An efficient extraction method for soil samples to be measured for semi-volatile organic compounds

Abstract

The present application relates to an efficient extraction method for soil semi-volatile organic matter samples to be measured. The method includes the following steps: 1) Sample preparation: Take a soil sample and grind it to a particle size of 60 - 300 mesh to obtain a sample; 2) Ultrasonic extraction: Weigh the sample, surrogate, and auxiliary agent, add the n-hexane-acetone solvent, and then perform ultrasonic extraction at a temperature of 25°C ≤ temperature < 30°C for 15 minutes under a pressure of 0.05 Mpa in a pulsed mode. This ultrasonic extraction process is repeated three times to obtain sample A; 3) Filtration and dehydration: Centrifuge sample A, filter the obtained supernatant, and dehydrate the filtered filtrate to obtain sample B; 4) Concentration and volume fixation: Concentrate sample B to 1 - 2 mL to obtain a concentrated solution; then add the n-hexane-acetone mixed solvent and mix it evenly with the concentrated solution to obtain an extract, and then concentrate the extract to less than 1 mL, fix the volume, obtain the sample to be measured, and store it refrigerated for measurement.

Description

Technical Field

[0001] This application relates to the technical field of the extraction of semi-volatile organic compounds in soil, and particularly relates to an efficient extraction method for soil semi-volatile organic compound samples to be tested. Background Art

[0002] The extraction and testing of semi-volatile organic compounds (SVOCs) are key links in environmental monitoring, risk assessment, and pollution control. Their importance lies not only in the quantitative analysis of environmental pollution status but also in providing reliable data support for scientific decision-making. With the development of modern environmental management towards refinement, the research and monitoring of SVOCs play an increasingly important role in the whole-life cycle management of pollutants. Especially driven by advanced analytical techniques such as non-target screening and isotope tracing, efficient extraction methods have become the core requirement for improving detection efficiency and accuracy, directly affecting the overall level of environmental monitoring.

[0003] Currently, for the extraction of semi-volatile organic compounds in soil, common methods include Soxhlet extraction, pressurized fluid extraction (PFE), and ultrasonic extraction. The Soxhlet extraction method achieves continuous extraction through the cyclic reflux of the solvent. Usually, a dichloromethane-acetone mixed solvent is used, and the operation is carried out in a Soxhlet thimble for 16 - 18 hours, and the material transfer is completed by siphon action; the pressurized fluid extraction technology realizes rapid extraction through static extraction under high temperature and pressure conditions combined with nitrogen purging; the ultrasonic extraction method is based on the cavitation effect of sound waves, and the release of the target substance from the soil matrix is accelerated through the oscillation effect. In addition, other auxiliary means such as freezing treatment and dehydration treatment are applied in the sample pretreatment stage to improve the extraction efficiency or reduce impurity interference.

[0004] However, the existing technical means generally face multiple challenges in terms of efficiency, economy, and accuracy. For example, although the Soxhlet extraction method has a wide application range, it is time-consuming and has a large solvent consumption, making it difficult to meet the requirements of high-throughput analysis; although the pressurized fluid extraction can significantly shorten the time, the equipment cost is high, and the high temperature conditions may cause the degradation of heat-sensitive substances; and the current ultrasonic extraction method requires grinding the soil sample to several micrometers or even nanometers, so it is easy to form colloids or dispersions during the extraction process, thereby reducing the extraction efficiency and content accuracy, especially performing poorly in complex soil matrices. Therefore, how to improve efficiency and reduce costs while ensuring extraction accuracy has become a key problem to be solved urgently. Summary of the Invention

[0005] In order to improve the extraction efficiency, reduce costs, and ensure its accuracy at the same time, this application provides an efficient extraction method for soil semi-volatile organic compound samples to be tested.

