A portable gas chromatograph integrated with freeze enrichment-thermal desorption pretreatment

Abstract

The application discloses a kind of integrated refrigeration enrichment-thermal desorption pretreatment portable gas chromatograph, belong to environmental monitoring analytical instrument technical field.The application is arranged in the instrument shell gas delivery and multi-working condition gas path control unit, refrigeration enrichment and thermal desorption integrated pretreatment unit, chromatographic separation unit and detection unit;Refrigeration enrichment and thermal desorption integrated pretreatment unit includes staged temperature control refrigeration enrichment component and micro-tube thermal desorption component, and staged temperature control refrigeration enrichment component is constituted by inner layer semiconductor active refrigeration subunit and outer layer heat insulation temperature control subunit, and micro-tube thermal desorption component includes micro-adsorption tube, heating unit and double temperature sensor temperature measurement structure;Through multi-working condition gas path switching, enrichment, thermal desorption, sampling, cleaning and non-enrichment sampling mode are realized.The application improves the detection sensitivity and analysis stability of trace volatile organic compounds under the premise of not significantly increasing the volume and power consumption of instrument.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring and analysis instrument technology, and in particular relates to a portable gas chromatograph that integrates cryogenic enrichment-thermal desorption pretreatment. Background Technology

[0002] Portable gas chromatographs are widely used in on-site environmental monitoring, emergency accident assessment, and industrial health and safety applications due to their small size, light weight, and portability, especially for the rapid analysis of volatile organic compounds (VOCs) in the air. Although existing portable gas chromatographs can achieve on-site detection, significant limitations remain when dealing with trace levels of VOCs.

[0003] Existing portable gas chromatographs, when used for on-site volatile organic compound (VOC) analysis, are limited by simple pretreatment methods and limited enrichment efficiency at room temperature, making it difficult to achieve highly sensitive and stable monitoring of trace VOCs. Traditional portable instruments typically only have simple pretreatment methods such as filtration or room-temperature adsorption. At room temperature, the enrichment efficiency of adsorbents for VOCs is limited, resulting in a large number of low-concentration target components not being effectively captured, directly affecting the sensitivity of subsequent detection. Due to the lack of an efficient concentration step, the sample concentration entering the chromatographic column is low, making it difficult to generate a sufficiently strong detection signal for trace VOCs, failing to meet increasingly stringent monitoring standards. Furthermore, the simple enrichment process is susceptible to changes in ambient temperature and humidity, leading to poor repeatability of the enrichment and desorption processes, unstable analytical results, and reduced reliability.

[0004] Furthermore, integrating an efficient and controllable enrichment and desorption system while maintaining portability—namely, small size, low power consumption, and light weight—is a technical challenge. Traditional laboratory-grade sample preparation equipment is bulky and energy-intensive, making it impossible to directly adapt to portable instruments. Therefore, there is an urgent need for a new type of portable gas chromatograph that can significantly improve the sensitivity, stability, and repeatability of trace volatile organic compound detection without sacrificing portability. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a portable gas chromatograph that integrates cryogenic enrichment and thermal desorption pretreatment, thereby resolving the issues present in the prior art.

[0006] To achieve the above objectives, the present invention provides a portable gas chromatograph integrating cryogenic enrichment-thermal desorption pretreatment, comprising an instrument housing and a chromatographic separation unit and a detection unit disposed within the instrument housing, characterized in that it further comprises: The gas delivery and multi-condition gas path control unit is used to introduce ambient gas, carrier gas and cleaning gas and switch the gas path status. The integrated pretreatment unit for cryogenic enrichment and thermal desorption includes a staged temperature-controlled cryogenic enrichment component and a micro-tube thermal desorption component. The graded temperature-controlled cryogenic enrichment component includes an inner active cooling subunit and an outer thermal isolation temperature control subunit. The inner active cooling subunit is used to cool the micro-adsorption tube, and the thermal isolation temperature control subunit is disposed between the micro-adsorption tube and the external environment. The microtubular thermal desorption assembly includes the micro-adsorption tube and a heating unit, wherein the heating unit is fitted to the outer wall of the micro-adsorption tube.

[0007] Optionally, the gas delivery and multi-condition gas path control unit includes a sampling and gas supply control subunit and a multi-condition gas path switching subunit; The sampling and gas supply control subunit includes an ambient gas inlet, a carrier gas inlet, a cleaning gas inlet, multiple solenoid valves, an electric six-way valve, a mass flow meter, and a diaphragm sampling pump. The multi-condition gas path switching subunit is arranged around the integrated pretreatment unit for cryogenic enrichment and thermal desorption. The multi-condition gas path switching subunit includes an enrichment main gas path submodule, an enrichment bypass submodule, and a cleaning gas path submodule. The enrichment bypass submodule is arranged in parallel with the enrichment main gas path submodule.

[0008] Optionally, the inner active cooling subunit includes a semiconductor refrigeration chip, the cold end of which is in contact with the micro-adsorption tube through a high thermal conductivity connector, and the hot end of which is thermally coupled to a heat dissipation system consisting of a heat sink and a fan.

[0009] Optionally, the thermal insulation temperature control subunit is an aerogel insulation layer covering the periphery of the micro-adsorption tube.

[0010] Optionally, the thermal isolation temperature control subunit is a sealed outer shell disposed around the micro adsorption tube, and a closed gas thermal insulation cavity is formed between the outer shell and the micro adsorption tube.

[0011] Optionally, the microtubular thermal desorption assembly further includes a temperature detection unit, which includes a first temperature sensor disposed inside the micro-adsorption tube or in the vicinity of the adsorbent bed, and a second temperature sensor disposed on the outer wall of the micro-adsorption tube.

[0012] Optionally, the enrichment bypass submodule includes a micro quartz tube, which has the same specifications as the micro adsorption tube and is not filled with adsorbent. In non-enrichment conditions or standby mode, the solenoid valve corresponding to the enrichment bypass submodule is opened and the solenoid valve corresponding to the enrichment main gas path is closed, so that the gas flow passes through the micro quartz tube without entering the micro adsorption tube.

