A method and device for the pre-treatment of volatile organic compounds in soil by purge and trap

Abstract

The present application relates to the technical field of environment detection, and discloses a purging and trapping pretreatment method and device for detecting volatile organic compounds in soil, which comprises the following steps: S1, weighing a quantitative soil sample and placing it in a purging bottle, driving the top assembly to move downward by a pushing device, covering the purging bottle, then adding a quantitative blank reagent water through a sample injection needle, then stirring to uniformly disperse the sample to form a mud slurry; S2, starting a heating device to control the temperature of the purging bottle, and bubbling and purging the mud slurry with inert gas under constant temperature conditions, so that the volatile organic compounds in the mud slurry escape with the carrier gas; S3, the escaped gas enters a detection device through a gas outlet pipe, is dried and purged in the detection device to remove water, then is heated for desorption, and finally is introduced into a gas chromatography system for detection; in S1, the mass-volume ratio of the soil sample to the blank reagent water is 1:1-1:3, the stirring and mixing time is 8-15 min, and the soil particles are completely dispersed in the mud slurry after stirring.

Description

Technical Field

[0001] This invention relates to the field of environmental monitoring technology, specifically to a purge-and-trap pretreatment method and apparatus for detecting volatile organic compounds in soil. Background Technology

[0002] The detection of volatile organic compounds in soil and groundwater is an important part of environmental monitoring. Taking isopropanol as an example, it is an organic solvent widely used in the pharmaceutical, chemical and electronic cleaning industries. Due to its strong water solubility and volatility, it has become a key focus in environmental risk assessment. At present, for the pretreatment of soil, the mainstream technologies mostly adopt headspace or purge-and-trap methods, which aim to separate and enrich the target substances from the solid matrix for gas chromatography analysis.

[0003] Patent application CN202510572418.8 discloses a purge and trap device and a purge and trap method, including a base plate, a shell, a feeding robotic arm, a purge device, a lifting platform, and a sample delivery device. This invention solves the following problems existing in the prior art during sample purge and trapping: the inability to appropriately limit sample vials of different diameters, leading to a lack of stability in the sample vials; and the inability to clean the purge needle, resulting in the purge needle carrying residual sample, affecting the analytical purity of subsequent sample purging. This invention can clamp and limit sample vials of different diameters from multiple directions, and can further limit the sample vials by applying forces in opposite directions, thereby ensuring the stability of the sample vials.

[0004] Existing purge-and-trap technologies typically involve directly bubbling the soil solids. However, due to the complex pore structure between soil particles, the airflow tends to form "channels" along the path of least resistance, making it difficult to reach the target material deep within the micropores. This results in low extraction efficiency and poor parallelism. Although current technologies attempt to add a small amount of water for wetting, this only alters the soil surface tension and cannot fundamentally change the physical morphology of the sample, so the channeling effect still exists. Furthermore, for highly water-soluble volatile organic compounds, traditional hydrophobic membrane dehydration causes significant loss of the target material, making water vapor interference from high-proportion water addition a formidable technical obstacle in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a purge-and-trap pretreatment method and apparatus for detecting volatile organic compounds in soil, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a pretreatment method for purge-trap detection of volatile organic compounds in soil, comprising the following steps: S1. Weigh a quantitative amount of soil sample and place it in a purge bottle. Drive the top component down using the pusher to close the purge bottle. Then add a quantitative amount of blank reagent water through the injection needle. Stir to disperse the sample evenly and form a slurry. S2. Start the heating device to maintain a constant temperature for the purge bottle, and under constant temperature conditions, introduce inert gas to purge by bubbling, so that the volatile organic compounds in the mud can escape with the carrier gas. S3. The escaping gas enters the detection device through the outlet pipe, where it is dried and purged to remove moisture. Then, it is heated to desorb and finally introduced into the gas chromatography system for detection.

