Gas chromatography-low temperature plasma-ion mobility spectrometry combined device

Abstract

The invention relates to the technical field of analytical chemistry detection, in particular to a gas chromatography-low temperature plasma-ion mobility spectrometry combined device. The device comprises a gas chromatography unit, a low-temperature plasma ionization source and an ion migration tube. The gas chromatography unit comprises an inlet capillary tube, a capillary column and an outlet capillary tube which are communicated in sequence; an L-shaped air channel and a discharge area are arranged in an insulation base of the low-temperature plasma ionization source, one end of the L-shaped air channel is communicated with an outlet capillary tube, the other end of the L-shaped air channel is communicated with the discharge area, an insulation medium tube is coaxially installed in the discharge area, an inner electrode is arranged along the axis of the insulation medium tube and penetrates through the insulation base, and an outer electrode wraps the insulation medium tube. The high-voltage power supply is electrically connected with the two electrodes; the ion migration tube body is provided with a repulsion electrode, an ion gate, a Faraday disc and an air port, and an ion channel of the repulsion electrode is communicated with the discharge area. The device realizes efficient combination and improves the detection performance.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry detection technology, and in particular to a gas chromatography-low-temperature plasma-ion mobility spectrometry (GC-ALPS) coupled device. Background Technology

[0002] Gas chromatography-ion mobility spectrometry (GC-IMS) combines the high separation efficiency of gas chromatography with the high sensitivity, rapid response, and portability of IMS, making it an important tool for the analysis of trace volatile organic compounds (VOCs) in fields such as environmental monitoring, food safety, public safety, and medical diagnostics. However, the overall performance of this technology is largely limited by the efficiency of its core component—the ionization source—and the design of its interface.

[0003] Currently, GC-IMS technology mainly faces the following challenges: 1. Inherent limitations of traditional ionization sources: IMS traditionally uses radioactive ionization sources (such as...) 6 While Ni (³Ni) exhibits good stability, it suffers from strict regulation, low safety, and poor public acceptance. Non-radioactive alternative sources, such as corona discharge, often struggle to produce pure and controllable reagent ions when using air as the working gas, leading to complex background signals and uncontrollable ionization processes, thus affecting detection selectivity and sensitivity. Ultraviolet lamp ionization sources, limited by their finite photoionization energy, are insufficiently efficient at ionizing many compounds, severely restricting detection sensitivity.

[0004] 2. Sample Dilution and Peak Broadening at the Interface: In conventional GC-IMS interface designs, gaseous samples separated by the capillary column are often directly exposed to the atmospheric environment of the ionization zone of the ion migration tube during effluent flow. This process causes the sample to be severely diluted by the carrier gas due to volume expansion, resulting in broadening of the chromatographic separation peaks and a sharp drop in the effective sample concentration. This dilution effect directly reduces the number of sample molecules participating in ionization, becoming a key bottleneck restricting the improvement of detection sensitivity.

[0005] Low-temperature plasma ionization (LTP) sources, as a highly efficient atmospheric pressure soft ionization technology, have attracted much attention due to their advantages such as high ionization efficiency, no need for complex pretreatment, generation of abundant reactive ions, and easy control of selectivity through doping gases. Among existing technologies, patent CN101946300A provides a universal LTP probe; patents CN109545648B and CN104713941B explore the combination or switching modes of LTP with other ionization sources (such as electrospray and nickel sources) to expand the compound detection range in mass spectrometry; and patent CN120072620A directly uses LTP as an ionization source for IMS, demonstrating its flexibility in controlling reactive reagent ions through an array electrode and multi-gas interface design.

[0006] However, directly applying general LTP technology to GC-IMS systems still faces significant challenges. The core issue is that existing solutions fail to effectively address the diffusion and dilution problems during sample transport from the column outlet to the LTP discharge region, and also lack a dedicated interface design that is highly efficient and integrated to suit the characteristics of GC-IMS systems.