[0013] Optionally, the cleaning gas circuit submodule is connected to the micro-adsorption tube via an independently configured cleaning solenoid valve; in the cleaning and regeneration operation, the cleaning solenoid valve is opened, and the cleaning gas enters the adsorbent bed from the outlet end of the micro-adsorption tube in the reverse direction.

[0014] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides a portable gas chromatograph integrating cryogenic enrichment and thermal desorption pretreatment. The portable gas chromatograph integrates a single pretreatment unit for cryogenic enrichment and thermal desorption, and features a holistic and coordinated design for sampling, gas path switching, chromatographic separation, and detection processes. This allows for the enrichment of trace volatile organic compounds in ambient gases before analysis, followed by controlled release and injection during the analysis phase. This improves effective injection concentration and detection sensitivity without increasing sampling volume. Simultaneously, this integrated design maintains analytical performance without significantly increasing instrument size, weight, or energy consumption, enhancing the instrument's applicability in on-site monitoring, emergency monitoring, and mobile monitoring. This invention utilizes dual temperature sensors to simultaneously monitor the temperature of the adsorbent bed and the wall of the micro-adsorption tube, enabling the identification and early correction of temperature deviations caused by heat transfer hysteresis. This improves the temperature control accuracy and repeatability of the cryogenic enrichment and thermal desorption processes. The staged temperature-controlled cryogenic enrichment structure effectively reduces environmental thermal disturbance and cooling energy consumption, enhancing the instrument's operational stability and endurance under portable application conditions. This invention, by setting up a multi-condition gas path switching structure including an enrichment main gas path submodule, an enrichment bypass submodule, and a cleaning gas path submodule, enables the micro-adsorption tube to selectively connect and isolate at different working stages, avoiding interference from ambient air, water vapor, and residual volatile organic compounds on the adsorbent bed. It also allows for effective purging of the adsorption tube and related pipelines during cleaning and regeneration, thereby reducing baseline drift and improving stability and reliability during multiple cycle detection processes. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a portable gas chromatograph integrating cryogenic enrichment-thermal desorption pretreatment according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the instrument's gas path structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the instrument gas path enrichment stage according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the thermal desorption stage of the instrument gas path in an embodiment of the present invention; Figure 5This is a schematic diagram of the gas path injection stage of the instrument according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the non-enrichment sample introduction stage of the instrument gas path in an embodiment of the present invention; Figure 7 This is a schematic diagram of the instrument gas path cleaning stage in an embodiment of the present invention; Figure 8 This is a schematic diagram of the active cooling subunit in the integrated pretreatment unit for cryogenic enrichment and thermal desorption according to an embodiment of the present invention. Figure 9 This is a schematic diagram of the structure of two thermally isolated temperature control subunits in the integrated pretreatment unit for cryogenic enrichment and thermal desorption according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the microtubular thermal desorption component in the integrated pretreatment unit for cryogenic enrichment and thermal desorption according to an embodiment of the present invention. Figure 11 The standard gas test results diagram of this invention is shown in the figure (benzene, toluene, ethylbenzene, m-xylene and o-xylene are labeled as 1, 2, 3, 4 and 5 respectively). Figure 12 This is a schematic diagram of the thermal desorption temperature change curves under different temperature control methods in an embodiment of the present invention; Figure 13 This is a schematic diagram illustrating the baseline stability changes before and after the cleaning process in an embodiment of the present invention. Among them, 1-instrument housing, 2-LCD display screen, 3-ambient gas inlet, 4-carrier gas inlet, 5-cleaning gas inlet, 6-triangle socket, 7-two-pin aviation plug, 8-fan cover, 9-integrated pretreatment unit for cryogenic enrichment and thermal desorption, 10-No. 1 three-way solenoid valve, 11-No. 2 three-way solenoid valve, 12-No. 1 two-way solenoid valve, 13-No. 2 two-way solenoid valve, 14-No. 3 two-way solenoid valve, 15-No. 1 mass flow meter, 16-No. 2 mass flow meter, 17-No. 3 mass flow meter, 18-electric 19-Six-way valve, 20-Chromatographic separation unit, 21-Detection unit, 22-Diameter sampling pump, 23-Control circuit board, 24-Power supply module, 25-Micro adsorption tube, 26-Micro quartz tube, 27-Quantitative ring, 28-Adsorbent bed, 29-Semiconductor cooling chip, 30-High thermal conductivity connector, 31-DC micro fan, 32-Thermal conductive silicone grease, 33-Aerogel insulation sleeve, 34-Gas insulation cavity, 35-Heating unit, 36-First temperature sensor, 37-Second temperature sensor. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0017] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0018] This embodiment provides a portable gas chromatograph integrating cryogenic enrichment-thermal desorption pretreatment, including an instrument housing and a chromatographic separation unit and a detection unit disposed within the instrument housing, characterized in that it further includes: The gas delivery and multi-condition gas path control unit is used to introduce ambient gas, carrier gas and cleaning gas and switch the gas path status. The integrated pretreatment unit for cryogenic enrichment and thermal desorption includes a staged temperature-controlled cryogenic enrichment component and a micro-tube thermal desorption component. The graded temperature-controlled cryogenic enrichment component includes an inner active cooling subunit and an outer thermal isolation temperature control subunit. The inner active cooling subunit is used to cool the micro-adsorption tube, and the thermal isolation temperature control subunit is disposed between the micro-adsorption tube and the external environment. The microtubular thermal desorption assembly includes the micro-adsorption tube and a heating unit, wherein the heating unit is fitted to the outer wall of the micro-adsorption tube.

[0019] Furthermore, the gas delivery and multi-condition gas path control unit includes a sampling and gas supply control subunit and a multi-condition gas path switching subunit. The sampling and gas supply control subunit includes an ambient gas inlet, a carrier gas inlet, a cleaning gas inlet, multiple solenoid valves, an electric six-way valve, a mass flow meter, and a diaphragm sampling pump. The multi-condition gas path switching subunit is arranged around the integrated pretreatment unit for cryogenic enrichment and thermal desorption. The multi-condition gas path switching subunit includes an enrichment main gas path submodule, an enrichment bypass submodule, and a cleaning gas path submodule. The enrichment bypass submodule is arranged in parallel with the enrichment main gas path submodule.