[0007] According to the above technical solution, in S1, the mass-to-volume ratio of soil sample to blank reagent water is 1:1 to 1:3, the mixing time is 8 to 15 minutes, and the soil particles are completely dispersed in the mud after mixing.

[0008] According to the above technical solution, in S2, the temperature of the constant temperature purging is 40℃~60℃; the inert gas is pure helium or pure nitrogen, the purging gas flow rate is 30~50 mL / min, and the purging time is 8~12 min.

[0009] According to the above technical solution, in S3, the desorption temperature is 180℃~250℃ and the desorption time is 1~4 min; the gas chromatography system uses a weakly polar capillary column for separation, and the stationary phase of the column is a bonded cross-linked weakly polar polysiloxane.

[0010] A purge-trap pretreatment device for detecting volatile organic compounds in soil: a connecting plate is fixedly connected to the top of the pushing device, a top component is fixedly connected to the inner wall of the connecting plate, a central mechanism is fixedly connected to the outer wall of the pushing device, an air supply device is fixedly connected to the rear side of the pushing device, a detection device is fixedly connected to the rear side of the pushing device, an air inlet pipe is fixedly connected to the air outlet of the air supply device, and an air outlet pipe is fixedly connected to the air inlet of the detection device, wherein the front ends of the air inlet pipe and the front ends of the air outlet pipe are both fixedly connected to the top component.

[0011] According to the above technical solution, the central mechanism includes an outer frame, a heating device is fixedly connected to the inner wall of the outer frame, an adjustment component is rotatably connected to the inner wall of the outer frame via a bearing, and a purge bottle is placed on top of the adjustment component.

[0012] According to the above technical solution, the adjustment component includes a motor, the bottom of which is fixedly connected to the outer frame, the output end of which is fixedly connected to a housing, the outer wall of which is rotatably connected to the outer frame via a bearing, a baffle fixedly connected to the top of which has a slot, a push rod fixedly connected to the inner wall of the outer frame, a connecting ring fixedly connected to the top of the push rod, a rotating ring rotatably connected to the top of the connecting ring via a bearing, and a fixing component fixedly connected to the inner wall of the rotating ring.

[0013] According to the above technical solution, the fixing component includes a connecting column, the outer wall of which is fixedly connected to a rotating ring, a U-shaped plate fixedly connected to the top of the connecting column, a connecting head fixedly connected to the inner wall of the U-shaped plate, a first slider fixedly connected to the outer wall of the connecting head, the inner wall of the first slider being movably connected to the outer shell, a connecting rod rotatably connected to the inner wall of the connecting head via a bearing, a second slider rotatably connected to the end of the connecting rod away from the connecting head via a bearing, the outer wall of the second slider being movably connected to a slot, a fixing head fixedly connected to the top of the second slider, and an elastic component fixedly connected to the end of the second slider away from the connecting head, the outer wall of the elastic component being fixedly connected to the outer shell. By setting the top component and utilizing the arc-shaped porous structure of the air outlet plate, the inert gas is evenly distributed through the air ring and the air outlet plate, and then introduced into the mud system in the form of microbubbles at multiple angles along the arc-shaped curved surface. This significantly increases the gas-liquid contact area and micro-disturbance dynamics, significantly improving the purging efficiency and the escape rate of the target volatile organic compounds, ensuring the high efficiency and stability of the purging and collection process.

[0014] According to the above technical solution, the top assembly includes a cover plate, which is fitted onto the top of the purge bottle. An air outlet is fixedly connected to the top of the cover plate, and the top of the air outlet is fixedly connected to an air outlet pipe. An air inlet is fixedly connected to the top of the cover plate, and the top of the air inlet is fixedly connected to an air inlet pipe. A venting ring is fixedly connected to the bottom of the cover plate, and a venting plate is fixedly connected to the bottom of the venting ring. An air outlet plate is fixedly connected to the bottom of the venting plate, and a protruding plate is fixedly connected to the outer wall of the air outlet plate. A liquid inlet is provided on the top of the cover plate, which is used for the insertion of a sampling needle. A polytetrafluoroethylene silicone pad is installed inside the liquid inlet to prevent subsequent air leakage. By setting the top assembly, during the continuous rotation of the purge bottle, the protruding plate acts as a fixed obstacle, generating forced shearing and turbulence on the mud, enhancing the turbulence and mixing uniformity within the mud, allowing soil particles to fully contact the blank reagent water, and accelerating the mass transfer process of volatile organic compounds from the solid phase to the aqueous phase.

