A portable gas chromatograph for separating volatile organic compounds

Abstract

The application discloses a portable gas chromatograph for volatile organic compound separation, and relates to the field of volatile organic compound separation.The gas chromatograph comprises a thermal desorption module, a gas chromatograph module and a detection module, the thermal desorption module is connected with the gas chromatograph module through a gas circuit, and the gas chromatograph module is connected with the detection module through a gas circuit.The thermal desorption module comprises an adsorption tube and a ring-shaped heating element, the ring-shaped heating element is nested outside the adsorption tube, and is used for desorbing analytes in adsorption material.The gas chromatograph module comprises a chromatographic column, a heating rod, a cooling device and a column oven, the chromatographic column, the heating rod and the cooling device are arranged in the column oven, and are used for resolving analytes from a stationary phase.The detection module is used for detecting separated substances.The application integrates the thermal desorption module, the gas chromatograph separation module and the detection module, and has the advantages of compact structure, small volume, light weight and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of volatile organic compound separation, and in particular to a portable gas chromatograph for separating volatile organic compounds. BACKGROUND

[0002] The detection and management of volatile organic compounds (VOCs) is crucial for improving air quality and protecting public health. Therefore, accurate detection and management of VOCs is a key measure to reduce environmental pollution and improve human life quality. However, the existing VOCs detection technology, although having advantages in detection limit and accuracy, still has many limitations, especially in cost, convenience, etc., which limits its application in large-scale environmental monitoring.

[0003] The traditional gas chromatograph combined with different detectors to analyze VOCs is the most commonly used technology, which is often regarded as the gold standard for analyzing VOCs due to its high sensitivity, good reproducibility, and stable performance. For example, the standard technical specification 5030C / 8260B in the prior art is a mature analysis method for VOCs quantification. This method requires collecting samples into a tank, and then taking them into the laboratory for analysis using a gas chromatograph combined with different detectors. However, the wide application of this technology is limited by many factors, including purchase cost, operation complexity, and analysis time. In addition, the weight and volume of the instrument itself greatly reduce the portability of the instrument, limiting its large-scale layout in field observations. Proton transfer reaction mass spectrometry can be used for rapid online detection of VOCs, which has the characteristics of no need for pre-concentration, direct sampling, rapid response, soft chemical ionization, and high sensitivity, with a detection limit of trillionth order. However, it also has some disadvantages, such as inconsistent ionization efficiency. The ionization efficiency may vary with the properties of different compounds in the sample, which may need to be calibrated or corrected in quantitative analysis.

[0004] Portable gas chromatographs (p-GC) have the advantages of low cost, small size, portability, etc., and can detect low concentration (ppbv to sub-ppbv level) VOCs in real time, providing important support for analyzing the source and spatial and temporal distribution characteristics of VOCs in the atmosphere. Therefore, it is of great significance to develop a portable gas chromatograph that is convenient, economical, and highly sensitive for real-time detection of volatile organic compounds in the field of volatile organic compound detection. SUMMARY

[0005] The technical problem solved by the present application is that, in the field of volatile organic compound separation, although traditional gas chromatographs have high detection accuracy, they have defects such as high cost, large size and complex operation, and need to be completed in a laboratory environment, which cannot meet the needs of real-time monitoring in the field. Although proton transfer reaction mass spectrometry has a fast response, the inconsistent ionization efficiency leads to frequent calibration for quantification, which affects accuracy. Although existing portable devices have a certain portability, there are still deficiencies in core links such as stability of adsorption materials, response speed of temperature control systems and chromatographic separation efficiency, such as short adsorption tube breakthrough time, limited heating and cooling rate of the column oven, and difficulty in balancing detection sensitivity and analysis timeliness.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a portable gas chromatograph for volatile organic compound separation, comprising a thermal desorption module, a gas chromatograph module and a detection module, the thermal desorption module being connected to the gas chromatograph module through a gas circuit, and the gas chromatograph module being connected to the detection module through a gas circuit.

[0008] The thermal desorption module comprises an adsorption tube and a ring-shaped heating element, the ring-shaped heating element being nested outside the adsorption tube, for desorbing analytes in the adsorption material.

[0009] The gas chromatograph module comprises a chromatographic column, a heating rod, a cooling device and a column oven, the chromatographic column, the heating rod and the cooling device being arranged in the column oven, for resolving analytes from a stationary phase.