[0007] Patent CN109682906B provides a device for combining gas chromatography with a low-temperature plasma ion source and mass spectrometer. This device directly introduces GC eluent into the LTP discharge region and then into the mass spectrometer via an insulating chamber and insulating dielectric tube, effectively suppressing sample diffusion. However, this device is specifically designed for mass spectrometers, and its core structure (such as the insulating dielectric tube) primarily serves the specific requirement of adapting to the high-vacuum sample introduction interface of the mass spectrometer. Ion mobility spectrometry (IMS) operates at atmospheric pressure and does not have a vacuum interface issue. Directly applying this MS-guided structure is not only suboptimal but may also fail to fully utilize the technical characteristics of IMS.

[0008] In summary, although low-temperature plasma technology itself is relatively mature, how to innovatively integrate it with the GC-IMS system and design an interface device specifically for this combined technology to simultaneously solve key issues such as sample dilution, low ionization efficiency, and stable operation of the ionization source remains a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0009] In view of this, the present invention provides a gas chromatography-low temperature plasma-ion mobility spectrometry coupled device.

[0010] Therefore, the present invention provides the following technical solution: A gas chromatography-low-temperature plasma-ion mobility spectrometry (GC-PLAS) device includes a gas chromatography unit, a low-temperature plasma ionization source, and an ion mobility tube. The gas chromatography unit includes an inlet capillary, a capillary column, and an outlet capillary. The outlet end of the inlet capillary is connected to the inlet end of the capillary column, and the outlet end of the capillary column is connected to the inlet end of the outlet capillary. The low-temperature plasma ionization source includes an insulating base, a discharge gas inlet pipe, an inner electrode, an outer electrode, an insulating dielectric tube, and a high-voltage power supply. The insulating base contains an L-shaped gas channel and a discharge region. One end of the L-shaped gas channel is a sample inlet connected to the outlet end of the outlet capillary, and the other end is connected to the discharge region. The insulating base has a discharge gas inlet, the inlet end of which is connected to the discharge gas inlet pipe. The insulating dielectric tube is coaxially mounted within the discharge region. The inner electrode is arranged along the central axis of the insulating dielectric tube, passing sequentially through the horizontal section of the L-shaped gas channel and the insulating base. The outer electrode is located within the discharge region and covers the outside of the insulating dielectric tube. The high-voltage power supply is electrically connected to both the inner and outer electrodes. The ion migration tube includes an ion migration tube body, a repulsion electrode, an ion gate, and a Faraday disk arranged sequentially on the ion migration tube body along the ion migration direction, and a migration tube outlet and a drift gas inlet arranged sequentially on the side wall of the ion migration tube body in the opposite direction to the ion migration direction; the repulsion electrode is located at one end of the ion migration tube body near the discharge region of the low-temperature plasma ionization source, and the ion channel of the repulsion electrode is connected to the outlet end of the discharge region.

[0011] Furthermore, the discharge gas inlet pipe and outlet capillary are respectively connected to the corresponding discharge gas inlet and sample inlet through gas connectors.

[0012] Furthermore, a cooling cavity is provided on the insulating base corresponding to the position of the external electrode, and a cooling gas inlet and a cooling gas outlet are respectively connected to the cooling cavity on the insulating base.

[0013] Furthermore, the L-shaped gas channel includes a vertical section and a horizontal section. The horizontal section is connected to the discharge area. The sample inlet and the discharge gas inlet are both located in the area corresponding to the vertical section of the insulating base and are connected to the vertical section of the L-shaped gas channel. The aperture range of the vertical section of the L-shaped gas channel is 0.5–2 mm.

[0014] Furthermore, the insulating base is made of polytetrafluoroethylene, polyetheretherketone, or ceramic; the insulating dielectric tube is made of quartz or alumina ceramic; the inner electrode is made of tungsten or stainless steel, and has a rod-shaped, needle-shaped, or rod-shaped at one end and spiral-shaped at the other end; the outer electrode is a metal tube, metal mesh, or metal foil structure, and the outer electrode is tightly attached to the outer wall of the insulating dielectric tube.