[0015] Compared with the prior art, the present invention provides a pretreatment method and apparatus for purge-trap detection of volatile organic compounds in soil, which has the following beneficial effects: 1. This invention transforms heterogeneous soil solids into homogeneous fluid slurry by adding a specific proportion of blank reagent water. This forces the purging gas to pass through the sample in the form of tiny bubbles, greatly increasing the gas-liquid contact area and fundamentally eliminating the channeling effect. This increases the recovery rate of target volatile organic compounds from 60%-70% in dry methods to over 95%.

[0016] 2. This invention employs a polar solvent elution mechanism, which effectively improves detection accuracy. By using water as a polar solvent and based on the principle of "like dissolves like," polar volatile organic compounds can be quickly displaced from the surface of soil particles to the aqueous phase, reducing mass transfer resistance. At the same time, the homogeneity of the mud system is far superior to that of solid soil, effectively reducing sampling deviations caused by uneven soil particle size, and ensuring that the relative standard deviation of parallel samples can be controlled within 5%, which is better than the requirements of existing technical standards.

[0017] 3. By setting up a top component and utilizing an arc-shaped porous structure air outlet plate, the inert gas is evenly distributed through the air ring and air outlet plate, and then introduced into the mud system in the form of microbubbles at multiple angles along the arc-shaped curved surface. This greatly increases the gas-liquid contact area and micro-disturbance dynamics, significantly improves the purging efficiency and the escape rate of the target volatile organic compounds, and ensures the high efficiency and stability of the purging and collection process.

[0018] 4. By setting a top component, the protruding plate acts as a fixed obstacle to exert forced shearing and turbulence on the mud during the continuous rotation of the purge bottle. This enhances the turbulence and mixing uniformity inside the mud, allowing soil particles to fully contact the blank reagent water and accelerating the mass transfer process of volatile organic compounds from the solid phase to the aqueous phase. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the central mechanism of the present invention; Figure 3 This is a cross-sectional view of the central mechanism of the present invention; Figure 4 This is a schematic diagram of the adjustment component of the present invention; Figure 5 This is a cross-sectional view of the adjustment component of the present invention; Figure 6 This is a schematic diagram of the fixing component of the present invention; Figure 7 Schematic diagram of the top component of the present invention Figure 1 ; Figure 8 Schematic diagram of the top component of the present invention Figure 2 .

[0020] In the diagram: 1. Pushing device; 101. Connecting plate; 102. Air inlet pipe; 103. Air supply device; 104. Detection device; 105. Air outlet pipe; 2. Central mechanism; 201. Outer frame; 202. Heating device; 203. Purge bottle; 21. Adjustment assembly; 211. Motor; 212. Housing; 213. Groove; 214. Baffle; 215. Push rod; 216. Rotating ring; 217. Connecting ring; 22 221. Fixing component; 222. Connecting column; 223. U-shaped plate; 224. Connecting head; 225. First slider; 226. Connecting rod; 227. Second slider; 228. Elastic component; 23. Fixing head; 23. Top component; 231. Cover plate; 232. Vent ring; 233. Vent plate; 234. Air outlet plate; 235. Protruding plate; 236. Air outlet; 237. Air inlet; 238. Liquid inlet. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] A purge-trap pretreatment method for detecting volatile organic compounds in soil includes the following steps: S1. Weigh a quantitative soil sample and place it in the purge bottle 203. Drive the top component 23 down by the pushing device 1 to close the purge bottle 203. Then add a quantitative blank reagent water through the injection needle. Stir to disperse the sample evenly and form a mud. S2. Start the heating device 202 to control the temperature of the purge bottle 203, and under constant temperature conditions, introduce inert gas to purge by bubbling, so that the volatile organic compounds in the mud can escape with the carrier gas. S3. The escaped gas enters the detection device 104 through the gas outlet pipe 105. In the detection device 104, the gas is dried and purged to remove moisture, then heated to desorb, and finally introduced into the gas chromatography system for detection.