[0020] Furthermore, the inner active cooling subunit includes a semiconductor cooling chip, the cold end of which is in contact with the micro-adsorption tube through a high thermal conductivity connector, and the hot end of which is thermally coupled to a heat dissipation system consisting of a heat sink and a fan.

[0021] Furthermore, the thermal insulation temperature control subunit is an aerogel insulation layer covering the periphery of the micro-adsorption tube.

[0022] Furthermore, the thermal isolation temperature control subunit is a sealed outer shell disposed around the micro adsorption tube, and a closed gas thermal insulation cavity is formed between the outer shell and the micro adsorption tube.

[0023] Furthermore, the microtubular thermal desorption assembly also includes a temperature detection unit, which includes a first temperature sensor disposed inside the micro-adsorption tube or in the vicinity of the adsorbent bed, and a second temperature sensor disposed on the outer wall of the micro-adsorption tube.

[0024] Furthermore, the enrichment bypass submodule includes a micro quartz tube, which has the same specifications as the micro adsorption tube and is not filled with adsorbent. In non-enrichment operation or standby mode, the solenoid valve corresponding to the enrichment bypass submodule is opened and the solenoid valve corresponding to the enrichment main gas path is closed, so that the gas flow passes through the micro quartz tube without entering the micro adsorption tube.

[0025] Furthermore, the cleaning gas circuit module is connected to the micro-adsorption tube via an independently configured cleaning solenoid valve; during the cleaning and regeneration process, the cleaning solenoid valve is opened, and the cleaning gas enters the adsorbent bed from the outlet end of the micro-adsorption tube in the reverse direction.

[0026] Specifically, the implementation process of this embodiment includes: like Figure 1 As shown, this application provides a portable gas chromatograph with integrated cryogenic enrichment-thermal desorption pretreatment. The specific structure includes: a small-sized instrument housing 1; an LCD screen 2 embedded in the housing; an ambient gas inlet 3; a carrier gas inlet 4; a cleaning gas inlet 5; a T-shaped socket 6; a two-pin aviation plug 7; a fan cover 8; and installed within the housing are a No. 1 three-way solenoid valve 10, a No. 2 three-way solenoid valve 11, a No. 1 two-way solenoid valve 12, a cryogenic enrichment and thermal desorption integrated pretreatment unit 9, a No. 2 two-way solenoid valve 13, a No. 3 two-way solenoid valve 14, a No. 1 mass flow meter 15, a No. 2 mass flow meter 16, a No. 3 mass flow meter 17, an electric six-way valve 18, a chromatographic separation unit 19, a detection unit 20, a diaphragm sampling pump 21, a control circuit board 22, and a power supply module 23.

[0027] The LCD screen 2, along with the ambient gas inlet 3, carrier gas inlet 4, and cleaning gas inlet 5, are mounted on the front of the instrument housing 1. Real-time monitoring results and instrument operating parameters can be obtained from the LCD screen 2. A three-prong socket 6 and a two-pin aviation connector 7 are mounted on the side of the instrument, their height depending on the location of the power supply module 23. Both must be flush with the power input terminal of the power supply module 23. The power supply module 23 can accept a maximum input of 220V AC or 24V DC. AC power is input through the three-prong socket 6, and DC power through the two-pin aviation connector 7. The power supply module 23 outputs DC power. For field experiments, a portable AC power supply or a lithium battery can be used. A fan shroud 8 is mounted on the back of the instrument, its height depending on the location of the integrated cryogenic enrichment and thermal desorption pretreatment unit 9. The fan shroud 8 is flush with the heat dissipation end of the integrated cryogenic enrichment and thermal desorption pretreatment unit 9.

[0028] The following components are connected to the main control circuit board 22 via signal circuits: No. 1 three-way solenoid valve 10, No. 2 three-way solenoid valve 11, No. 1 two-way solenoid valve 12, integrated pretreatment unit for cryogenic enrichment and thermal desorption 9, No. 2 two-way solenoid valve 13, No. 3 two-way solenoid valve 14, No. 1 mass flow meter 15, No. 2 mass flow meter 16, No. 3 mass flow meter 17, electric six-way valve 18, chromatographic separation unit 19, detection unit 20, diaphragm sampling pump 21, and solenoid valve 22.

[0029] The portable gas chromatograph with integrated cryogenic enrichment-thermal desorption pretreatment module includes a gas delivery and multi-condition gas path control unit. This unit is used to uniformly regulate the ambient gas and carrier gas, and to achieve orderly organization and reliable switching of the gas path under different working conditions such as cryogenic enrichment, thermal desorption injection, bypass isolation and online cleaning.

[0030] The gas delivery and multi-condition gas path control unit includes a sampling and gas supply control subunit and a multi-condition gas path switching subunit. The sampling and gas supply control subunit includes a sampling pump, a mass flow controller, a solenoid valve, a pipeline temperature control assembly, and pipeline connection assemblies. The sampling pump is preferably a miniature diaphragm pump or a brushless DC gas pump, with a rated flow rate of 50–300 mL / min. -1 The operating voltage is 5–12 V to meet the requirements of stable pumping capacity and low power consumption for portable applications; the mass flow controller is preferably a thermal mass flow controller with a range of 0–200 mL·min. -1 The flow control accuracy is better than ±2%, which is used to precisely adjust the flow rate of ambient gas or carrier gas entering the pretreatment unit.

[0031] The pipeline connection components preferably use inert polymer pipelines or PEEK pipelines with an inner diameter of 1.0–2.0 mm, and modular connections are achieved through quick-connect fittings; the pipeline temperature control components are set in key gas passage sections to provide appropriate insulation or anti-condensation control for the gas passage during low-temperature enrichment or high-temperature desorption processes, and their temperature control range is preferably 40–60 ℃.

[0032] The multi-condition gas path switching subunit consists of the internal piping of the integrated pretreatment unit 9 for cryogenic enrichment and thermal desorption, and solenoid valves arranged around the inlet and outlet ends of the internal piping. The solenoid valves are preferably low dead volume straight-through and three-way miniature solenoid valves, and their internal cavity volume is preferably less than 50 μL to reduce the gas path stagnation volume.