[0006] An efficient extraction method for soil semi-volatile organic compound samples to be tested includes the following steps:

[0007] 1) Sample preparation: Take soil samples and grind them to a particle size of 60 - 300 mesh to obtain samples;

[0008] 2) Ultrasonic extraction: Weigh the sample, surrogate, and auxiliary agent in a weight ratio of 1:(0.8 - 1):(0.05 - 0.1), then add n - hexane - acetone solvent. The volume ratio of n - hexane - acetone solvent to the weight of the sample is (2 - 3):1, and then perform ultrasonic extraction at a temperature of 25℃ ≤ temperature < 30℃ for 15 min under a pressure of 0.05 Mpa in pulse mode. This ultrasonic extraction process is repeated three times, with an interval of 0.5 - 2 min each time to obtain sample A. Among them, the auxiliary agent is anhydrous sodium sulfate or sodium chloride;

[0009] 3) Filtration and dehydration: Centrifuge sample A, then filter the obtained supernatant, and dehydrate the filtered filtrate to obtain sample B;

[0010] 4) Concentration and volume fixation: Concentrate sample B to 1 - 2 mL to obtain a concentrated solution; then add n - hexane - acetone mixed solvent and mix it evenly with the concentrated solution. The weight ratio of n - hexane - acetone mixed solvent to the concentrated solution is (7.5 - 15):1 to obtain an extract, and then concentrate the extract to less than 1 mL and fix the volume to 1 mL with n - hexane - acetone to obtain a sample to be measured, and then transfer it to a brown sample bottle for refrigerated measurement.

[0011] By adopting the above technical solutions, efficient extraction of semi - volatile organic compounds in soil can be achieved. The specific effects are as follows: First, by grinding the soil sample to a particle size of 60 - 300 mesh, the specific surface area of soil particles is significantly increased, thereby improving the subsequent extraction efficiency. At the same time, it can avoid the generation of colloids or dispersoids during the ultrasonic extraction process, thus affecting the extraction accuracy and efficiency. Second, during the ultrasonic extraction process, n - hexane - acetone solvent is used, combined with temperature control of 25℃ to less than 30℃, a pressure of 0.05 Mpa, and pulse mode, effectively utilizing the cavitation effect to destroy the soil particle structure, accelerating the dissolution and release of target substances, while avoiding the degradation of heat - sensitive substances and the loss of solvent volatilization. The auxiliary agent is anhydrous sodium sulfate or sodium chloride, which can promote the release of target substances from soil particles through salting - out effect, reduce emulsification phenomenon, and reduce the generation of its colloids. This process is repeated three times to further improve the thoroughness of extraction. Then, the centrifugation treatment and two - stage filtration design not only effectively separate particulate impurities but also reduce the adsorption loss of the filter membrane, ensuring the purity of the extract. Finally, the concentration and volume fixation steps precisely control the solution volume, avoid the loss of semi - volatile organic compounds, improve the recovery rate and detection accuracy, and finally obtain a stable and reliable sample to be measured.

[0012] Regarding the concentration to less than 1 mL in the steps, since it is difficult to accurately concentrate to 1 mL each time, when the concentration reaches less than 1 mL, then make up the volume, so as to ensure that the amount of the final sample is unified.

[0013] Preferably, the sample preparation in step 1) further includes a freezing treatment. The specific process of the sample preparation in step 1) is as follows: Take the soil sample for vacuum cooling, the freezing temperature is -40°C to -30°C, the freezing time is 18 - 20 h, and then grind it to a particle size of 60 - 300 mesh to obtain the sample.

[0014] By adopting the above technical solution, the soil sample is subjected to vacuum cooling treatment, the freezing temperature is controlled at -40°C to -30°C, the freezing time is set to 18 - 20 hours, and then the sample is ground to a particle size less than 0.1 mm. This method can effectively fix the state of semi-volatile organic compounds in the soil, reduce the loss of target substances during sample pretreatment, and improve the accuracy and recovery rate of subsequent extraction. Specifically, the freezing treatment helps to inhibit the activity of microorganisms, prevent the degradation of target substances, and at the same time reduce the agglomeration of particles during the sample grinding process, improve the sample homogeneity, thus providing a guarantee for efficient extraction.

[0015] Preferably, the sample preparation in step 1) further includes a dehydration treatment. The specific process of the sample preparation in step 1) is as follows: Take the soil sample and mix it with anhydrous sodium sulfate in a weight ratio of 1:(1 - 1.4) for dehydration, then grind it to a particle size of 60 - 300 mesh and make it in a flowing sand state.