[0025] In S1, the mass-to-volume ratio of soil sample to blank reagent water is 1:1 to 1:3, and the mixing time is 8 to 15 min, ensuring that the soil particles are completely dispersed in the slurry after mixing. In S2, the isothermal purging temperature is 40℃ to 60℃; the inert gas is pure helium or pure nitrogen, the purging gas flow rate is 30 to 50 mL / min, and the purging time is 8 to 12 min. In S3, the desorption temperature is 180℃ to 250℃, and the desorption time is 1 to 4 min. The gas chromatography system uses a weakly polar capillary column for separation, and the stationary phase of the column is a bonded cross-linked weakly polar polysiloxane.

[0026] Example 1: This example illustrates the specific operational process of a gradient verification experiment for the optimal water addition amount: Sample preparation: Five 5.0g air-dried and sieved soil samples were weighed and placed in 40mL purge bottles respectively. Isopropanol standard solution was added to each soil sample to make the theoretical spiking concentration of isopropanol in the soil reach 50.0μg / kg. The samples were allowed to stand for 24 hours to allow the target substance to be fully adsorbed and balanced with the soil matrix.

[0027] Table 1 shows the specific experimental groups for this gradient verification experiment.

[0028] Group design description: The water addition gradient covers the complete range from "no water" to "excess water"—0 mL, 1 mL, 5 mL, 10 mL, and 15 mL, which facilitates the systematic investigation of the influence of water addition on the recovery rate.

[0029] Purge and trap parameter settings: Referring to the HJ605-2011 standard method and the parameter range in this technical solution, the parameters of the purge and trap instrument are set as follows: Table 2 shows the specific parameter settings for the purge trap.

[0030] Gas chromatography-mass spectrometry analysis parameters: Referring to the HJ 605-2011 standard method, the GC-MS analysis parameters are set as follows: Table 3 shows the settings for GC-MS analysis parameters.

[0031] Measurement method: Seven parallel samples were set up in each group. After adding a magnetic stir bar to each purge bottle, the bottle was quickly capped and sealed. Purge and trapping and GC-MS analysis were performed sequentially according to the instrument parameters mentioned above. Then, the internal standard method was used for quantification. The internal standard was a compound with similar physicochemical properties to isopropanol and not present in the sample, such as n-propanol. After the determination of each sample, the chromatographic peak area of ​​isopropanol was recorded. The concentration was calculated according to the standard curve. Then, the recovery rate after adding blank reagent water in each group was calculated, i.e., the spiked recovery rate.

[0032] Experimental results: Table 4 shows the effect of different water addition amounts on the isopropanol purge-and-trap recovery rate in soil.

[0033] In the table above, the recovery rate is calculated according to the formula "Recovery rate (%) = (Measured concentration / Spiked concentration) × 100%"; RSD is the relative standard deviation, which is used to reflect the precision of 7 parallel determinations.