[0010] The detection module is used for detecting volatile organic compounds separated by the gas chromatograph module.

[0011] In an implementation manner, the adsorption tube is provided with a filling material at both ends and an adsorption material in the middle.

[0012] In an implementation manner, the adsorption tube is a stainless steel tube, the filling material is glass wool, and the adsorption material is Carbograph 5TD, Carbograph 1TD or Tenax TA.

[0013] In an implementation manner, the outer diameter of the adsorption tube is 4-6mm, the length is 30-50mm, the filling material at both ends of the adsorption tube is 15-25mg of glass wool respectively, and the adsorption material is 25-35mg.

[0014] In an implementation manner, the ring-shaped heating element is a ring-shaped high-temperature ceramic heating element, the inner diameter of the ring-shaped high-temperature ceramic heating element is 4-6mm, the length is 0.8-1.2cm, the power is 5-10W, and the heating temperature is ≥190℃.

[0015] In an implementation manner, the chromatographic column is HP-5MS, and the length of the chromatographic column is 1-10 m.

[0016] In an implementation manner, the column oven is a nested double-layer column oven, and heat insulation cotton is arranged between the inner layer and the outer layer, the heating rod is arranged on the surface of the inner layer of the column oven through insulation ceramic and is not in contact with the surface of the inner layer of the column oven, the diameter of the heating rod is 15-17 mm, and the length of the heating rod is 450-460 mm.

[0017] In an implementation manner, the cooling device is arranged at the center of the surface of the inner layer of the column oven, and the chromatographic column is cooled through horizontal blowing.

[0018] In an implementation manner, the column oven is further provided with a K-type thermocouple and a temperature controller, the K-type thermocouple and the temperature controller are electrically connected, the temperature in the column oven is monitored in real time, and a temperature signal is transmitted to the temperature controller, and the temperature controller controls the temperature of the column oven through the heating rod.

[0019] In an implementation manner, the detection module is a photo-ionization detector, and the volume of the gas chromatograph module is ≤0.01 and the mass is ≤5 kg.

[0020] Beneficial effects: The application discloses a portable gas chromatograph for volatile organic compound separation, relates to the field of volatile organic compound separation, and comprises a thermal desorption module, a gas chromatograph module and a detection module, the thermal desorption module is connected with the gas chromatograph module through a gas circuit, and the gas chromatograph module is connected with the detection module through a gas circuit; the thermal desorption module comprises an adsorption tube and a ring-shaped heating element, the ring-shaped heating element is nested outside the adsorption tube, and is used for desorbing analytes in adsorption material; the gas chromatograph module comprises a chromatographic column, a heating rod, a cooling device and a column oven, the chromatographic column, the heating rod and the cooling device are arranged in the column oven, and are used for resolving analytes from a stationary phase; and the detection module is used for detecting separated substances. The thermal desorption module, the gas chromatograph separation module and the detection module are integrated, the structure is compact, the volume is small, and the weight is light, rapid detection and efficient separation of volatile organic compounds are realized. The thermal desorption module adopts an optimized adsorption tube design, the adsorption efficiency and resolution stability of VOCs are improved. The gas chromatograph module combines a temperature control system composed of the heating rod, the cooling device and the column oven, rapid heating and efficient cooling are realized, and the stability of separation performance is ensured. In addition, the heating and cooling system of the gas chromatograph column is further optimized by arranging a K-type thermocouple and a temperature controller, the temperature control precision is improved, and the temperature gradient effect in chromatographic analysis is reduced. The detection module realizes rapid detection of substances. The application can be widely applied to environmental monitoring, industrial emission detection and on-site emergency analysis, and provides an efficient and portable solution for rapid and accurate detection of VOCs. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The structure schematic diagram of each module in the portable gas chromatograph for volatile organic compound separation provided by the embodiment of the application is shown.

[0022] Figure 2 The design size diagram of the thermal desorption module provided by the embodiment of the application is shown.

[0023] Figure 3 The column oven top view and side view of the gas chromatograph module provided by the embodiment of the application are shown.

[0024] Figure 4 The breakthrough time diagram of the thermal desorption module provided by the embodiment of the application is shown.