[0033] The solenoid valves are arranged in a multi-way valve array and are uniformly driven and controlled by the main control unit. By programmatically combining and controlling the on and off states of each solenoid valve, the inlet and outlet ends of the micro-adsorption tube 24 can be quickly and repeatedly switched between different gas channels, thus reconstructing the gas transmission path.

[0034] The multi-condition gas path switching subunit includes a main gas path enrichment submodule, a bypass enrichment submodule, and a cleaning gas path submodule.

[0035] The enrichment main gas path submodule consists of at least one set of micro-adsorption tubes 24, an injection solenoid valve, and an outlet solenoid valve connected in series. Under cryogenic enrichment conditions, the injection solenoid valve switches to the ambient gas path. The ambient gas enters through the inlet end of the adsorption tube under the drive of the sampling pump and flows along the adsorbent bed 27, so that the target component is adsorbed and enriched under low temperature conditions. Under thermal desorption injection conditions, the injection solenoid valve switches to the carrier gas path. The carrier gas flows through the adsorption tube under controlled flow conditions and carries the target component to the chromatographic separation unit 19 during the heating of the adsorbent bed 27.

[0036] The enrichment bypass submodule is connected in parallel with the enrichment main gas path submodule, and it consists of at least one set of miniature quartz tubes 25 and bypass solenoid valves connected in series. The miniature quartz tubes 25 and miniature adsorption tubes 24 have the same specifications and are not filled with adsorbent. When the instrument is in non-enrichment mode, standby mode, or transport mode, the bypass solenoid valve is open, while the corresponding solenoid valve of the enrichment main gas path is closed, allowing ambient gas or carrier gas to pass directly through the miniature quartz tubes 25 via the bypass without entering the miniature adsorption tubes 24. This isolates the adsorbent bed 27 from the instrument's main gas path and the external environment, reducing the impact of ambient moisture and background VOCs on the adsorbent performance.

[0037] The cleaning gas path submodule is connected to the micro-adsorption tube 24 via an independently configured cleaning solenoid valve and cleaning gas interface. During cleaning and regeneration, the cleaning solenoid valve is opened, allowing cleaning gas or reverse carrier gas to enter the adsorbent bed 27 from the outlet of the adsorption tube, purging the adsorbent and its upstream and downstream gas paths. The cleaning gas flow rate is preferably controlled between 50 and 150 mL / min. -1 This is to ensure the cleaning effect while avoiding disturbance to the structure of the adsorbent.

[0038] Through the above structural design, the gas delivery and multi-condition gas path control unit can achieve stable switching of multiple working gas paths in a compact space, providing reliable gas conditions for the pretreatment process of cryogenic enrichment and thermal desorption, which is suitable for the application needs of portable gas chromatographs in field and mobile monitoring environments.

[0039] like Figure 2 As shown, this invention also provides a gas path design scheme for a portable gas chromatograph integrating a cryogenic enrichment-thermal desorption pretreatment module. The electric six-way valve 18 has six ports (1, 2, 3, 4, 5, and 6), and the first three-way solenoid valve 10 and the second three-way solenoid valve 11 have three ports (A, P, and E). Port A of the first three-way solenoid valve 10 is connected to the ambient gas inlet 3, port E is connected to the carrier gas inlet 4, and port P is connected to port P of the second three-way solenoid valve 11. Port A of the second three-way solenoid valve 11 is connected to the inlet of the micro-quartz tube 25 in the integrated cryogenic enrichment and thermal desorption pretreatment unit 9, port E is connected to the inlet of the first two-way solenoid valve 12, and the outlet of the first two-way solenoid valve 12 is connected to the inlet of the micro-adsorption tube 24 in the integrated cryogenic enrichment and thermal desorption pretreatment unit 9. The outlet of the miniature quartz tube 25 is connected to the inlet of the first mass flow meter 15. The outlet of the miniature adsorption tube 24 is connected to the inlet of the second two-way solenoid valve 13. The outlet of the second two-way solenoid valve 13 is connected to the inlet of the second mass flow meter 16. The outlets of the first and second mass flow meters 15 and 16 are simultaneously connected to the outlet of the third two-way solenoid valve 14 and the first air port of the electric six-way valve 18 via a three-way connector. The second and fifth air ports of the electric six-way valve 18 are connected to the metering ring 26, and the sixth air port is connected to the inlet of the diaphragm sampling pump 21. The inlet of the third mass flow meter 17 is connected to the carrier gas inlet 4, and its outlet is connected to the fourth air port of the electric six-way valve 18. The third air port of the electric six-way valve 18 is connected to the inlet of the chromatographic separation unit 19, and the outlet of the chromatographic separation unit 19 is connected to the detection unit 20.

[0040] The three-way solenoid valve has two states: energized and de-energized. When energized, air port A is connected to air port P, and when de-energized, air port P is connected to air port E.

[0041] The electric six-way valve 18 has two states: open and closed. When open, air holes 1 and 2, 3 and 4, and 5 and 6 are connected; when closed, air holes 1 and 6, 2 and 3, and 4 and 5 are connected.

[0042] like Figures 3-7 As shown, based on the above gas path structure, the portable gas chromatograph of this embodiment achieves five working modes—enrichment, thermal desorption, injection, non-enrichment injection, and cleaning—by controlling the on / off states of the three-way solenoid valve, the two-way solenoid valve, and the electric six-way valve 18. The details are as follows: During the enrichment stage, the first three-way solenoid valve 10 is energized, the second three-way solenoid valve 11 is de-energized, the first two-way solenoid valve 12 and the second two-way solenoid valve 13 are open, the third two-way solenoid valve 14 is closed, and the electric six-way valve 18 is open. The ambient gas to be tested enters through the ambient gas inlet 3, then sequentially passes through the first three-way solenoid valve 10 and the second three-way solenoid valve 11 into the micro-adsorption tube 24. The micro-adsorption tube 24 is in a cooled state, achieving low-temperature capture of the target component. Subsequently, the gas flows through the second two-way solenoid valve 13 and the second mass flow meter 16 into the three-way connector, enters the electric six-way valve 18, and is finally extracted and discharged by the diaphragm sampling pump 21. This gas path achieves effective enrichment of the sample gas on the adsorbent bed 27.