[0015] Furthermore, the ion migration tube is a migration time ion migration tube, a traveling wave ion migration tube, a trap ion migration tube, or an asymmetric field ion migration tube.

[0016] Furthermore, a grid is installed inside the ion migration tube body between the ion gate and the Faraday disk.

[0017] Furthermore, the low-temperature plasma ionization source also includes a preheating device, which is installed on the pipeline of the discharge gas inlet pipe.

[0018] Advantages and positive effects of the present invention: The advantages of this invention lie in its design of a highly efficient interface and a stable ionization structure, with significant advantages including: Significantly enhanced detection sensitivity: By directly guiding the elution outlet of the gas chromatography unit's outlet capillary to or placing it within or adjacent to the discharge region of the low-temperature plasma ionization source, "in-situ" or "near-in-situ" ionization of the chromatographic effluent with high-density plasma active particles is achieved. This design maximizes the high ionization efficiency of the low-temperature plasma, ensuring that sample molecules are efficiently ionized before being severely diluted, thereby significantly improving the ion yield and detection sensitivity of the ion migration tube.

[0019] Effectively reducing sample diffusion and dilution: This invention provides a confined space for the interaction between gas chromatography eluent and low-temperature plasma (LTP) by optimizing the insertion depth of the outlet capillary and the microporous cavity design of the L-shaped gas channel. This design significantly reduces the diffusion and dilution effects of sample components released into the atmosphere at the capillary column outlet, maintaining high resolution of chromatographic separation and ensuring that high concentrations of sample molecules enter the ionization process, fundamentally improving ionization efficiency.

[0020] Effectively reduces sample residue: This invention preheats the discharge gas in advance using a preheating device, so that the analytes eluted from the chromatography do not deposit due to cold, thereby effectively reducing the sample residue of the ionized portion in the low-temperature plasma ionization source.

[0021] Improving Ionization Source Stability: While the plasma temperature is lower during operation of a low-temperature plasma ionization source due to the reduced charge carrier and discharge intensity (compared to corona and glow discharge), the ionization source itself still generates a significant amount of heat, leading to a temperature increase and consequently reducing discharge performance. This invention addresses this by providing a dedicated cooling chamber on the insulating base corresponding to the external electrode position, and by introducing cooling gas or coolant through cooling gas inlets and outlets, maintaining the ionization source's low-temperature operating state and ensuring its stability.

[0022] Flexible gas supply and reaction control: This invention features a dedicated discharge gas channel via a discharge gas inlet pipe and a discharge gas outlet, enabling highly flexible discharge gas supply. The low-temperature plasma ionization source can directly utilize the carrier gas from the gas chromatography unit (such as nitrogen, argon, hydrogen, or mixtures thereof) as the discharge gas. Alternatively, it can supplement or switch to different discharge gases (such as pure air, specific inert gases) or chemically doped reagent gases (such as acetone, toluene, dichloromethane vapor, etc.) via independent gas path interfaces as needed. This design allows for precise control of the composition of the reagent ions and the ionization chemical environment, thereby enhancing the ionization selectivity and specificity for specific target compounds and facilitating the qualitative analysis of trace substances in complex matrices.

[0023] In summary, this invention, through innovative structural design, seamlessly integrates the high-efficiency separation of gas chromatography, the high-efficiency and controllable ionization of low-temperature plasma, and the rapid separation and detection of ion mobility spectrometry (IMS). It effectively solves the key problems of sample dilution, low ionization efficiency, sample residue, and poor ionization source stability in traditional GC-IMS coupling, and achieves a significant improvement in the detection sensitivity, selectivity, and stability of the device. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a gas chromatography-low-temperature plasma-ion mobility spectrometry (GC-ALPS) device provided by the present invention.