[0034] Based on the data from the five sets of comparative experiments above, a non-monotonic relationship exists between the amount of water added and the isopropanol recovery rate: when the water added increases from 0 mL to 10 mL, the recovery rate continuously rises from 64.8% to 97.4%, while the RSD decreases from 14.2% to 3.1%; however, when the water added continues to increase to 15 mL, the recovery rate drops to 82.3%, showing a pattern of first increasing and then decreasing. Combined with the data from this experiment, it can be concluded that an added water volume of 10 mL, i.e., a water-to-soil volume ratio of 1:2, is the optimal condition. At this point, the soil is completely transformed into a homogeneous mud system, the gully effect is completely eliminated, and the recovery rate is optimal. The highest recovery rate and optimal precision were achieved. This result proves that the 5mL to 15mL water addition range used in this technical solution is the optimal parameter range obtained through creative work. Below this range, an effective slurry cannot be formed to eliminate the channeling effect, while above this range, the recovery rate decreases due to the increased heat capacity of the system and the increased water vapor load. At the same time, this experiment also verified the effectiveness of the drying and purging step: performing a 2-minute drying and purging after purging and before desorption can effectively remove water vapor interference while ensuring zero loss of isopropanol, ensuring that the chromatographic analysis is not affected by the water peak.

[0035] Example 2: To address the water vapor interference caused by a high proportion of water addition, this example is used to verify the effect of drying and purging in step 3. Specifically, based on the experimental group in Example 1, the effect of turning the drying and purging function on and off is compared. The specific results are as follows: Without drying and purging: the water peak in the chromatogram was severely tailed and caused baseline interference to the isopropanol peak for up to 3.5 minutes, while the signal-to-noise ratio was only 45. After starting the drying purge and continuing for 2 minutes: the water peak area decreased by more than 90%, the isopropanol peak became sharp and symmetrical, and the signal-to-noise ratio increased to 120.

[0036] The results in summary demonstrate that the present invention, through a water removal strategy at the parameter setting level, can successfully solve the water vapor interference caused by the mud system without the need for additional chemical dewatering agents.

[0037] Example 3: To verify the applicability of the water addition range of the present invention to different types of VOCs, this example selects three representative VOCs with different water solubility for comparative experiments: Material preparation: Take air-dried and sieved sandy loam soil from a certain location, and after drying and testing, ensure that it does not contain the target substance; Spike treatment: Weigh 5.0g of soil samples into each of the three groups and add standard solutions of isopropanol, ethyl acetate and toluene to each group of soil samples to make the concentration of each target substance reach 50μg / kg. Let stand for 24 hours to equilibrate. Experimental groups: All experimental groups adopted the purge and trap method disclosed in this invention. The amount of blank reagent water added was set to 10 mL. The mixture was stirred for 11 min to form a homogeneous slurry. The purge temperature was 40℃, the purge time was 11 min, and the flow rate was 40 mL / min. Experimental results: Table 5 shows the recovery results of different water-soluble VOCs under the same environment.

[0038] Data shows that the present invention, using 10 mL of blank reagent water, can achieve a high recovery rate of over 95% for VOCs with different water solubility, with good precision. Among them, isopropanol, which has the highest water solubility, has the highest recovery rate. This is consistent with the principle in step one of the present invention, which utilizes the polar elution effect of water to displace the target substance from the surface of soil particles to the aqueous phase—the higher the water solubility of the target substance, the easier it is to be eluted from the soil surface into the aqueous phase by water, thus being more fully extracted during the purging process. This result verifies that the water addition range of the present invention has good applicability to various VOCs, without the need to adjust the water addition amount for different target substances.

[0039] Therefore, as can be seen from the above, the present invention uses isopropanol as a representative target compound for water addition optimization experiments because isopropanol is one of the most water-soluble compounds among VOCs, and its purging efficiency is most affected by the aqueous phase, making it the most difficult type of substance to extract in the purging and trapping method. According to the basic principle of purging and trapping, the purging efficiency of a target compound is negatively correlated with its solubility in water—the higher the solubility of a component, the lower its purging efficiency. Therefore, if a certain water addition condition can achieve an excellent recovery rate for isopropanol, which is the most difficult to purge, then that condition will inevitably achieve a comparable or higher recovery rate for other VOCs with lower water solubility.

