flash evaporator 1, it is also necessary to limit the minimum size of the flash evaporator 1. In this embodiment, the preferred size of the flash evaporator 1 is: 0.5mm < W < 2mm, 2mm < D < 4mm.

[0057] Example 3

[0058] In some embodiments, such as Figure 4 , Figure 6 , Figure 7 As shown, it also includes: a gas gathering hood 5, which has a cylindrical structure and whose axis is parallel to the first direction; the gas gathering hood 5 is arranged around the flash evaporator; the gas gathering hood 5 can gather the gas generated by the flash evaporator inside it so that the gas can be fully ionized.

[0059] In the third direction, the gas gathering hood 5 has electron channels 51 opposite to it; electrons released by the filament can enter the interior of the gas gathering hood 5 through the electron channels 51. The gas gathering hood 5 is hexagonal prism-shaped, and the electron channels 51 are located on two opposite edges. Specifically, placing the electron channels 51 on two opposite edges allows the electron channels 51 to be closer to the filament, thereby increasing the diffusion range of the electron beam and preventing the gas gathering hood 5 from affecting the transmission of the electron beam. In the gas gathering area, the hexagonal prism-shaped gas gathering hood 5 specifically consists of two parallel plates in the second direction, which keeps the edges of the gas parallel to each other in the second direction, thereby allowing gas molecules to collide with electrons as much as possible.

[0060] like Figure 7 As shown, in the first direction, the flash evaporator and the electron channel are separated, meaning the electron channel is completely above the flash evaporator. This allows gas molecules generated by particles impacting the flash evaporator's recesses to be ionized by the electron beam emitted by the filament as much as possible after escaping into space through the recess openings. In some embodiments, the width of the electron channel in the second direction is greater than the width of the flash evaporator to ensure the electron beam completely covers the gas.

[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. Aerosol thermal desorption ion source, including: A flash evaporator is used to receive a particle bundle transported in a first direction and to heat and vaporize the particles in the particle bundle to generate gas molecules. The filament is used to release electrons to ionize gas molecules and generate ions; Its features are, The flash evaporator has a length along a first direction, a width along a second direction, and a thickness along a third direction; the first direction, the second direction, and the third direction intersect each other; In the first direction, the cross section of the flash evaporator perpendicular to the first direction is rectangular; the flash evaporator is provided with a first end and a second end in sequence along the particle beam transmission direction; a groove for accommodating particles is provided at the first end, and the groove extends into the interior of the flash evaporator along the first direction; In the second direction, the width of the flash evaporator is smaller than the irradiation range of the filament; In the third direction, the filaments are arranged on both sides of the flash evaporator.

2. The aerosol thermal desorption ion source according to claim 1, characterized in that, The bottom surface of the groove intersects with the first direction; the bottom surface of the groove is provided with a plurality of limiting grooves for reducing particle reflection.

3. The aerosol thermal desorption ion source according to claim 2, characterized in that, The limiting groove has a pyramidal structure; the width of the limiting groove gradually decreases along the transmission direction of the particle beam.

4. The aerosol thermal desorption ion source according to claim 3, characterized in that, The limiting groove has a regular square pyramid structure, and there is a first included angle A1 between two opposite sides of the limiting groove; the angle of the first included angle A1 is between 0° and 90°.

5. The aerosol thermal desorption ion source according to claim 4, characterized in that, The width W of the flash evaporator in the second direction satisfies: 0.5mm < W < 2mm; the thickness D of the flash evaporator in the third direction satisfies: 2mm < D < 4mm.

6. The aerosol thermal desorption ion source according to any one of claims 1-5, characterized in that, The flash evaporator is made of porous tungsten material.

7. The aerosol thermal desorption ion source according to claim 1, characterized in that, It also includes: a gas gathering hood, which has a cylindrical structure and whose axis is parallel to the first direction; The gas gathering hood is arranged around the flash evaporator; In the third direction, the gas gathering hood is provided with an electronic channel; electrons released by the filament can enter the interior of the gas gathering hood through the electronic channel.

8. The aerosol thermal desorption ion source according to claim 7, characterized in that, The gas gathering hood is hexagonal prism-shaped, and the electron channels are located on two opposite edges.

9. The aerosol thermal desorption ion source according to claim 7, characterized in that, In the first direction, the flash evaporator is separated from the electronic channel.

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