[0026] In the diagram: 1. Discharge gas inlet pipe; 2. Preheating device; 3. Gas passage; 4. Inner electrode; 5. Insulating base; 6. Discharge gas inlet; 7. Sample inlet; 8. Insulating dielectric tube; 9. Outer electrode; 10. High voltage power supply; 11. Cooling chamber; 12. Cooling gas inlet; 13. Cooling gas outlet; 14. Discharge area; 15. Repulsion electrode; 16. Migration tube outlet; 17. Ion gate; 18. Grid; 19. Faraday disk; 20. Drift gas inlet; 21. Gas connector; 22. Outlet capillary; 23. Capillary column; 24. Inlet capillary. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0028] This invention provides a gas chromatography-low-temperature plasma-ion mobility spectrometry (GC-ALPS) coupled device, such as... Figure 1 As shown, it includes a gas chromatography unit, a low-temperature plasma ionization source, and an ion migration tube.

[0029] The gas chromatography unit includes an inlet capillary 24, a capillary column 23, and an outlet capillary 22. The outlet end of the inlet capillary 24 is connected to the inlet end of the capillary column 23, and the outlet end of the capillary column 23 is connected to the inlet end of the outlet capillary 22.

[0030] The low-temperature plasma ionization source includes an insulating base 5, a discharge gas inlet pipe 1, a preheating device 2, an inner electrode 4, an outer electrode 9, an insulating dielectric tube 8, and a high-voltage power supply 10. The insulating base 5 is provided with an L-shaped gas channel 3 and a discharge region 14. The L-shaped gas channel 3 includes a vertical section and a horizontal section that are interconnected. The inlet of the vertical section is a sample inlet 7, which is connected to the outlet end of the outlet capillary 22 through a gas connector 21. The horizontal section is connected to the discharge region 14. A discharge gas inlet 6 is provided on the insulating base 5 in the region corresponding to the vertical section. The discharge gas inlet 6 is connected to the vertical section of the L-shaped gas channel 3. The aperture range of the vertical section of the L-shaped gas channel 3 is 0.5–2 mm.

[0031] The inlet end of the discharge gas inlet 6 is connected to the discharge gas inlet pipe 1 via a gas connector 21. The preheating device 2 is installed on the discharge gas inlet pipe 1. The insulating dielectric tube 8 is coaxially installed in the discharge area 14. The inner electrode 4 is arranged along the central axis of the insulating dielectric tube 8, passing through the horizontal section of the L-shaped gas channel 3 and the insulating base 5 in sequence. The outer electrode 9 is located in the discharge area 14 and covers the outside of the insulating dielectric tube 8. The high-voltage power supply 10 is electrically connected to the inner electrode 4 and the outer electrode 9. A cooling chamber 11 is provided on the insulating base 5 at the position corresponding to the outer electrode 9. A cooling gas inlet 12 and a cooling gas outlet 13, which are respectively connected to the cooling chamber 11, are provided on the insulating base 5.

[0032] The ion migration tube includes an ion migration tube body, a repulsion electrode 15, an ion gate 17, a grid 18 and a Faraday disk 19 arranged sequentially on the ion migration tube body along the ion migration direction, and a migration tube outlet 16 and a drift gas inlet 20 arranged sequentially on the side wall of the ion migration tube body in the opposite direction to the ion migration direction; the repulsion electrode 15 is located at one end of the ion migration tube body near the discharge region 14 of the low-temperature plasma ionization source, and the ion channel of the repulsion electrode 15 is connected to the outlet end of the discharge region 14.

[0033] The insulating base 5 is made of polytetrafluoroethylene, polyetheretherketone, or ceramic; the insulating dielectric tube 8 is made of quartz or alumina ceramic; the inner electrode 4 is made of tungsten or stainless steel, and its structure is rod-shaped, needle-shaped, or rod-shaped at one end and spiral-shaped at the other end; the outer electrode 9 is a metal tube, metal mesh, or metal foil structure, and the outer electrode 9 is tightly attached to the outer wall of the insulating dielectric tube 8.

[0034] Ion migration tubes can be migration-time ion migration tubes, traveling-wave ion migration tubes, trap ion migration tubes, or asymmetric field ion migration tubes.