[0040] This conclusion has been verified by existing technology: standard methods such as HJ 605-2011 can simultaneously measure dozens or even sixty-five different VOCs using uniform purging conditions, indicating that uniform conditions covering multiple VOCs is a recognized feasible technical solution in this field; based on uniform water addition, this invention further eliminates the channeling effect by constructing a mud system, thereby improving the purging efficiency of various VOCs.

[0041] Furthermore, those skilled in the art will understand that the determination of the water addition range of "5mL to 15mL" in this invention is based on the physical requirement of "sufficient to form a homogeneous mud system to eliminate the channeling effect," rather than the stoichiometric requirement for a specific target analyte. As long as the mud system is formed, the purging gas can pass through the sample system uniformly in the form of tiny bubbles, the channeling effect will be eliminated, and the purging efficiency of various VOCs can be guaranteed.

[0042] Example 4: See Figures 1-8 The present invention provides a technical solution: a purge-trap pretreatment device for detecting volatile organic compounds in soil. A connecting plate 101 is fixedly connected to the top of the pushing device 1, a top component 23 is fixedly connected to the inner wall of the connecting plate 101, a central mechanism 2 is fixedly connected to the outer wall of the pushing device 1, an air supply device 103 is fixedly connected to the rear side of the pushing device 1, a detection device 104 is fixedly connected to the rear side of the pushing device 1, an air inlet pipe 102 is fixedly connected to the air outlet of the air supply device 103, and an air outlet pipe 105 is fixedly connected to the air inlet of the detection device 104. The front ends of both the air inlet pipe 102 and the air outlet pipe 105 are fixedly connected to the top component 23. During operation, a quantitative soil sample is placed in a purge bottle 203, and blank reagent water is added at a mass-volume ratio of 1:1 to 1:3. The pushing device 1 drives the top component 23 to move down, so that the cover plate 231 covers the purge bottle 203 to form a closed system; then the adjusting component 21 drives the purge bottle 203 to rotate and stir, so that the soil and reagent water are fully mixed to form a homogeneous slurry; water, as a polar solvent, replaces the polar volatile organic compounds on the surface of soil particles to the aqueous phase based on the principle of "like dissolves like", thereby reducing mass transfer resistance.

[0043] The central mechanism 2 includes an outer frame 201, a heating device 202 is fixedly connected to the inner wall of the outer frame 201, and an adjustment component 21 is rotatably connected to the inner wall of the outer frame 201 via a bearing. A purge bottle 203 is placed on the top of the adjustment component 21.

[0044] The adjustment assembly 21 includes a motor 211, the bottom of which is fixedly connected to the outer frame 201. A housing 212 is fixedly connected to the output end of the motor 211. The outer wall of the housing 212 is rotatably connected to the outer frame 201 via bearings. A baffle 214 is fixedly connected to the top of the housing 212, and a slot 213 is provided on the top of the housing 212. A push rod 215 is fixedly connected to the inner wall of the outer frame 201, and a connecting ring 217 is fixedly connected to the top of the push rod 215. The top of the connecting ring 217 is connected to a bearing. A rotating ring 216 is rotatably connected, and a fixing component 22 is fixedly connected to the inner wall of the rotating ring 216. During the purging process, the motor 211 drives the outer shell 212 and the purging bottle 203 to rotate continuously. The fixing component 22, together with the baffle 214, clamps and limits the purging bottle 203 to ensure stable rotation. The air outlet plate 234 and the protruding plate 235 act as obstacles to shear and turbulence the rotating mud, enhance the degree of turbulence, promote the contact between soil particles and the water phase, and accelerate the mass transfer of the target material from the solid phase to the water phase.