[0025] Figure 5 The temperature rising test result diagram of the gas chromatograph module provided by the embodiment of the application is shown.

[0026] Figure 6 The temperature falling test result diagram of the gas chromatograph module provided by the embodiment of the application is shown.

[0027] Figure 7A tail flow rate versus column head pressure relationship graph for a chromatographic column of a gas chromatography module is provided by embodiments of the present invention.

[0028] Figure 8 A Gaussian fitting result graph for isoprene chromatographic peaks formed by a gas chromatography module is provided by embodiments of the present invention.

[0029] 101. annular ceramic heating resistor; 102. wire mesh; 103. stainless steel tube; 104. glass wool; 105. adsorbent material; 201. double-layer column oven; 202. heat insulation cotton; 203. heating rod; 204. chromatographic column; 205. fan; 300. photoionization detector; 401. first gas path connection; 402. second gas path connection. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions and effects of the present invention clearer and more explicit, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the present invention.

[0031] The flowchart shown in the drawings is only an example and does not necessarily include all contents and operations or steps, nor does it necessarily execute in the order described. For example, some operations or steps can be further divided, combined or partially merged, so the actual execution order can be changed according to the actual situation.

[0032] It should be understood that the terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present invention specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0033] It should be understood that, in order to facilitate the clear description of the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, the terms "first", "second" and the like are used to distinguish the same or similar items with basically the same function and effect. For example, the first control information and the second control information are only used to distinguish different control information and do not limit the order.

[0034] Those skilled in the art can understand that the terms "first", "second" and the like do not limit the quantity and execution order, and the terms "first", "second" and the like do not necessarily mean different.

[0035] It should also be understood that the term "and / or" used in the present invention specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0036] Monitoring and management of volatile organic compounds (VOCs) is crucial for improving air quality and protecting public health. Therefore, accurate monitoring and management of VOCs is a key measure to reduce environmental pollution and improve human life quality. However, existing VOCs detection technologies, although having advantages in detection limit and accuracy, still have many limitations, especially in cost, convenience, etc., which limit their application in large-scale environmental monitoring.

[0037] Traditional gas chromatographs combined with different detectors for analyzing VOCs are the most commonly used technology, as they have high sensitivity, good reproducibility, and stable performance, and are often considered as the gold standard for analyzing VOCs. For example, the standard technical specification 5030C / 8260B in the prior art is a mature analysis method for VOCs quantification. This method requires collecting samples into a tank, then bringing them into the laboratory for analysis using GC combined with different detectors. However, the wide application of this technology is limited by many factors, including purchase cost, operation complexity, and analysis time, etc. In addition, the weight and volume of the instrument itself greatly reduce the portability of the instrument, limiting its large-scale layout in field observation. Proton transfer reaction mass spectrometry can be used for rapid online detection of VOCs, which has the characteristics of no need for pre-concentration, direct sampling, fast response, soft chemical ionization, and high sensitivity, with a detection limit of trillionth order. However, it also has some disadvantages, such as inconsistent ionization efficiency. The ionization efficiency may vary with the properties of different compounds in the sample, which may need to be calibrated or corrected in quantitative analysis.

[0038] Portable gas chromatographs have the advantages of low cost, small size, and high portability, and can detect low concentration (ppbv to sub-ppbv level) VOCs in real time, providing important support for analyzing the source and spatial and temporal distribution characteristics of VOCs in the atmosphere. Therefore, it is of great significance to develop a convenient, economical, and high-sensitivity gas chromatograph for real-time detection of volatile organic compounds in the field of volatile organic compound detection.

[0039] Overall, in the field of volatile organic compound separation and detection technology, although traditional gas chromatographs have high detection accuracy, they have defects such as high cost, large size, and complex operation, and need to be completed in a laboratory environment, which cannot meet the needs of real-time monitoring in the field. Proton transfer reaction mass spectrometry has fast response, but the inconsistent ionization efficiency leads to frequent calibration for quantification, affecting accuracy. Existing portable devices have certain portability, but still have deficiencies in core aspects such as stability of adsorption material, response speed of temperature control system, and efficiency of chromatographic separation, such as short adsorption tube breakthrough time, limited column oven heating and cooling rate, and difficulty in balancing detection sensitivity and analysis timeliness. A portable gas chromatograph with high-efficiency separation and accurate detection capability is urgently needed to realize real-time detection of volatile organic compounds.