[0035] Working principle: A carrier gas (such as nitrogen, helium, hydrogen, or air) carries the sample to be detected from the inlet capillary 24 into the capillary column 23 of the gas chromatography unit. The gas chromatography unit has heating and temperature control functions and can operate in isothermal or programmed temperature mode, adaptable to analytes with different boiling point ranges. Within the capillary column 23, the sample is efficiently separated along the column length based on the differences in the partition coefficients of each component. The separated analyte components flow out sequentially through the outlet capillary 22 in order of boiling point or polarity. The outlet capillary 22 is sealed to the injection port 7 of the low-temperature plasma ionization source via a gas connector 21, and its insertion depth can be adjusted to extend into the L-shaped gas channel 3, minimizing sample diffusion and dead volume.

[0036] The discharge gas (which can be the gas chromatograph carrier gas directly, or can be switched to pure air, specific inert gas, and chemical doping reagent gas as needed) is transported through the discharge gas inlet pipe 1. Before entering the ionization source, it is preheated by the preheating device 2. The preheating temperature is not lower than the working temperature of the gas chromatograph unit to avoid the analyte from being adsorbed by cold or producing a memory effect.

[0037] The preheated discharge gas is introduced into the discharge gas inlet 6 through the gas connector 21, and is thoroughly mixed with the analyte flowing out from the outlet capillary 22 in the vertical section of the L-shaped gas channel 3. The microporous design (pore size range 0.5–2 mm) of the L-shaped gas channel 3 further suppresses sample diffusion and ensures that the high-concentration mixed gas is delivered to the discharge region 14 through the horizontal section.

[0038] A high-frequency, high-voltage electric field is applied to the inner electrode 4 and the outer electrode 9 by a high-voltage power supply 10. Since the two electrodes are located inside and outside the insulating dielectric tube 8 respectively and are arranged coaxially, the discharge gas in the discharge region 14 is excited to form a low-temperature plasma under the action of the electric field. The analytes in the mixed gas react with active particles such as electrons, ions, and excited-state species in the plasma to achieve efficient "in-situ" or "near-in-situ" ionization and generate target ions.

[0039] Cooling gas (or coolant) is introduced into the cooling chamber 11 through the cooling gas inlet 12 and discharged through the cooling gas outlet 13, continuously carrying away the heat generated during ionization, maintaining the low-temperature working state of the ionization source, avoiding heat accumulation that leads to a decrease in discharge performance, and ensuring ionization stability.

[0040] The target ions generated in the discharge region 14 enter the ion migration tube body through the ion channel of the repulsion electrode 15 under the action of the gas flow and electric field. The repulsion electrode 15 is located at one end of the ion migration tube body near the discharge region 14, and its ion channel is connected to the outlet end of the discharge region 14 to ensure efficient ion introduction.

[0041] A drift gas (such as pure air or nitrogen) is introduced into the ion migration tube body through the drift gas inlet 20, forming a stable airflow environment. The ion gate 17 opens periodically according to a preset sequence, allowing discrete ion beams to enter the migration zone. Different types of ions undergo secondary separation within the migration zone due to differences in mobility, under the influence of the drift gas flow and electric field. They then pass sequentially through the grid 18 (aiding ion focusing and transport) and finally reach the Faraday disk 19. The Faraday disk 19 converts the ion signal into an electrical signal and outputs it. After subsequent data processing, an ion migration spectrum is obtained, enabling qualitative and quantitative detection of the analyte. The detected waste gas is discharged through the migration tube outlet 16.