[0043] After enrichment is complete, the thermal desorption stage begins. The first three-way solenoid valve 10 is de-energized, allowing the carrier gas to enter the system through the carrier gas inlet 4 and then through the first three-way solenoid valve 10 into the subsequent gas path. The second three-way solenoid valve 11 remains de-energized, allowing the carrier gas to enter the micro-adsorption tube 24. At this time, the micro-adsorption tube 24 switches from a cooling state to a heating state, rapidly desorbing the target component adsorbed in the bed and flowing out with the carrier gas. It then enters the three-way connector via the second mass flow meter 16 and is introduced into the electric six-way valve 18. With the electric six-way valve 18 open, the metering loop 26 is filled, achieving quantitative loading of the sample gas.

[0044] Once the quantitative loop 26 is filled with desorbed gas, the control unit drives the electric six-way valve 18 to switch from the open state to the closed state. The carrier gas enters the No. 4 port of the electric six-way valve 18 through the No. 3 mass flow meter 17, and then enters the chromatographic separation unit 19 through the No. 3 port. At the same time, the desorbed gas in the quantitative loop 26 is carried into the chromatographic separation unit 19 by the carrier gas for separation and analysis. The separated components enter the detection unit 20 for detection, thereby realizing the quantitative injection analysis of thermally desorbed samples.

[0045] After analysis, the system enters the cleaning phase. The first three-way solenoid valve 10 is energized, all two-way solenoid valves remain open, and the electric six-way valve 18 is open. Cleaning gas flows in through the third two-way solenoid valve 14, passing through the miniature quartz tube 25, the miniature adsorption tube 24, and the metering ring 26, continuously purging residual gas inside the system. The gas is then discharged from the ambient gas inlet 3 and the diaphragm sampling pump 21, thereby eliminating the influence of residual components on the next detection and improving the stability of repeated measurements.

[0046] When the concentration of the target substance in the environment is high (ppm level), the ambient gas does not need to be enriched by the micro-adsorption tube 24 and can be directly input into the chromatographic separation unit 19. During non-enrichment injection, the first three-way solenoid valve 10 and the second three-way solenoid valve 11 are energized, the first two-way solenoid valve 12, the second two-way solenoid valve 13, and the third two-way solenoid valve 14 are closed, and the electric six-way valve 18 is open. The ambient gas to be tested enters through the ambient gas inlet 3, then sequentially passes through the first three-way solenoid valve 10 and the second three-way solenoid valve 11 into the micro-quartz tube 25. Subsequently, the gas flows through the first mass flow meter 15 into the three-way connector and into the electric six-way valve 18, filling the quantitative loop 26. Then, the electric six-way valve 18 switches from open to closed, and the ambient gas in the quantitative loop 26 is carried by the carrier gas into the chromatographic separation unit 19 for separation and analysis. The separated components then enter the detection unit 20 for detection.

[0047] Through the above continuous control process, this embodiment achieves integrated operation of enrichment, desorption, injection, quantification and analysis under the same gas path structure, and can complete multi-mode conversion without adding additional switching pipelines or complex mechanical structures.

[0048] The integrated pretreatment unit 9 for cryogenic enrichment and thermal desorption is used for low-temperature enrichment and controlled thermal desorption release of VOCs in ambient gases with volume fractions of ppb or even ppt. Its overall structural dimensions are preferably controlled within the range of 80–150 mm (axial length) and 60–90 mm (radial diameter), and the continuous operation power consumption is preferably no more than 100 W to meet the long-term stable operation requirements of portable gas chromatographs in the field and on mobile platforms.

[0049] The integrated pretreatment unit 9 for cryogenic enrichment and thermal desorption includes a staged temperature-controlled cryogenic enrichment component and a micro-tube thermal desorption component. The staged temperature-controlled cryogenic enrichment component is used to stably control the temperature of the micro-adsorption tube 24 within the range of -20 to 10 ℃ during the enrichment stage, and the micro-tube thermal desorption component is used to rapidly raise the temperature of the adsorbent bed 27 to 150 to 300 ℃ during the desorption stage.

[0050] The graded temperature-controlled cryogenic enrichment component consists of an inner active cooling subunit and an outer thermally isolated temperature-controlled subunit.

[0051] like Figure 8 As shown, the active cooling subunit adopts an attached thermal coupling structure. A semiconductor cooling chip 28 is disposed on the outside of the micro-adsorption tube 24. Its cold end forms a low thermal resistance heat transfer interface with the outer wall of the adsorption tube via a high thermal conductivity connector 29. The hot end is connected to a heat dissipation system consisting of a heat sink 30 and a DC micro fan 31, thereby establishing an active heat transfer channel for directional transfer from the adsorption tube to the environment. The inner active cooling subunit includes a single-stage or multi-stage semiconductor cooling chip 28. The cooling power of a single stage is preferably 15–40 W, and the size is preferably 20×20 mm or 30×30 mm. The thickness of the high thermal conductivity connector 29 is preferably 1–3 mm, and it can be made of copper or aluminum alloy, with a thermal conductivity preferably not less than 260 W·m. -1 ·K -1 Thermal grease 32 is applied at the interface to control the contact thermal resistance to 0.1 K·W. -1 The following describes the heat dissipation system, which includes a heat sink 30 and a DC micro fan 31. The fin spacing of the heat sink 30 is preferably 5–7 mm, and the rated airflow of the fan is preferably 3–8 CFM, to ensure that the temperature rise of the hot end does not exceed 15 ℃ of the ambient temperature under continuous cooling conditions.

[0052] like Figure 9 As shown, the thermal isolation temperature control subunit is arranged around the micro-adsorption tube 24 and the active cooling component, forming a stable thermal insulation state after assembly, eliminating the need for continuous energy consumption during instrument operation. Depending on the insulation mechanism, the thermal isolation temperature control subunit can employ either an aerogel insulation structure or a closed gas insulation structure.