[0016] By adopting the above technical solution, it can effectively remove the moisture in the soil sample and avoid the interference of moisture on the dissolution and separation of semi-volatile organic compounds during subsequent extraction. Specifically, by mixing the soil sample with anhydrous sodium sulfate in a specific ratio for dehydration treatment, the drying degree of the sample can be significantly improved, and at the same time, the particle agglomeration phenomenon is reduced, making the sample easier to grind to the required particle size, thus improving the efficiency and accuracy of subsequent ultrasonic extraction. In addition, the sample after dehydration treatment is in a flowing sand state, which is beneficial to increasing the contact area between the sample and the solvent and further enhancing the extraction effect.

[0017] Preferably, the volume ratio of n-hexane to acetone in the n-hexane - acetone solvent is 2 - 3:1.

[0018] By adopting the above technical solution, the volume ratio of n-hexane to acetone is optimized to 2 - 3:1, which can further enhance the dissolution ability of the solvent for semi-volatile organic compounds, ensure that the target substances are more efficiently released from the soil and dissolved in the solvent. At the same time, this ratio reduces the instability and volatilization loss of the solvent system while ensuring the extraction efficiency, thus improving the stability and recovery rate of the extraction process.

[0019] Preferably, the centrifugation rate for the centrifugation treatment is 5000 - 8000 rpm, and the time is 10 - 20 min.

[0020] By adopting the above technical solution, the parameters of the centrifugation treatment are optimized to a centrifugation rate of 5000 - 8000 rpm and a time of 10 - 20 min, which can effectively avoid the adsorption loss of the filter membrane, and is especially suitable for viscous soil samples with a high particulate content. This optimization significantly improves the accuracy of the product and ensures the accuracy and reliability of the extraction of semi-volatile organic compounds in the subsequent analysis process.

[0021] Preferably, the specific filtration process in the filtration and dehydration in step 3) is as follows: First, filter with a glass fiber filter membrane with a pore size of 1.0 - 2.0 µm, and then filter the obtained filtrate with a glass fiber filter membrane with a pore size of 0.4 - 0.5 µm.

[0022] By adopting the above technical solution, first using a glass fiber filter membrane with a pore size of 1.0 - 2.0 µm for rough filtration can effectively remove larger particle impurities in the filtrate and reduce the risk of filter membrane blockage in the subsequent fine filtration process; then using a glass fiber filter membrane with a pore size of 0.4 - 0.5 µm for fine filtration can further improve the purity of the filtrate and ensure the extraction effect and accuracy of the target semi-volatile organic compounds. In addition, the glass fiber filter membrane is soaked in a n-hexane - acetone solvent and activated by nitrogen blowing before use, which can significantly reduce the adsorption loss of the filter membrane to the target compounds, and is especially suitable for the efficient extraction of non-polar compounds such as polycyclic aromatic hydrocarbons.

[0023] Preferably, the dehydrating agent used in the dehydration process in the filtration and dehydration in step 3) is obtained by mixing anhydrous sodium sulfate and silica gel in a weight ratio of (4 - 5):1.

[0024] By adopting the above technical solution, the dehydrating agent formed by mixing anhydrous sodium sulfate and silica gel in a weight ratio of (4 - 5):1 can effectively remove the water in the filtrate, improve the dehydration efficiency, and at the same time reduce the loss of semi-volatile organic compounds during the dehydration process, thereby improving the accuracy and recovery rate of the extraction.

[0025] Preferably, the specific steps of the dehydration process in the filtration and dehydration in step 3) are as follows: Uniformly fill the dehydrating agent into a 50 mL syringe until the scale reaches 5 mL.

[0026] By adopting the above technical solution, uniformly filling the dehydrating agent into a 50 mL syringe until the scale reaches 5 mL can form a stable dehydration layer structure, ensuring the uniformity and efficiency of the dehydration process. This step, combined with the dehydrating agent obtained by mixing anhydrous sodium sulfate and silica gel, further improves the dehydration effect, reduces the water residue in the sample, and thus improves the accuracy of the extraction of semi-volatile organic compounds.