[0042] Throughout the entire workflow, each unit achieves seamless integration from analyte separation and ionization to detection through optimized interface design and structural matching. This effectively solves problems such as sample dilution, low ionization efficiency, and severe residue in traditional coupled devices, while taking into account separation resolution, detection sensitivity, and long-term operational stability.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gas chromatography - low temperature plasma - ion mobility spectrometry combination apparatus, characterized by, The gas chromatograph unit, the low-temperature plasma ionization source and the ion migration tube are combined. The gas chromatograph unit comprises an inlet capillary (24), a capillary column (23) and an outlet capillary (22), the outlet end of the inlet capillary (24) is communicated with the inlet end of the capillary column (23), and the outlet end of the capillary column (23) is communicated with the inlet end of the outlet capillary (22). The low-temperature plasma ionization source comprises an insulating base (5), a discharge gas inlet pipe (1), an inner electrode (4), an outer electrode (9), an insulating medium pipe (8) and a high-voltage power supply (10), the insulating base (5) is internally provided with an L-shaped gas channel (3) and a discharge area (14), one end of the L-shaped gas channel (3) is a sample inlet (7) and is communicated with the outlet end of the outlet capillary (22), and the other end is communicated to the discharge area (14); the insulating base (5) is provided with a discharge gas inlet (6), the inlet end of the discharge gas inlet (6) is communicated with the discharge gas inlet pipe (1); the insulating medium pipe (8) is coaxially installed in the discharge area (14), the inner electrode (4) is arranged along the central axis of the insulating medium pipe (8) and sequentially passes through the horizontal section of the L-shaped gas channel (3) and the insulating base (5); the outer electrode (9) is located in the discharge area (14) and is coated outside the insulating medium pipe (8); the high-voltage power supply (10) is electrically connected with the inner electrode (4) and the outer electrode (9). The ion migration tube comprises an ion migration tube body, repulsion electrodes (15), an ion gate (17) and a Faraday disc (19) which are sequentially arranged on the ion migration tube body along the ion migration direction, and a migration tube gas outlet (16) and a drift gas inlet (20) which are sequentially arranged on the side wall of the ion migration tube body along the direction opposite to the ion migration direction; the repulsion electrodes (15) are arranged at one end of the ion migration tube body close to the discharge area (14) of the low-temperature plasma ionization source, and the ion channel of the repulsion electrodes (15) is communicated with the outlet end of the discharge area (14).

2. The apparatus according to claim 1, wherein the low temperature plasma is generated by a microwave plasma source. The discharge gas inlet pipe (1) and the outlet capillary (22) are respectively communicated with the corresponding discharge gas inlet (6) and sample inlet (7) through gas joints (21).

3. The apparatus according to claim 1, wherein the low temperature plasma is generated by a microwave plasma source. The insulating base (5) is provided with a cooling cavity (11) at the position corresponding to the outer electrode (9), and the insulating base (5) is provided with a cooling gas inlet (12) and a cooling gas outlet (13) which are respectively communicated with the cooling cavity (11).

4. The apparatus according to claim 1, wherein the low temperature plasma is generated by a microwave plasma source. The L-shaped gas channel (3) comprises a vertical section and a horizontal section, the horizontal section is communicated with the discharge area (14), the sample inlet (7) and the discharge gas inlet (6) are arranged in the region of the insulating base (5) corresponding to the vertical section and are communicated with the vertical section of the L-shaped gas channel (3); the aperture of the vertical section of the L-shaped gas channel (3) ranges from 0.5 mm to 2 mm.

5. The apparatus according to claim 1, wherein the low temperature plasma is generated by a microwave plasma source. The insulating base (5) is made of polytetrafluoroethylene, polyether ether ketone or ceramic; the insulating medium tube (8) is made of quartz or alumina ceramic; the inner electrode (4) is made of tungsten or stainless steel and has a rod-like, needle-like or rod-like at one end and spiral-like at the other end structure; the outer electrode (9) has a metal tube, metal mesh or metal foil structure and is tightly attached to the outer wall of the insulating medium tube (8).

6. The apparatus according to claim 1, wherein the low temperature plasma is generated by a microwave plasma source. The ion migration tube is a migration time ion migration tube, a traveling wave ion migration tube, a trap ion migration tube or an asymmetric field ion migration tube.

7. The apparatus according to claim 1, wherein the low temperature plasma is generated by a microwave plasma source. A grid (18) is installed between the ion gate (17) and the Faraday disc (19) in the ion migration tube body.

8. The apparatus according to claim 1, wherein the apparatus is a gas chromatography-cryogenic plasma-ion mobility spectrometry apparatus. The low-temperature plasma ionization source further comprises a preheating device (2) installed on the pipeline of the discharge gas inlet pipe (1).

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