[0040] The embodiment provides a portable gas chromatograph for separating and detecting volatile organic compounds, which comprises a thermal desorption module, a gas chromatograph module and a detection module, the thermal desorption module is connected with the gas chromatograph module through a gas path, and the gas chromatograph module is connected with the detection module through a gas path.

[0041] The thermal desorption module comprises an adsorption tube and a ring-shaped heating element, the ring-shaped heating element is nested outside the adsorption tube, and is used for desorbing analytes in adsorption material.

[0042] The gas chromatograph module comprises a chromatographic column, a heating rod, a cooling device and a column oven, the chromatographic column, the heating rod and the cooling device are arranged in the column oven, and are used for resolving analytes from a stationary phase.

[0043] The detection module is used for detecting volatile organic compounds separated by the gas chromatograph module.

[0044] In the embodiment, as shown in Figure 1 The gas chromatograph integrates the thermal desorption module, the gas chromatograph separation module and the photoionization detector 300, so that rapid detection and efficient separation of VOCs are realized. The thermal desorption module is provided with an adsorption tube and is filled with high-performance adsorption material 105, and is combined with a ring-shaped heating element to realize efficient resolution and accurate control. The thermal desorption module is responsible for the adsorption, enrichment and resolution of volatile organic compounds, that is, desorption. That is, the adsorption tube filled with adsorption material 105 captures VOCs in the sample, and the ring-shaped heating element uniformly heats the adsorption tube, so that the VOCs are desorbed and released from the adsorption material 105 to form a high-concentration analyte gas. The gas chromatograph module is provided with a chromatographic column 204, and is combined with a heating rod 203, an air cooling system and a column oven to realize rapid heating and efficient cooling, improve the stability and accuracy of chromatographic separation. Different components are separated through the action of the stationary phase of the chromatographic column 204, and the heating rod 203 and the cooling device are used to realize rapid heating and cooling of the column oven, so as to ensure the separation efficiency, and finally complete quantitative analysis through the detection module. The cooling device can be a fan 205, which cools the column oven by air cooling. The photoionization detector 300 is used for detecting the separated substances.

[0045] In one implementation manner, the adsorption tube is provided with filling material at both ends and is provided with adsorption material 105 in the middle.

[0046] In the embodiment, as shown in Figure 2As shown in the thermal desorption module, the manufacturing process of the adsorption tube includes setting the filler material at one end of the tube, then adding the adsorption material 105 in the middle, and then setting the filler material at the other end to prevent material leakage. This design aims to ensure that the adsorption material 105 is fixed and prevents it from moving or leaking during use, thereby improving adsorption efficiency and stability.

[0047] In one implementation, the adsorption tube is a stainless steel tube 103, the filler material is glass wool 104 and wire mesh 102, and the adsorption material 105 is Carbograph 5TD, Carbograph 1TD or Tenax TA.

[0048] In this embodiment, the filler material can be selected as glass wool 104. The reason for choosing glass wool 104 as the filler material is that it has excellent high-temperature resistance and can maintain its structural integrity under high-temperature conditions, ensuring reliability and durability during thermal desorption. In addition, the adsorption tube can be selected as a stainless steel tube 103, and the adsorption material 105 can be selected as Carbograph 5TD, Carbograph 1TD or Tenax TA. Carbograph 5TD and Carbograph 1TD are adsorbents of graphitized carbon black, and Tenax TA is a high-molecular linear polymer commonly used as an adsorbent. The use of a stainless steel adsorption tube, filled with adsorption material 105 and fixed with glass wool 104, ensures efficient adsorption and stability.

[0049] In one implementation, the adsorption tube has an outer diameter of 4-6mm and a length of 30-50mm, and the filler material at both ends of the adsorption tube is 15-25mg of glass wool 104, and the adsorption material 105 is 25-35mg.

[0050] In this embodiment, the adsorption tube has an outer diameter of 4-6mm and a length of 30-50mm, and the filler material at both ends of the adsorption tube is 15-25mg of glass wool 104, and the adsorption material 105 is 25-35mg. As Figure 2 As shown in the thermal desorption module, the adsorption tube is a stainless steel tube 103 with an outer diameter of 5mm and a length of 40mm, one end of the adsorption tube is filled with 20mg of glass wool 104, the middle is filled with 30mg of adsorption material 105, and the other end is filled with 20mg of glass wool 104.