[0027] Preferably, the n-hexane and acetone in the n-hexane-acetone mixed solvent are composed in a volume ratio of 1:1 - 1.2.

[0028] By adopting the above technical solution, the n-hexane and acetone are composed in a volume ratio of 1:1 - 1.2, which can further optimize the solvent ratio, enhance the dissolution ability of semi-volatile organic compounds in the soil, thereby improving the extraction efficiency and recovery rate, and at the same time ensuring the stability and accuracy of the extraction process.

[0029] Preferably, in the concentration and volume fixation in step 4), the refrigeration temperature is -4 - 0°C, and the refrigeration time is less than 2 days.

[0030] By adopting the above technical solution, the sample to be measured after concentration and volume fixation is refrigerated in a low-temperature environment of -4 to 0°C, effectively inhibiting the volatilization and degradation of semi-volatile organic compounds, and ensuring their chemical stability. At the same time, the refrigeration time is limited to less than 2 days, further reducing the loss of the target substance caused by too long time, and improving the accuracy and reliability of the extraction method.

[0031] In summary, the present application includes at least one of the following beneficial technical effects:

[0032] 1. By optimizing the ultrasonic extraction parameters (such as temperature, pressure, pulse mode and repetition times), the extraction efficiency of semi-volatile organic compounds is effectively improved, and at the same time, the degradation of heat-sensitive substances is avoided, significantly enhancing the recovery rate of the target substance;

[0033] 2. Through centrifugation, multi-stage filtration and efficient dehydration treatment, the interference of impurities is effectively removed, ensuring the accuracy of the extraction process, especially suitable for complex soil matrices with high particulate matter content;

[0034] 3. The combination of concentration and volume fixation steps and low-temperature refrigeration reduces the loss of semi-volatile organic compounds, ensuring the stability of the extracted sample and the accuracy of subsequent analysis. Specific Embodiments

[0035] The technical solutions in the embodiments of the present invention are clearly and completely described below. The described embodiments are only possible technical implementations of the present invention, not all possible implementations. Those skilled in the art can completely combine the embodiments of the present invention to obtain other embodiments without creative labor, and these embodiments are also within the protection scope of the present invention.

[0036] The inventors of the present application have found that the extraction and testing of semi-volatile organic compounds (SVOCs) are key steps in environmental monitoring, risk assessment, and pollution control. Their importance lies not only in the quantitative analysis of environmental pollution conditions but also in providing reliable data support for scientific decision-making. However, existing methods have problems such as low efficiency, high cost, and unstable recovery rates. Therefore, the present application mainly adopts the following technical solutions, including sample preparation, ultrasonic extraction, filtration and dehydration, and concentration and volume fixation, etc., achieving the effects of improving extraction efficiency, reducing costs, and ensuring accuracy.

[0037] The high-efficiency extraction method for soil semi-volatile organic compound samples to be measured provided by the embodiments of the present application includes steps such as sample preparation, ultrasonic extraction, filtration and dehydration, and concentration and volume fixation. Among them, sample preparation and ultrasonic extraction cooperate with each other to improve extraction efficiency, and filtration and dehydration and concentration and volume fixation cooperate with each other to improve accuracy, achieving the effects of improving efficiency and reducing costs while ensuring extraction accuracy.

[0038] Example 1

[0039] A high-efficiency extraction method for soil semi-volatile organic compound samples to be measured includes the following steps:

[0040] 1) Sample preparation: Take a soil sample and grind it to a particle size of 200 mesh to obtain a sample; the specific process of this sample preparation is as follows: Sampling refers to collecting a representative soil sample from the target area to ensure that the sample can reflect the soil pollution status of the area; or it is a soil with known semi-volatile organic compounds. For example, a certain amount of semi-volatile organic compounds is added to soil without semi-volatile organic compounds, and then the extraction is carried out using the preparation method of the present application, and then the recovery rate is evaluated. This embodiment preferably adopts this method, and the humidity of the soil sample is 30%; during the grinding process, a commonly used laboratory ball mill or grinder is used to grind the soil sample to a particle size of 200 mesh, and the rotation speed of the grinder is controlled at 2000 - 3000 rpm, and the time is 5 - 10 min to ensure that the soil particles reach sufficient fineness. For example, replaceable grinding equipment includes a planetary ball mill or a vibration mill, and their rotation speed and time need to be adjusted appropriately according to the equipment performance.

