Analysis method for semi-volatile organic pollutants in four occurrence forms in site soil

Abstract

The invention discloses a method for analyzing semi-volatile organic pollutants in four occurrence forms in site soil, which comprises the following steps of: (1) extracting water-soluble semi-volatile organic pollutants: mixing polluted soil with anhydrous sodium sulfate, and extracting water-soluble components of the semi-volatile organic pollutants in the soil by adopting a CO2 supercritical fluid extraction method, collecting an extract for detection; (2) extraction of acid-soluble semi-volatile organic pollutants; (3) stable adsorption state semi-volatile organic pollutant extraction; (4) extracting the combined residual semi-volatile organic pollutants; and (5) measuring the content of the semi-volatile organic pollutants. According to the method, a supercritical fluid extraction technology is introduced into a traditional full-chemical continuous extraction process, so that the extraction time of water-soluble components is shortened, the damage to a soil structure in the extraction process is reduced, and the accuracy of subsequent testing is improved.

Description

Technical Field

[0001] The invention relates to the field of analysis and detection of soil pollutants, and in particular to an analysis method for semi-volatile organic pollutants in four occurrence forms in site soil. Background Art

[0002] With the rapid development of industry and agriculture in my country, the soil of the legacy sites has been polluted by organic matter to varying degrees. Semi-volatile organic compounds (SVOCs) are the main organic pollutants in the soil of these sites. They are widely sourced, highly toxic, difficult to degrade, and bioaccumulative. They exist in the soil environment for a long time and pose a potential hazard to the safety of agricultural products and human health. Typical SVOCs in soil include dioxins, polycyclic aromatic hydrocarbons, organic pesticides, chlorobenzenes, polychlorinated biphenyls, phthalates, etc. The physicochemical properties of SVOCs make them ubiquitous in various environmental media and highly mobile. SVOCs entering the atmosphere can be transported over long distances in the form of gas or aerosol, and then transferred to water bodies, sediments, soils, and plants through precipitation, particle deposition, etc. Due to their hydrophobic and lipophilic properties, SVOCs will accumulate in the soil, making the soil the final sink. Therefore, it is necessary to analyze the occurrence form and content of SVOCs in the soil of contaminated sites.

[0003] The occurrence forms of SVOCs in site soil can be divided into four forms: water-soluble, acid-soluble, stable adsorbed and bound residual. Water-soluble SVOCs mainly exist in soil solutions or attach to the surface of dissolved organic matter (DOM), and are the active components with the strongest migration and transformation capabilities. Acid-soluble SVOCs are mainly adsorbed on the surface of soil minerals and can be desorbed by plant root secretions. Stably adsorbed SVOCs are mainly adsorbed in soil organic matter (SOM), can be extracted by organic solvents, and account for the largest proportion in the soil. Bound residual SVOCs are the most stable and difficult to migrate and transform. Without destroying the soil structure, they cannot be extracted from the soil by any extractant. Water-soluble and acid-soluble SVOCs can be used by animals, plants, microorganisms, etc. under natural conditions, that is, they are bioaccessible and bioeffective, while stable adsorbed and bound residual SVOCs are difficult to be absorbed and utilized by organisms. At present, the evaluation of organic matter pollution in site soil is often based on the total concentration of organic pollutants, resulting in an overestimation of ecological and environmental risks. Therefore, it is necessary to analyze and detect the water-soluble, acid-soluble, stably adsorbed and bound residual contents of SVOCs in order to accurately assess the actual pollution level of the site and provide key parameters for the detailed calculation of soil environmental capacity.

[0004] The existing continuous extraction methods for the occurrence forms of SVOCs require a large amount of contaminated soil samples and usually use chemical extraction technology. During the continuous extraction process, the soil structure is often damaged and secondary environmental pollution is caused. The commonly used extractants for biologically effective components are HPCD or Tenax aqueous solutions, which take a long time to extract and are insoluble in organic extractants for stable adsorbed components. The drying and freeze-drying methods commonly used for soil dehydration take a long time, and during this process, SVOCs are inevitably lost through volatilization. In response to the above problems, it is necessary to improve the existing continuous extraction methods for the occurrence forms of SVOCs, reduce damage to the soil structure and the loss of SVOCs, and develop a method for efficient and accurate quantitative analysis of the content of the four occurrence forms of SVOCs in site soils. Summary of the invention

[0005] Purpose of the invention: The present invention aims to provide an efficient and accurate method for quantitatively analyzing four types of semi-volatile organic pollutants in site soil.