[0051] In one implementation, the ring-shaped heating element is a ring-shaped high-temperature ceramic heating element, the ring-shaped high-temperature ceramic heating element has an inner diameter of 4-6mm, a length of 0.8-1.2cm, a power of 5-10W, and a heating temperature ≥190℃.

[0052] In this embodiment, in order to realize efficient heating of the thermal desorption process, a ring-shaped high-temperature ceramic heating element is used, which is a ring-shaped ceramic heating resistor 101. The inner diameter of the ring-shaped high-temperature ceramic heating element is 4-6 mm, the length is 0.8-1.2 cm, and the power is 5-10 W. Among them, the inner diameter of the ceramic heating element is 5 mm, the length is 1 cm, and the power is 7 W, which can provide a heating temperature of up to 190°C. This heating element ensures that the adsorption tube can be uniformly heated during the desorption process, promoting the desorption of analytes in the adsorption material 105. Through the ring-shaped high-temperature ceramic heating element in the self-designed thermal desorption module, the adsorption tube can be uniformly heated at high temperature, improving the desorption efficiency and ensuring the efficient release of VOCs.

[0053] After the adsorption tube is completed, the breakthrough time of the adsorption tube needs to be tested first to evaluate its performance and stability in actual application.

[0054] In this embodiment, Carbograph 5TD is selected as the adsorption material 105 of the adsorption tube, and the breakthrough time of the adsorption tube is as shown in Figure 4 The abscissa in the figure represents the time of continuously injecting benzene into the adsorption tube, and the ordinate represents the response signal intensity of the detection module. According to the experimental results, when the signal value remains at the baseline level, it indicates that the gas has not penetrated the adsorption tube, and when the response signal increases significantly, it indicates that the adsorption tube has started to penetrate and release gas. From the figure, it can be observed that the breakthrough time of Carbograph 5TD is about 10 h.

[0055] In an implementation manner, the chromatographic column 204 is HP-5MS, and the length of the chromatographic column 204 is 1-10 m.

[0056] The chromatographic column 204 can be Agilent HP-5MS. After the analyte enters the chromatographic column 204, it interacts with the stationary phase in the chromatographic column 204, and the analyte is resolved from the stationary phase by heating the chromatographic column 204. In order to explore the influence of the length of the gas chromatographic column 204 on the head pressure and outlet flow rate, the relationship between the head pressure and outlet flow rate of gas chromatographic columns 204 of different lengths is tested, as shown in Figure 7The experimental results show that, with the increase of the length of the chromatographic column 204, the relationship between the inlet pressure and the outlet flow rate shows obvious regularity. For a 1m long chromatographic column 204, when the outlet flow rate is 1mL / min, the inlet pressure is 0.005MPa; with the increase of the outlet flow rate to 5mL / min, the inlet pressure rises to 0.021MPa. For a 5m long chromatographic column 204, when the outlet flow rate is 1mL / min, the inlet pressure is 0.040MPa, and when the flow rate increases to 5mL / min, the inlet pressure rises to 0.081MPa. Similarly, for a 10m long chromatographic column 204, when the outlet flow rate is 1mL / min, the inlet pressure is 0.060MPa, and when the flow rate increases to 5mL / min, the inlet pressure further rises to 0.130MPa. The results clearly show a trend that for each column length, the increase of the outlet flow rate will cause the inlet pressure to increase proportionally. Moreover, with the increase of the column length, the pressure rise is more significant. This can be attributed to the fact that the carrier gas encounters greater resistance when passing through a longer chromatographic column 204, resulting in higher pressure at the inlet under a given flow rate. By analyzing the relationship between the length of the chromatographic column 204 and the inlet pressure, the outlet flow rate, the column length is optimized to achieve better separation effect and improve detection accuracy.

[0057] In an implementation manner, the column oven is a nested double-layer column oven 201, and heat insulation cotton 202 is arranged between the inner layer and the outer layer, the heating rod 203 is arranged on the surface of the inner layer of the column oven through insulating ceramic and does not contact the surface of the inner layer of the column oven, and the diameter of the heating rod 203 is 15-17mm and the length is 450-460mm.