[0041] Freezing treatment is also required: Specifically, place the soil sample in a vacuum freeze dryer, control the freezing temperature at -40°C to -30°C, and the freezing time is 18 - 20 h. In this embodiment, it is preferably -40°C and 20 h; to reduce the influence of moisture on the subsequent extraction process. Or an dehydration treatment method is adopted to dehydrate the soil with a relatively high moisture content. This dehydration treatment is carried out by mixing the soil sample with anhydrous sodium sulfate at a weight ratio of 1:(1 - 1.4), fully stirring and then standing for 30 min, and then grinding it to a flowing sand state (200 mesh) to remove excess moisture. In this embodiment, the method of first freeze-drying and then dehydration is adopted.

[0042] 2) Ultrasonic extraction: The sample, substitute, and auxiliary agent can be weighed and mixed at a weight ratio of 1:(0.8 - 1):(0.05 - 0.1). In this embodiment, it is preferably to weigh and mix the sample, substitute (4,4'-terphenyl-d14), and auxiliary agent at a weight ratio of 1:1:0.1. Then, n-hexane-acetone solvent is added. The volume ratio of the n-hexane-acetone solvent to the weight of the sample can be 2:1 or 3:1. In this embodiment, it is preferably 3:1. Then, it is placed in an ultrasonic device for ultrasonic extraction. The temperature is from 25°C to less than 30°C. In this embodiment, the temperature is controlled at a constant 25°C, and the temperature increase above 30°C during ultrasonic extraction is avoided. The time of ultrasonic treatment is 15 min, the pressure is 0.05 Mpa, and the pulse mode (working for 2 s / stopping for 1 s) is adopted. The ultrasonic instrument is a constant-temperature probe type instrument, and the frequency can be 40 kHz, 50 kHz, and 60 kHz. In this embodiment, it is preferably 50 kHz to enhance the cavitation effect and avoid local overheating. This ultrasonic extraction process is repeated three times, with an interval of 0.5 - 2 min each time, preferably 1 min, to obtain sample A. Among them, the auxiliary agent is anhydrous sodium sulfate or sodium chloride. In this embodiment, it is sodium chloride, and its sodium chloride promotes the release of the target substance from soil particles through salting-out effect and reduces the emulsification phenomenon.

[0043] 3) Filtration and dehydration: Sample A is centrifuged, and the obtained supernatant is filtered again. The filtered filtrate is dehydrated to obtain sample B. Specifically, filtration and dehydration include centrifugation, membrane filtration, and application of dehydrating agent. The centrifugation is carried out using a high-speed centrifuge. The rotation speed can be 5000 rpm, 6000 rpm, 7000 rpm, or 8000 rpm, preferably 8000 rpm. The time can be 10 min, 15 min, or 20 min to separate the solid and liquid phases. In this embodiment, it is preferably 20 min. The membrane filtration is carried out in two steps. First, it is roughly filtered with a glass fiber filter membrane with a pore size of 1.0 - 2.0 µm, preferably a pore size of 1.0 µm. Then, it is finely filtered with a glass fiber filter membrane of 0.4 - 0.5 µm. The preferred particle size is to reduce the risk of blockage. The glass fiber filter membrane is soaked in n-hexane-acetone solvent for 30 min and activated by nitrogen blowing before use to reduce adsorption loss. The dehydrating agent is composed of anhydrous sodium sulfate and silica gel at a weight ratio of 4:1 or 5:1. In this embodiment, it is a mixture of anhydrous sodium sulfate and silica gel at a ratio of 5:1. The dehydrating agent is evenly filled in a 50 mL syringe to the 5 mL mark to form a dehydration layer. A hydrophobic PTFE 0.45 µm needle filter is installed at the syringe mouth to ensure complete dehydration of the filtrate.