[0045] The fixing assembly 22 includes a connecting post 221, the outer wall of which is fixedly connected to a rotating ring 216. A U-shaped plate 222 is fixedly connected to the top of the connecting post 221. A connector 223 is fixedly connected to the inner wall of the U-shaped plate 222. A first slider 224 is fixedly connected to the outer wall of the connector 223. The inner wall of the first slider 224 is movably connected to the outer shell 212. A connecting rod 225 is rotatably connected to the inner wall of the connector 223 via a bearing. A second slider 226 is rotatably connected to the end of the connecting rod 225 away from the connector 223 via a bearing. The outer wall of the second slider 226 is connected to the groove 216. 3. Movable connection: The top of the second slider 226 is fixedly connected to the fixing head 228, and the end of the second slider 226 away from the connecting head 223 is fixedly connected to the elastic component 227. The outer wall of the elastic component 227 is fixedly connected to the outer shell 212. When the purge bottle 203 is placed on the top of the outer shell 212, the push rod 215 extends upward, pushing the connecting ring 217 and the rotating ring 216 to rise. The rotating ring 216 drives the first slider 224 to slide upward, and pushes the second slider 226 inward along the slot 213 through the connecting rod 225, so that the fixing head 228 moves closer to the bottle mouth of the purge bottle 203.

[0046] The top assembly 23 includes a cover plate 231, which is fitted onto the top of the purge bottle 203. An air outlet 236 is fixedly connected to the top of the cover plate 231, and the top of the air outlet 236 is fixedly connected to the air outlet pipe 105. An air inlet 237 is fixedly connected to the top of the cover plate 231, and the top of the air inlet 237 is fixedly connected to the air inlet pipe 102. A venting ring 232 is fixedly connected to the bottom of the cover plate 231, and a venting plate 233 is fixedly connected to the bottom of the venting ring 232. An air outlet plate 234 is fixedly connected to the bottom of the venting plate 233, and a protruding plate 235 is fixedly connected to the outer wall of the air outlet plate 234. A liquid inlet 238 is opened on the top of the cover plate 231. The heating device 202 keeps the temperature of the purge bottle 203 constant at 40℃~60℃. The high-purity inert gas supplied by the gas supply device 103 enters the top component 23 through the air inlet pipe 102. After being diverted sequentially through the air inlet 237, the air ring 232, and the air plate 233, it is uniformly introduced into the mud at multiple angles in the form of microbubbles through the arc-shaped porous air outlet plate 234, greatly increasing the gas-liquid contact area. After the bubbles carry the volatile organic compounds escaping from the aqueous phase to the liquid surface, they enter the detection device 104 through the air outlet plate 234, the air outlet 236, and the air outlet pipe 105.

[0047] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0048] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pretreatment method for purge-trap detection of volatile organic compounds in soil, characterized in that: Includes the following steps: S1. Weigh a quantitative soil sample and place it in a purge bottle (203). Drive the top component (23) down by the pushing device (1) to close the purge bottle (203). Then add a quantitative blank reagent water through the injection needle. Stir to disperse the sample evenly and form a mud. S2. Start the heating device (202) to control the temperature of the purge bottle (203) and purge with inert gas under constant temperature conditions, so that the volatile organic compounds in the mud can escape with the carrier gas. S3. The escaping gas enters the detection device (104) through the gas outlet pipe (105). In the detection device (104), the moisture is removed by drying and purging, followed by heating and desorption, and finally introduced into the gas chromatography system for detection.

2. The pretreatment method for purge-trap detection of volatile organic compounds in soil according to claim 1, characterized in that: In S1, the mass-to-volume ratio of soil sample to blank reagent water is 1:1 to 1:3, the mixing time is 8 to 15 minutes, and the soil particles are completely dispersed in the mud after mixing.

3. The pretreatment method for purge-trap detection of volatile organic compounds in soil according to claim 1, characterized in that: In S2, the temperature for constant temperature purging is 40℃~60℃; the inert gas is pure helium or pure nitrogen, the purging gas flow rate is 30~50 mL / min, and the purging time is 8~12 min.

4. The pretreatment method for purge-trap detection of volatile organic compounds in soil according to claim 1, characterized in that: In S3, the desorption temperature is 180℃~250℃ and the desorption time is 1~4 min; the gas chromatography system uses a weakly polar capillary column for separation, and the stationary phase of the column is a bonded cross-linked weakly polar polysiloxane.