[0058] In the embodiment, in order to heat the chromatographic column 204, a heating rod 203 is used to heat the chromatographic column 204, and the diameter of the heating rod 203 is 15-17mm and the length is 450-460mm. The diameter of the heating rod 203 is 16mm, the length is 455mm, and the working voltage is 220V. The heating rod 203 realizes the heating function by applying voltage. In the design, in order to prevent the heating rod 203 from contacting the wall of the column oven, the heating rod 203 is supported by insulating ceramic, and the heating rod 203 is fixed at the bottom of the column oven through the support of the insulating ceramic. In addition, in order to reduce the loss of heat in the heating process, a double-layer column oven 201 is used for heat preservation. The specific heat preservation measures include nesting the double-layer column oven 201, filling heat insulation cotton 202 between the two layers, and fixing the structure of the double-layer column oven 201 by using screws to improve the heat preservation effect.

[0059] In an implementation manner, the cooling device is arranged at the center of the inner surface of the column oven, and the chromatographic column 204 is cooled by horizontal blowing.

[0060] In this embodiment, in order to provide effective heat dissipation when the chromatographic column 204 needs to be cooled, the air cooling mode is selected. The cooling device can be a fan 205 installed at the bottom of the column oven, which realizes the cooling of the chromatographic column 204 by horizontal blowing.

[0061] In an implementation manner, a K-type thermocouple and a temperature controller are further arranged in the column oven, and the K-type thermocouple and the temperature controller are electrically connected, for monitoring the temperature in the column oven in real time and transmitting a temperature signal to the temperature controller, and the temperature controller controls the temperature of the column oven through the heating rod 203.

[0062] In this embodiment, in order to accurately control the temperature, a K-type thermocouple is used to monitor the temperature of the chromatographic column 204 in real time, and the voltage applied to the heating wire is adjusted by the temperature controller to ensure the stability of the temperature. The thermocouple, the heating rod 203, the column oven and the cooling device form a closed-loop temperature control system in the gas chromatography module of the portable gas chromatograph, and realize the accurate control and rapid response of the temperature of the chromatographic column 204 through the combined working mode of real-time monitoring, dynamic adjustment and structural cooperation. Among them, the K-type thermocouple is used for real-time temperature monitoring and provides a feedback signal, the heating rod 203 is used as a heating source for the chromatographic column 204, which converts electrical energy into heat energy, the column oven is used to accommodate the chromatographic column 204 and maintain the temperature environment, and has the functions of heat preservation and heat dissipation, and the cooling device is used for forced convection heat dissipation to realize rapid cooling.

[0063] In the heating stage, after receiving the heating instruction, the temperature controller applies full-power voltage to the heating rod 203 to heat it at the maximum rate. The heating rod 203 is isolated from the bottom of the column oven by an insulating ceramic support to avoid contact heat dissipation, so as to ensure that the heat is concentrated on the chromatographic column 204, and the double-layer structure of the column oven and the heat insulation cotton 202 reduce the heat loss and reduce the energy consumption of the heating rod 203. The thermocouple continuously monitors the temperature in the column oven, and when the temperature reaches the set value, the temperature controller switches to the adjustment mode to gradually reduce the voltage of the heating rod 203 and stabilize the heating rate. In the temperature maintaining stage, when the temperature reaches the set value, the temperature controller enters the adjustment mode to maintain the temperature fluctuation within a certain range. The thermocouple data is used as a feedback signal to adjust the duty cycle of the heating rod 203 in real time. In the cooling stage, if the cooling device is a fan 205, the heating rod 203 is powered off and the fan 205 is started at full speed. Specifically, after receiving the cooling instruction, the temperature controller cuts off the power supply of the heating rod 203, and the fan 205 runs at a set power to blow the chromatographic column 204 through horizontal airflow to accelerate heat exchange. The airflow path generated by the fan 205 is designed to be inhaled at the bottom, horizontally swept over the chromatographic column 204, and discharged at the top to ensure the uniformity of the cooling.