[0044] 1. Concentration and volume fixation: Concentrate sample B to 1 - 2 mL to obtain a concentrated solution; then add a mixed solvent of n - hexane - acetone and mix it evenly with the concentrated solution. The weight ratio of the n - hexane - acetone mixed solvent to the concentrated solution is (7.5 - 15):1 to obtain an extract. Then concentrate the extract to less than 1 mL and fix the volume to 1 mL with n - hexane - acetone to obtain a test sample containing 4,4'-biphenyld14, and then transfer it to a brown sample bottle for refrigeration and waiting for testing.

[0045] When the surrogates are replaced with nitrobenzene - d5 and phenol - d5 respectively, then repeat the processes of steps 1) - 4) respectively to obtain a test sample containing nitrobenzene - d5 and a test sample containing phenol - d5 respectively, and then carry out refrigeration.

[0046] Specifically: Concentration and volume fixation include concentration, mixing and dilution, re - concentration and volume fixation. In the concentration process, a rotary evaporator is used to concentrate sample B to 1 - 2 mL under the condition of a 40 °C water bath. In this example, it is concentrated to 1 mL to obtain a concentrated solution. When mixing and diluting, the weight ratio of the n - hexane - acetone mixed solvent to the concentrated solution can be 7.5:1 or 15:1. In this example, the ratio of 1:15 is adopted; mix them evenly. When re - concentrating, concentrate the extract to less than 1 mL, and finally fix the volume to 1 mL with n - hexane - acetone, transfer it to a brown sample bottle, and refrigerate it at - 4 - 0 °C for no more than 2 days. In this example, the refrigeration temperature is - 4 °C and the time is 2 h.

[0047] In addition, the semi - volatile organic compounds contained in the test sample include 5 μg / mL of compound BaP, 5 μg / mL of 2 - Chlorophenol, 5 μg / mL of NITR (nitrobenzene), and 5 μg / mL of BkF (benzo(k)fluoranthene).

[0048] Comparative Example 1

[0049] The difference between Comparative Example 1 and Example 1 is that: the ultrasonic extraction process is replaced with a Soxhlet extraction method (such as the Soxhlet extraction method in GB HJ 834 - 2017). The sample is loaded into a Soxhlet extraction thimble and reflux - extracted for 18 hours with a mixed solvent of dichloromethane - acetone (volume ratio 1:1), and the reflux speed is controlled at 4 times per hour. Utilizing the principle of solvent reflux and siphon, continuously extract the target compound from the solid sample to obtain sample A.

[0050] Comparative Example 2

[0051] The difference between Comparative Example 2 and Example 1 is that: the ultrasonic extraction process is replaced with a pressurized fluid extraction method (such as the pressurized fluid extraction method in GB HJ 834 - 2017). The pressurized fluid extraction method sets the heating temperature at 100 °C, the static extraction time at 5 minutes, and the nitrogen purge time at 1 minute, and repeats the extraction 3 times to obtain sample A.

[0052] Comparative Example 3

[0053] The difference between Comparative Example 3 and Example 1 is that in step 1), it is ground to a particle size of 1000 mesh.

[0054] (1) Perform separate recovery rate tests on the refrigerated test samples containing nitrobenzene-d5, the test samples containing phenol-d5, and the test samples containing 4,4'-terphenyl-d14 obtained in Example 1 and Comparative Examples 1-3:

[0055] Use a gas chromatography-mass spectrometry (GC-MS) instrument to measure 4,4'-terphenyl-d14, nitrobenzene-d5, phenol-d5, BaP, 2-chlorophenol, NITR, and BkF in the test samples, and then compare with the amounts used before recovery to calculate their test recovery rates; the specific experimental data are shown in Table 1;

[0056] Table 1 Experimental data of Example 1 and Comparative Examples 1-3

[0057]

[0058] Combining Example 1 and Comparative Examples 1-3 and referring to Table 1, it can be seen that the recovery rates of Comparative Examples 1-3 are all lower than that of Example 1, indicating that using the process and parameters of the present application can effectively improve efficiency, reduce the loss of semi-volatile organic compounds, and improve the recovery rate and recovery accuracy.