[0006] Technical solution: The method for analyzing four forms of semi-volatile organic pollutants in site soil of the present invention comprises the following steps:

[0007] (1) Extraction of water-soluble semi-volatile organic pollutants

[0008] The contaminated soil is mixed with anhydrous sodium sulfate, and then the water-soluble components of semi-volatile organic pollutants in the soil are extracted using a CO2 supercritical fluid extraction method, and the extract is collected for testing;

[0009] (2) Extraction of acid-soluble semi-volatile organic pollutants

[0010] The contaminated soil after the water-soluble components are extracted is added to the simulated root secretion aqueous solution, ultrasonically treated, and then solid-liquid separation is performed, the supernatant is added to the solvent for liquid-liquid extraction, and the organic phase is taken for testing after extraction;

[0011] (3) Extraction of stable adsorbed semi-volatile organic pollutants

[0012] After removing the acid-soluble components, anhydrous sodium sulfate was added to the soil, mixed until it became a quicksand state, a solvent was added, ultrasonic treatment was performed, and finally the solid and liquid were separated, and the supernatant was taken for testing;

[0013] (4) Combined with residual semi-volatile organic pollutant extraction

[0014] In the soil after removing the stable adsorbed components, after being treated by alkaline hydrolysis, the solid and liquid are separated, the supernatant is taken, a solvent is added for liquid-liquid extraction, and the organic phase is taken for testing;

[0015] (5) Determination of semi-volatile organic pollutants content

[0016] The contents of water-soluble, acid-soluble, stably adsorbed and bound residual semi-volatile organic pollutants extracted in steps (1) to (4) were determined by gas chromatography-mass spectrometry.

[0017] Step (1) uses supercritical fluid extraction technology, which shortens the extraction time of water-soluble components, reduces the damage to the soil structure during the extraction process, and improves the accuracy of subsequent detection.

[0018] In step (1), the mass of the contaminated soil is 1 to 2 g.

[0019] Preferably, in step (1), the conditions of the CO2 supercritical fluid extraction are: extraction temperature 40-50°C, extraction pressure 12-25MPa, and CO2 flow rate 1-3mL / min.

[0020] Preferably, the extraction is static extraction for 20 to 40 minutes or static extraction for 10 to 30 minutes followed by dynamic extraction for 10 to 40 minutes or dynamic extraction for 30 to 60 minutes.

[0021] Preferably, the extraction uses pure CO2 or adds methanol, acetone, acetonitrile or dichloromethane as a modified co-solvent; the collection liquid for collecting the extract is a mixture of acetone and n-hexane, or dichloromethane and n-hexane.

[0022] Preferably, after extraction in step (1), 10 mL of a mixture of acetone:n-hexane or dichloromethane:n-hexane is used as the collecting liquid; in order to replace the solvent with n-hexane, 1 mL of the collecting liquid is mixed with 5 mL of n-hexane, and nitrogen is blown to 0.25-0.5 mL in a 25° C. water bath, and the volume is fixed to 1 mL with n-hexane for testing.

[0023] Preferably, in step (2), the composition of the simulated root exudates is 1-100 mmol / L D-glucose, 1-100 mmol / L D-fructose, 1-100 mmol / L sucrose, 0.5-50 mmol / L L-malic acid, 0.5-50 mmol / L succinic acid and 0.25-25 mmol / L L-arginine, 0.25-25 mmol / L L-cysteine, and 0.25-25 mmol / L serine.

[0024] Preferably, in step (2), the solvent for the liquid-liquid extraction is n-hexane.

[0025] Preferably, in step (2), the ultrasonic time is 20 to 40 minutes, and the ultrasonic assisted extraction; the solid-liquid separation is: centrifugation at 3000 to 4000 rpm for 10 to 20 minutes; the liquid-liquid extraction is: take 5 mL of supernatant, add 5 mL of n-hexane, and oscillate at 180 to 220 rpm for 1 to 2 hours at 25°C in a constant temperature oscillating box for liquid-liquid extraction. After extraction, take 1 mL of the organic phase for testing.

[0026] In step (3), anhydrous sodium sulfate is used to dehydrate the soil during the continuous extraction process, thereby reducing the loss of SVOCs during the long drying and freeze-drying process.

[0027] Preferably, in step (3), the mass of the anhydrous sodium sulfate is 4 to 10 g.

[0028] Preferably, in step (3), the solvent is a mixture of acetone and n-hexane, or dichloromethane and n-hexane; and the amount of the solvent used is 10 mL.

[0029] Preferably, in step (3), the ultrasonic time is 20 to 40 minutes, and the ultrasonic assisted extraction; the solid-liquid separation is: centrifugation at 3000 to 4000 rpm for 10 to 20 minutes. In order to replace the solvent with n-hexane, 1 mL of the supernatant is mixed with 5 mL of n-hexane, and nitrogen is blown to 0.25 to 0.5 mL in a 25°C water bath, and the volume is fixed to 1 mL with n-hexane for testing.

[0030] Preferably, in step (4), the alkaline hydrolysis method is: adding a NaOH aqueous solution with a concentration of 1.25 to 2 mol / L, and bathing at 80 to 100° C. for 2 to 8 hours; adding HCl to acidify to a pH of less than 2, taking the supernatant after solid-liquid separation, and adding a solvent for liquid-liquid extraction; the solvent for the liquid-liquid extraction is n-hexane.