[0053] In a preferred embodiment, the thermal isolation and temperature control subunit is implemented using an aerogel insulation structure. Specifically, an integrally formed or separately assembled aerogel insulation sleeve 33 is provided around the micro-adsorption tube 24 and its active cooling component. The axial length of the insulation sleeve preferably covers the entire length of the adsorbent bed 27 and extends 5–10 mm to both ends to reduce heat conduction at the ends. The aerogel material is preferably a silica-based flexible aerogel felt or block aerogel with an apparent density of 120–200 kg·m³. -3 The thermal conductivity at room temperature is 0.005–0.015 W·m. -1 ·K -1 The radial thickness of the insulation layer is preferably 5–15 mm. To improve mechanical strength and suppress aerogel powdering or debris shedding, the outer side of the aerogel insulation sleeve 33 may be covered with a thin-walled metal shell or heat-resistant engineering plastic shell with a thickness not exceeding 0.5 mm. This shell only serves as structural support and sealing and does not participate in heat conduction as a main insulation layer.

[0054] In another preferred embodiment, the thermal isolation temperature control subunit is implemented using a closed gas insulation structure. Specifically, a sealed outer shell is provided around the micro-adsorption tube 24 and the active cooling subunit, forming a closed low thermal conductivity gas insulation cavity 34 between the outer shell and the adsorption tube, with a radial thickness preferably of 20–50 mm. The gas filled in the insulation cavity is preferably an inert gas or a low thermal conductivity gas with a thermal conductivity lower than that of air, and / or air, nitrogen, argon, or a combination thereof under normal or near-normal pressure conditions, to effectively reduce radial heat transfer flux without introducing additional energy consumption. The outer shell is preferably made of heat-resistant engineering plastic or composite material, with a wall thickness controlled within the range of 5–10 mm, to minimize the impact of solid thermal conductivity on the overall insulation performance while ensuring structural strength and airtightness. After assembly, the closed gas insulation cavity 34 is isolated from the external environment through a sealed structure, keeping the gas inside the cavity in a static or quasi-static state, thereby effectively suppressing natural convection heat transfer. The axial length of the insulation cavity is preferably matched with the length of the adsorbent bed 27, and its inner wall surface can be coated with a low emissivity coating, a metallized reflective layer or polished to further reduce the contribution of radiative heat transfer.

[0055] Under steady-state conditions, the heat transfer process between the working area of ​​the adsorption tube and the external environment can be approximated as one-dimensional radial heat transfer, which is the steady-state heat flow from the environment to the adsorbent bed 27. Q Represented as: ; in, Q The steady-state thermal power (W) transferred to the adsorbent bed 27; T ads The steady-state operating temperature (K) of adsorbent bed 27; T amb The external ambient temperature of the device (K); R th The equivalent total thermal resistance between the adsorption tube and the environment (K·W) -1 ).

[0056] Equivalent total thermal resistance R th It is composed of the thermal resistance of each layer of the insulation structure in series with the convective heat transfer resistance of the outer surface, and is expressed as: ; in, δ i The effective radial thickness (m) of the i-th layer of thermal insulation structure; λ i The equivalent thermal conductivity (W·m) of the corresponding i-th layer of material or medium -1 ·K -1 ); A The equivalent heat transfer area (m²) of the adsorption tube working zone 2), which can be approximated as the cylindrical side surface area corresponding to the adsorbent bed 27; h The combined convective heat transfer coefficient (W·m) between the outermost surface of the insulation structure and the ambient air. -2 ·K -1 ).

[0057] In aerogel insulation structures, λ i The thermal conductivity of aerogel materials is mainly determined by their low solid-state thermal conductivity and the inhibition of gas heat transfer by their nanopores; in closed gas insulation structures, λ i It corresponds to the equivalent thermal conductivity of a stationary or quasi-stationary gas within a closed cavity, and includes the equivalent contribution of radiative heat transfer.

[0058] Within a typical structural parameter range of the present invention, the length of the adsorbent bed 27 of the micro-adsorption tube 24 is preferably 30–60 mm, and the outer diameter is 4–6 mm, corresponding to an equivalent heat transfer area. A Approximately 4×10 -4 –1×10 -3 m 2 Radial thickness of aerogel insulation layer or enclosed gas insulation cavity δ i Preferably 5–15 mm; outer surface convective heat transfer coefficient h Under natural convection conditions, it is typically 5–15 W·m⁻¹ -2 ·K -1 Within the specified range, substituting the above structural parameters and material thermal conductivity into the equivalent thermal resistance model allows for the calculation of the equivalent thermal resistance between the adsorption tube and the environment. R th Increase to approximately 10–40 K·W -1 The scope of the project.

[0059] Therefore, under cryogenic enrichment conditions, when the temperature difference between the adsorbent bed 27 and the environment... ΔT=T ads -T amb When the steady-state heat load is constant, the heat load transferred to the cooling end is... Q The effective thermal resistance decreases significantly with the increase of the equivalent thermal resistance, thereby reducing the steady-state input power required by the semiconductor cooler 28 to maintain the low-temperature enrichment state by more than 30%, thus effectively improving the overall energy efficiency of the system and extending the battery life of portable devices.

[0060] like Figure 10As shown, the microtubular thermal desorption assembly includes a micro-adsorption tube 24, a heating unit 35, a first temperature sensor 36, and a second temperature sensor 37. The micro-adsorption tube 24 is preferably made of stainless steel or quartz, with an inner diameter of 3–5 mm. It is filled with an adsorbent for adsorbing target VOCs, and the specific parameters are matched and optimized according to the boiling point, polarity, and sampling volume of the target component.

[0061] The heating unit 35 is preferably disposed on the outside of the micro-adsorption tube 24, and is preferably in the form of a thin-film resistance heating structure, a flexible polyimide heating film, or a wire-wound resistance heating element, and is arranged continuously or in sections along the axial direction of the micro-adsorption tube 24. The heating unit 35 is preferably tightly bonded to the outer wall of the micro-adsorption tube 24 by a highly thermally conductive insulating adhesive layer, the thickness of which is preferably 50–200 μm, and the thermal conductivity is preferably not less than 1.0 W·m. -1 ·K -1 This is to reduce interfacial thermal resistance and ensure uniform heat transfer in the axial and radial directions.

[0062] In a preferred embodiment, the rated heating power of the heating unit 35 is preferably 15–30 W, and the heating power per unit length is preferably 0.5–3 W·cm. -1 The temperature can be continuously adjusted within the range of 0–100%. The heating unit 35 is used during the thermal desorption stage to maintain the temperature of the adsorbent bed 27 at 5–50 °C·s. -1 The heating rate increases rapidly and maintains a preset desorption temperature plateau within the range of 150–300 °C. The plateau holding time is preferably 10–120 s to ensure sufficient desorption of the target component without causing excessive broadening of the chromatographic peak.