[0059] 1. Replace the soil samples used in Example 1 and Comparative Examples 1-3 with soil samples extracted from Xiaoshan District, Hangzhou. Then refer to the method in (1) to detect the recovery rate and content.

[0060] The specific experimental data are shown in Table 2;

[0061] Table 2 Experimental data of Example 1 and Comparative Examples 1-3

[0062]

[0063] Combining Example 1 and Comparative Examples 1-3 and referring to Table 1, it can be seen that the reduction range of the recovery rate of the substitutes in Comparative Examples 1-3 is significantly lower than that of Example 1, and the amounts of BaP, 2-chlorophenol, NITR, and BkF detected in Example 1 are also higher, indicating that the process of the present application can detect more semi-volatile substances and the test results are more accurate.

[0064] This specific embodiment is only an explanation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An efficient extraction method for soil semi-volatile organic matter samples to be measured, characterized in that, It includes the following steps: 1) Sample preparation: Take a soil sample and conduct vacuum cooling. The freezing temperature is -40°C to -30°C, and the freezing time is 18 - 20 h. Then grind it to a particle size of 200 - 300 mesh to obtain the sample; 2) Ultrasonic extraction: Weigh the sample, surrogate, and auxiliary agent in a weight ratio of 1:(0.8 - 1):(0.05 - 0.1) and mix them. Then add a n - hexane - acetone solvent. The volume ratio of the n - hexane - acetone solvent to the weight of the sample is (2 - 3):

1. Then conduct ultrasonic extraction. The temperature is 25°C ≤ temperature < 30°C, the time is 15 min, and the pressure is 0.05 Mpa. The pulse mode is adopted. This ultrasonic extraction process is repeated three times, with an interval of 0.5 - 2 min each time to obtain sample A. Among them, the auxiliary agent is sodium chloride; 3) Filtration and dehydration: Centrifuge sample A at a centrifuge speed of 5000 - 8000 rpm for 10 - 20 min. Filter the obtained supernatant, and dehydrate the filtered filtrate to obtain sample B; 4) Concentration and volume fixation: Concentrate sample B to 1 - 2 mL to obtain a concentrated solution; then add a n - hexane - acetone mixed solvent and mix it evenly with the concentrated solution. The weight ratio of the n - hexane - acetone mixed solvent to the concentrated solution is (7.5 - 15):1 to obtain an extract. Then concentrate the extract to less than 1 mL and fix the volume to 1 mL with n - hexane - acetone to obtain the sample to be measured. Then transfer it to a brown sample bottle for refrigeration and waiting for measurement; The volume ratio of n - hexane to acetone in the n - hexane - acetone solvent is 2 - 3:1; In the filtration process of step 3) filtration and dehydration, the specific process is as follows: First, filter with a glass fiber filter membrane with a pore size of 1.0 - 2.0 µm, and then filter the obtained filtrate with a glass fiber filter membrane of 0.4 - 0.5 µm; The dehydrating agent used in the dehydration process of step 3) filtration and dehydration is obtained by mixing anhydrous sodium sulfate and silica gel in a weight ratio of (4 - 5):1; The specific steps of the dehydration process in step 3) filtration and dehydration are as follows: Uniformly fill the dehydrating agent into a 50 mL syringe until the scale reaches 5 mL to form a dehydration layer; and install a hydrophobic PTFE 0.45 µm needle - type filter at the syringe mouth. When dehydrating, the filtered filtrate passes through the needle - type filter for filtration to separate the sodium sulfate solid and recycle it. The obtained filtrate is sample B; In step 4) concentration and volume fixation, the refrigeration temperature is -4 - 0°C, and the refrigeration time is less than 2 days.

2. The high-efficiency extraction method for the soil semi-volatile organic matter sample to be measured according to claim 1, wherein: In step 1) sample preparation, dehydration treatment is also included. The specific process of step 1) sample preparation is: Take a soil sample and mix it with anhydrous sodium sulfate in a weight ratio of 1:(1 - 1.4) for dehydration, then grind it to a particle size of 200 - 300 mesh and make it in a flowing sand state.

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