[0064] To evaluate the temperature control performance of the column oven, the heating process of the gas chromatography module was tested. In the experiment, the column oven door remained closed, and the heating rod 203 was powered to heat up, thereby heating the column oven. The temperature change was monitored in real time by the thermocouple to ensure accurate recording of the temperature inside the oven. During the heating process, the fan 205 was powered on to promote uniform temperature distribution inside the column oven by forced air flow, to avoid temperature gradients or local overheating. The experiment was repeated three times to ensure the reliability and consistency of the data. The results, as shown in Figure 5 , show that the column oven can raise the temperature from 30°C to 70°C within 120s, with a maximum heating rate of 20°C / min, demonstrating its high heating efficiency. In addition, the temperature can be maintained stable after reaching the set value, indicating that the module has excellent heating performance and good temperature control stability, and can provide an accurate and stable operating environment for experiments.

[0065] To comprehensively evaluate the temperature control performance of the module, the cooling performance of the gas chromatography module was also tested in detail. During the test, the column oven door remained open, and the power to the heating rod 203 was first turned off to stop the heating process, while the fan 205 continued to operate to accelerate cooling using air flow. To ensure the accuracy of temperature changes, the experiment monitored the temperature inside the column oven in real time by the thermocouple. In this experiment, to ensure the reliability and consistency of the data, the test was repeated three times, and all experimental conditions remained constant. The experimental results, as shown in Figure 6 , show that under this setting, the temperature of the column oven can be quickly reduced from 100°C to 40°C within 120s, achieving a cooling rate of up to 30°C / min. This indicates that the module not only has high heating capacity, but also can achieve rapid temperature drop in a short time, and can provide a fast-responding temperature control system for experiments, meeting the high requirements for accurate temperature control during experiments.

[0066] In one implementation, the detection module is a photoionization detector 300, and the volume of the gas chromatography module is ≤0.01 and the mass is ≤5kg.

[0067] In this embodiment, to ensure the overall size and weight of the gas chromatograph, the volume of the gas chromatography module is limited to within 0.01 , and the mass is limited to within 5kg. The overall device of the gas chromatography module is as shown in Figure 3 , with a volume of 0.007 and a mass of 3.5kg. The gas chromatography module adopts a compact design, making the device small in size and light in weight, suitable for on-site rapid detection. Compared with traditional large-scale GCs in laboratories, it has the advantages of portability and low cost. The detection module uses a photoionization detector 300 for detecting separated substances.

[0068] The experiment was carried out at a column tail flow rate of 8 mL / min, and 2 μL of isoprene was injected each time. The obtained chromatographic data was fitted using an exponential correction Gaussian distribution, as shown in Figure 8 The experimental results show that the half peak width (full width at half maximum) is 2.9 min at a flow rate of 8 mL / min.

[0069] The portable gas chromatograph of the embodiment adopts a compact design, so that the device is small in size and light in weight, and is suitable for on-site rapid detection. Compared with traditional laboratory large GC, the portable gas chromatograph has the advantages of portability and low cost. At the same time, the gas chromatograph integrates a thermal desorption module. The self-designed thermal desorption module adopts a ring-shaped high-temperature ceramic heating element, which can uniformly heat the adsorption tube at high temperature, improve the desorption efficiency, and ensure the efficient release of VOCs. On this basis, by optimizing the structure and material selection of the adsorption tube, specifically using a stainless steel adsorption tube, filling Carbograph 5TD, Carbograph 1TD or Tenax TA adsorption material 105, and fixing with glass wool 104, the high-efficiency adsorption and stability are ensured. Further, the performance of the adsorption material 105 is verified by a breakthrough experiment, the optimal adsorption material 105 for different VOCs is determined, and the detection sensitivity is optimized. For temperature control of the gas chromatograph module, specifically, a heating rod 203 is used for column 204 temperature rise, combined with a K-type thermocouple and a temperature control system for precise temperature control, to ensure the stability of separation, and at the same time, a double-layer column oven 201 and a wind cooling system are used for efficient heat dissipation, with a cooling rate of 30℃ / min, to ensure rapid response. Finally, the inlet pressure of the column 204 is also optimized. Specifically, by analyzing the relationship between the column 204 length and the inlet pressure, outlet flow rate through experiments, the column length selection is optimized, better separation effect is achieved, and the detection accuracy is improved.