[0063] Furthermore, the heating unit 35 and the aforementioned active cooling subunit are structurally integrated, and the two are arranged outward in sequence with the micro adsorption tube 24 as the axis, so that the same micro adsorption tube 24 can quickly switch between low temperature enrichment state and high temperature desorption state in different working stages.

[0064] The temperature detection unit 20 includes a first temperature sensor 36 and a second temperature sensor 37. The first temperature sensor 36 is disposed inside the micro-adsorption tube 24 or in the vicinity of the adsorbent bed 27, preferably a micro thermocouple, and is used to obtain local temperature information of the adsorbent bed 27. The second temperature sensor 37 is disposed on the outer wall of the micro-adsorption tube 24 or in the vicinity of it, and is used to obtain tube wall temperature information.

[0065] Because a radial temperature gradient exists within the adsorbent bed 27, a transient difference exists between the internal temperature of the bed and the tube wall temperature due to thermal resistance during rapid cooling or heating. A single measuring point temperature is insufficient to accurately characterize the overall equivalent operating temperature state of the bed. Therefore, this system constructs an equivalent temperature estimation model based on dual measuring point temperature information to improve the accuracy of temperature control.

[0066] Specifically, the actual temperature of the adsorbent bed 27 T real Represented as, ; in, T 1 The local temperature of the adsorbent bed 27 is measured by the first temperature sensor 36. T 2 The pipe wall temperature is measured by the second temperature sensor 37. k The correction factor is related to the heat capacity of the adsorbent, the wall thickness of the tube, and the interfacial thermal resistance. Its value is preferably determined by calibration and is usually in the range of 0.1–0.5.

[0067] During the rapid temperature change phase, the system further introduces a temperature change rate compensation term to correct the dynamic deviation caused by heat transfer hysteresis. Its expression is: ; in, τ The equivalent thermal time constant is preferably 1–5 s. This compensation term is used to characterize the effect of internal thermal inertia on temperature measurement, thereby improving the accuracy of temperature estimation during rapid enrichment or desorption phases.

[0068] In a further embodiment, the heating unit 35 is electrically connected to the temperature detection unit 20, and its output power and heating rate are adjusted in real time by the main control unit based on the temperature information obtained by the first temperature sensor 36 and the second temperature sensor 37. The main control unit preferably uses an equivalent actual operating temperature. T real As the control target quantity, and combined with the temperature change rate, the heating power is adjusted by feedforward and feedback to keep the temperature overshoot in the desorption stage within ±2℃, thereby improving the repeatability and reliability of the desorption process.

[0069] The present invention also includes a chromatographic separation unit 19, which is used for the sequential separation of target gas components released by the integrated pretreatment unit 9 for cryogenic enrichment and thermal desorption and transported with a carrier gas. The chromatographic separation unit 19 includes one or more chromatographic columns, preferably with a column length of 1–10 m, an inner diameter of 0.1–0.53 mm, a stationary phase film thickness of 0.1–5 μm, and a carrier gas preferably helium or nitrogen, with a flow rate preferably controlled at 0.5–5 mL·min. -1 Within the range.

[0070] The chromatographic separation unit 19 further includes a column temperature control component, which is used for isothermal control or programmed temperature control of the operating temperature of the chromatographic column. The temperature control range is preferably 30–250 °C, and the temperature control accuracy is preferably better than ±0.5 °C. In programmed temperature mode, the column temperature ramp rate is preferably 5–30 °C / min. -1 This is to shorten the analysis cycle while ensuring the separation of substances.

[0071] The present invention also includes a detection unit 20, which is disposed at the outlet end of the chromatographic column and is used to detect the gas components after chromatographic separation. The detection unit 20 includes a gas detector and a signal acquisition component, wherein the gas detector is preferably a photoionization detector (PID) or a flame ionization detector (FID), and the detection limit is preferably below 1 ppb. The sampling frequency of the signal acquisition component is preferably 10–100 Hz, and the acquired detection signal is output to a data processing unit to achieve qualitative identification and quantitative analysis of the target components.

[0072] In this embodiment, a portable gas chromatograph integrating a cryogenic enrichment-thermal desorption pretreatment module is constructed, and its structure is consistent with the aforementioned implementation method.

[0073] The micro-adsorption tube 24 is 45 mm long and 5 mm in outer diameter, filled with 200 mg of Tenax TA adsorbent. The active cooling subunit uses a single-stage 30 W semiconductor cooler 28, with the cold end attached to the adsorption tube via a 2 mm thick copper heat-conducting block. The hot end is equipped with an aluminum heat sink and a 5 CFM DC fan. The thermal isolation temperature control subunit uses a 10 mm thick silica-based flexible aerogel insulation sleeve.

[0074] Under enrichment conditions, the temperature of the adsorbent bed 27 was stably controlled at -10 ℃, the ambient temperature was 27 ℃, and the enrichment flow rate was 100 mL·min. -1 The enrichment time is 120 s.

[0075] During the thermal desorption stage, the heating power was set to 25 W, and the heating rate was approximately 30 °C·s. -1The adsorbent bed 27 was heated to 150 °C within 5 seconds and maintained for 30 seconds.

[0076] The test gas was a standard mixture containing benzene, toluene, ethylbenzene, m-xylene, and o-xylene, with a volume fraction of 50 ppb. The test results are as follows: Figure 11 As shown.

[0077] During the thermal desorption heating process, the internal temperature and the external wall temperature of the adsorption tube were recorded respectively. When the temperature was raised to 150 ℃ during the thermal desorption stage, the bed temperature reached the set value within 5 s, the maximum temperature overshoot was 1.9 ℃, and the steady-state fluctuation range was controlled within ±1 ℃.

[0078] Under the same structural conditions, using a single-point temperature feedback control method, the maximum temperature overshoot during the thermal desorption stage was 7.3 ℃, and the steady-state fluctuation range was ±3 ℃. The results are as follows: Figure 12 As shown.