5. A purge-and-trap pretreatment device for detecting volatile organic compounds in soil, characterized in that: A connecting plate (101) is fixedly connected to the top of the pushing device (1). A top component (23) is fixedly connected to the inner wall of the connecting plate (101). A central mechanism (2) is fixedly connected to the outer wall of the pushing device (1). An air supply device (103) is fixedly connected to the rear side of the pushing device (1). A detection device (104) is fixedly connected to the rear side of the pushing device (1). An air inlet pipe (102) is fixedly connected to the air outlet end of the air supply device (103). An air outlet pipe (105) is fixedly connected to the air inlet end of the detection device (104). The front end of the air inlet pipe (102) and the front end of the air outlet pipe (105) are both fixedly connected to the top component (23).

6. The purge-and-trap pretreatment device for detecting volatile organic compounds in soil according to claim 5, characterized in that: The central mechanism (2) includes an outer frame (201), a heating device (202) is fixedly connected to the inner wall of the outer frame (201), and an adjustment component (21) is rotatably connected to the inner wall of the outer frame (201) via a bearing. A purge bottle (203) is placed on the top of the adjustment component (21).

7. The purge-and-trap pretreatment device for detecting volatile organic compounds in soil according to claim 6, characterized in that: The adjustment component (21) includes a motor (211), the bottom of which is fixedly connected to the outer frame (201). The output end of the motor (211) is fixedly connected to a housing (212). The outer wall of the housing (212) is rotatably connected to the outer frame (201) via a bearing. A baffle (214) is fixedly connected to the top of the housing (212). A slot (213) is provided on the top of the housing (212). A push rod (215) is fixedly connected to the inner wall of the outer frame (201). A connecting ring (217) is fixedly connected to the top of the push rod (215). A rotating ring (216) is rotatably connected to the top of the connecting ring (217) via a bearing. A fixing component (22) is fixedly connected to the inner wall of the rotating ring (216).

8. The purge-and-trap pretreatment device for detecting volatile organic compounds in soil according to claim 7, characterized in that: The fixing component (22) includes a connecting post (221), the outer wall of which is fixedly connected to a rotating ring (216). A U-shaped plate (222) is fixedly connected to the top of the connecting post (221), and a connector (223) is fixedly connected to the inner wall of the U-shaped plate (222). A first slider (224) is fixedly connected to the outer wall of the connector (223), and the inner wall of the first slider (224) is movably connected to the outer shell (212). The inner wall of the connector (223) is rotated by a bearing. A connecting rod (225) is movably connected. The end of the connecting rod (225) away from the connecting head (223) is rotatably connected to a second slider (226) via a bearing. The outer wall of the second slider (226) is movably connected to the slot (213). A fixing head (228) is fixedly connected to the top of the second slider (226). An elastic component (227) is fixedly connected to the end of the second slider (226) away from the connecting head (223). The outer wall of the elastic component (227) is fixedly connected to the outer shell (212).

9. A purge-and-trap pretreatment device for detecting volatile organic compounds in soil according to claim 8, characterized in that: The top assembly (23) includes a cover plate (231), which is fitted onto the top of the purge bottle (203). An air outlet (236) is fixedly connected to the top of the cover plate (231), and the top of the air outlet (236) is fixedly connected to an air outlet pipe (105). An air inlet (237) is fixedly connected to the top of the cover plate (231), and the top of the air inlet (237) is fixedly connected to an air inlet pipe (102). A venting ring (232) is fixedly connected to the bottom of the cover plate (231), and a venting plate (233) is fixedly connected to the bottom of the venting ring (232). An air outlet plate (234) is fixedly connected to the bottom of the venting plate (233), and a protruding plate (235) is fixedly connected to the outer wall of the air outlet plate (234). A liquid inlet (238) is opened on the top of the cover plate (231).

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