[0070] In summary, the application discloses a portable gas chromatograph for volatile organic compound separation, and relates to the field of volatile organic compound separation and detection, and comprises a thermal desorption module and a gas chromatograph module; the thermal desorption module comprises an adsorption tube and a ring-shaped heating element, the ring-shaped heating element is nested outside the adsorption tube, and is used for desorbing analytes in the adsorption material 105; the gas chromatograph module comprises a chromatographic column 204, a heating rod 203, a cooling device and a column oven, the chromatographic column 204, the heating rod 203 and the cooling device are arranged in the column oven, and are used for resolving analytes from a stationary phase. The application integrates the thermal desorption module and the gas chromatograph separation module, has compact structure, small volume and light weight, realizes rapid detection and efficient separation of volatile organic compounds. The optimized adsorption tube design improves the adsorption efficiency and resolution stability of VOCs, and in combination with a high-precision temperature control system, rapid heating and efficient cooling are realized, so that the stability of the separation performance is ensured. Further, the heating and air cooling system of the gas chromatograph column 204 is optimized, the temperature control precision is improved, and the temperature gradient effect in chromatographic analysis is reduced. The application can be widely applied to environmental monitoring, industrial emission detection and on-site emergency analysis, and provides an efficient and portable solution for rapid and accurate detection of VOCs.

[0071] The technical features of the above embodiments can be combined in any manner, and to make the description concise, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present application.

[0072] The above-described embodiments only express several implementation manners of the application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the application, and these all belong to the protection scope of the application. Therefore, the protection scope of the application should be subject to the appended claims.

Claims

1. A portable gas chromatograph for separating volatile organic compounds, characterized by, The thermal desorption module, the gas chromatography module and the detection module are connected through gas paths; The thermal desorption module comprises an adsorption tube and a ring-shaped heating element, the ring-shaped heating element is nested outside the adsorption tube, and is used for desorbing analytes in the adsorption material; both ends of the adsorption tube are provided with filling materials, and the middle of the adsorption tube is provided with adsorption material; the adsorption tube is a stainless steel tube, the filling materials are glass wool and iron wire mesh, and the adsorption material is Carbograph 5TD, Carbograph 1TD or Tenax TA; The gas chromatography module comprises a chromatographic column, a heating rod, a cooling device and a column oven, the chromatographic column, the heating rod and the cooling device are arranged in the column oven, and are used for resolving analytes from a stationary phase; the column oven is a nested double-layer column oven, and is provided with heat insulation cotton between the inner layer and the outer layer; the heating rod is arranged on the surface of the inner layer of the column oven through insulating ceramic, and does not contact the surface of the inner layer of the column oven; the diameter of the heating rod is 15-17 mm, and the length is 450-460 mm; the cooling device is arranged on the central surface of the inner layer of the column oven, and cools the chromatographic column through horizontal blowing; The detection module is used for detecting volatile organic compounds separated by the gas chromatography module.

2. The portable gas chromatograph for separating volatile organic matters according to claim 1, wherein The outer diameter of the adsorption tube is 4-6 mm, and the length is 30-50 mm; the filling materials at both ends of the adsorption tube are respectively 15-25 mg of glass wool; and the mass of the adsorption material is 25-35 mg.

3. The portable gas chromatograph for separating volatile organic matters according to claim 1, wherein, The ring-shaped heating element is a ring-shaped high-temperature ceramic heating element, the inner diameter of the ring-shaped high-temperature ceramic heating element is 4-6 mm, the length is 0.8-1.2 cm, the power is 5-10 W, and the heating temperature is greater than or equal to 190 DEG C.

4. The portable gas chromatograph for separating volatile organic matters according to claim 1, wherein The chromatographic column is HP-5MS, and the length of the chromatographic column is 1-10 m.

5. The portable gas chromatograph for separating volatile organic matters according to claim 1, wherein, The column oven is further provided with a K-type thermocouple and a temperature controller, the K-type thermocouple and the temperature controller are electrically connected, are used for monitoring the temperature in the column oven in real time, and transmit a temperature signal to the temperature controller; and the temperature controller controls the temperature of the column oven through the heating rod.

6. The portable gas chromatograph for separating volatile organic compounds according to claim 1, wherein The detection module is a photo-ionization detector, the volume of the gas chromatograph module is ≤0.01 and the mass is ≤5 kg.

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