[0079] The above operational results show that by setting up dual temperature sensors inside and outside the adsorption tube and constructing a dynamic compensation control model, the temperature lag and overshoot during the heating process can be effectively reduced, and the temperature stability and analytical repeatability of the thermal desorption process can be improved.

[0080] After 10 consecutive enrichment-desorption cycles, the blank gas was analyzed. The results showed a slight rise and slow drift in the baseline.

[0081] The cleaning process was then initiated, with the temperature of adsorbent bed 27 raised to 240 °C and maintained for 60 s. After cleaning, a blank test was performed again. The baseline stabilized, no significant drift was observed, the background signal fluctuation amplitude decreased to below 0.5%, and the baseline noise was significantly reduced. Results are as follows: Figure 13 As shown.

[0082] The above results show that by setting a high-temperature cleaning condition, the background accumulation effect generated during the enrichment cycle can be effectively eliminated, thereby improving the stability of continuous system operation and detection accuracy.

[0083] This invention provides a portable gas chromatograph integrating cryogenic enrichment and thermal desorption pretreatment. The portable gas chromatograph integrates a single pretreatment unit for cryogenic enrichment and thermal desorption, and features a holistic and coordinated design for sampling, gas path switching, chromatographic separation, and detection processes. This allows for the enrichment of trace volatile organic compounds in ambient gases before analysis, followed by controlled release and injection during the analysis phase. This improves effective injection concentration and detection sensitivity without increasing sampling volume. Simultaneously, this integrated design maintains analytical performance without significantly increasing instrument size, weight, or energy consumption, enhancing the instrument's applicability in on-site monitoring, emergency monitoring, and mobile monitoring. This invention utilizes dual temperature sensors to simultaneously monitor the temperature of the adsorbent bed and the wall of the micro-adsorption tube, enabling the identification and early correction of temperature deviations caused by heat transfer hysteresis. This improves the temperature control accuracy and repeatability of the cryogenic enrichment and thermal desorption processes. The staged temperature-controlled cryogenic enrichment structure effectively reduces environmental thermal disturbance and cooling energy consumption, enhancing the instrument's operational stability and endurance under portable application conditions. This invention, by setting up a multi-condition gas path switching structure including an enrichment main gas path submodule, an enrichment bypass submodule, and a cleaning gas path submodule, enables the micro-adsorption tube to selectively connect and isolate at different working stages, avoiding interference from ambient air, water vapor, and residual volatile organic compounds on the adsorbent bed. It also allows for effective purging of the adsorption tube and related pipelines during cleaning and regeneration, thereby reducing baseline drift and improving stability and reliability during multiple cycle detection processes.

[0084] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A portable gas chromatograph integrating cryogenic enrichment-thermal desorption pretreatment, comprising an instrument housing and a chromatographic separation unit and a detection unit disposed within the instrument housing, characterized in that, Also includes: The gas delivery and multi-condition gas path control unit is used to introduce ambient gas, carrier gas and cleaning gas and switch the gas path status. The integrated pretreatment unit for cryogenic enrichment and thermal desorption includes a staged temperature-controlled cryogenic enrichment component and a micro-tube thermal desorption component. The graded temperature-controlled cryogenic enrichment component includes an inner active cooling subunit and an outer thermal isolation temperature control subunit. The inner active cooling subunit is used to cool the micro-adsorption tube, and the thermal isolation temperature control subunit is disposed between the micro-adsorption tube and the external environment. The microtubular thermal desorption assembly includes the micro-adsorption tube and a heating unit, wherein the heating unit is fitted to the outer wall of the micro-adsorption tube.

2. The portable gas chromatograph according to claim 1, characterized in that, The gas delivery and multi-condition gas path control unit includes a sampling and gas supply control subunit and a multi-condition gas path switching subunit. The sampling and gas supply control subunit includes an ambient gas inlet, a carrier gas inlet, a cleaning gas inlet, multiple solenoid valves, an electric six-way valve, a mass flow meter, and a diaphragm sampling pump. The multi-condition gas path switching subunit is arranged around the integrated pretreatment unit for cryogenic enrichment and thermal desorption. The multi-condition gas path switching subunit includes an enrichment main gas path submodule, an enrichment bypass submodule, and a cleaning gas path submodule. The enrichment bypass submodule is arranged in parallel with the enrichment main gas path submodule.

3. The portable gas chromatograph according to claim 1, characterized in that, The inner active cooling subunit includes a semiconductor cooling chip. The cold end of the semiconductor cooling chip is in contact with the micro-adsorption tube through a high thermal conductivity connector. The hot end of the semiconductor cooling chip is thermally coupled to a heat dissipation system consisting of a heat sink and a fan.

4. The portable gas chromatograph according to claim 1, characterized in that, The thermal insulation and temperature control subunit is an aerogel insulation layer covering the outer periphery of the micro-adsorption tube.

5. The portable gas chromatograph according to claim 1, characterized in that, The thermal isolation temperature control subunit is a sealed outer shell disposed around the micro-adsorption tube, and a closed gas thermal insulation cavity is formed between the outer shell and the micro-adsorption tube.

6. The portable gas chromatograph according to claim 1, characterized in that, The microtubular thermal desorption assembly further includes a temperature detection unit, which includes a first temperature sensor disposed inside the micro-adsorption tube or in the vicinity of the adsorbent bed, and a second temperature sensor disposed on the outer wall of the micro-adsorption tube.

7. The portable gas chromatograph according to claim 2, characterized in that, The enrichment bypass submodule includes a micro quartz tube, which has the same specifications as the micro adsorption tube and is not filled with adsorbent. In non-enrichment conditions or standby mode, the solenoid valve corresponding to the enrichment bypass submodule is opened and the solenoid valve corresponding to the enrichment main gas path is closed, so that the gas flow passes through the micro quartz tube without entering the micro adsorption tube.

8. The portable gas chromatograph according to claim 2, characterized in that, The cleaning gas circuit module is connected to the micro-adsorption tube via an independently configured cleaning solenoid valve. During the cleaning and regeneration process, the cleaning solenoid valve is opened, and the cleaning gas enters the adsorbent bed from the outlet end of the micro-adsorption tube in the reverse direction.

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