[0031] Preferably, the HCl concentration is 6 mol / L.

[0032] Preferably, the solid-liquid separation is performed by centrifugation at 3000-4000 rpm for 10-20 min.

[0033] Preferably, the liquid-liquid extraction is as follows: 5 mL of supernatant is taken, 5 mL of n-hexane is added, and the mixture is shaken at 180-220 rpm for 1-2 h at 25° C. for liquid-liquid extraction. After the extraction, 1 mL of the organic phase is taken for testing.

[0034] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: through four-step continuous extraction pre-treatment methods such as supercritical fluid extraction, ultrasound-assisted simulated root secretion extraction and organic solvent extraction, and liquid-liquid extraction after alkaline hydrolysis, combined with gas chromatography-mass spectrometry analysis technology, the water-soluble, acid-soluble, stable adsorbed and bound residual state contents of SVOCs in the site soil are detected. Compared with the existing methods, this method only requires a small amount of soil to complete continuous extraction and quantitative detection; the introduction of supercritical fluid extraction technology in the traditional full chemical continuous extraction process shortens the extraction time of water-soluble components and reduces the damage to the soil structure during the extraction process; anhydrous sodium sulfate is used to dehydrate the soil during the continuous extraction process, reducing the loss of SVOCs during long-term drying and freeze-drying. This method can efficiently and accurately quantitatively analyze the contents of the four occurrence forms of SVOCs in the site soil, so as to reasonably assess the actual pollution level and ecological and environmental risks of the site, and provide key parameters for the refined calculation of soil environmental capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the detection process of this method;

[0036] Figure 2 The standard curve diagram established by the external standard method in Example 1;

[0037] Figure 3 The soil content diagram of water-soluble, acid-soluble, stably adsorbed and bound residual CBZ in Example 1;

[0038] Figure 4 The standard curve diagram established by the external standard method for Example 2;

[0039] Figure 5 The soil content diagram of water-soluble, acid-soluble, stably adsorbed and bound residual PHE in Example 2;

[0040] Figure 6 The soil contents of water-soluble, acid-soluble, stably adsorbed CBZ and total extractable CBZ in Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below in conjunction with embodiments.

[0042] Example 1

[0043] The determination of the content of water-soluble, acid-soluble, stably adsorbed and bound residual carbazole (CBZ) in a contaminated farmland soil includes the following steps:

[0044] (1) Extraction of water-soluble CBZ

[0045] Weigh 1g of contaminated soil and mix it with 4g of anhydrous sodium sulfate and place it in the extraction kettle. Place glass fiber filter paper to prevent soil from entering the pipeline. Use pure CO2, the flow rate of CO2 is 2.5mL / min, the extraction conditions are 40℃, 12MPa, and static extraction for 40min. After extraction, use 10mL of acetone:n-hexane mixture (volume ratio 1:4) as the collection liquid. In order to replace the solvent with n-hexane, take 1mL of the collection liquid and mix it with 5mL of n-hexane, blow it to 0.5mL with nitrogen in a 25℃ water bath, and dilute it to 1mL with n-hexane for testing.

[0046] (2) Extraction of acid-soluble CBZ

[0047] The contaminated soil after extraction of water-soluble components was placed in a 30 mL glass centrifuge tube (the cap was equipped with a PTFE liner), and 10 mL of simulated root exudate aqueous solution containing 0.01 mol / L NaCl was added (the composition of the simulated root exudate was 25 mmol / L D-glucose, 25 mmol / L D-fructose, 25 mmol / L sucrose, 12.5 mmol / L L-malic acid, 12.5 mmol / L succinic acid and 6.25 mmol / L L-arginine, 6.25 mmol / L L-cysteine, 6.25 mmol / L serine), and ultrasonic-assisted extraction was performed for 40 min. After ultrasonication, centrifugation was performed at 3000 rpm for 20 min, 5 mL of supernatant was taken, 5 mL of n-hexane was added, and liquid-liquid extraction was performed in a constant temperature shaking box at 25 ° C and 220 rpm for 1 h. After extraction, 1 mL of organic phase was taken for testing.

[0048] (3) Extraction of Stably Adsorbed CBZ

[0049] After removing the acid-soluble components, add 4g of anhydrous sodium sulfate to the soil and mix it. Stir continuously until it becomes a quicksand state. Add 10mL of acetone:n-hexane mixture (volume ratio 1:4) and perform ultrasonic-assisted extraction for 40min. After ultrasonication, centrifuge at 3000rpm for 20min. In order to replace the solvent with n-hexane, take 1mL of the supernatant and mix it with 5mL of n-hexane. Blow nitrogen to 0.5mL in a 25℃ water bath and dilute to 1mL with n-hexane for testing.

[0050] (4) Combined with the extraction of residual CBZ

[0051] In the soil after removing the stable adsorbed components, the alkaline hydrolysis method was used to add 10 mL of 2 mol / L NaOH aqueous solution and water bath at 100°C for 2 hours. Acidify to pH < 2 with 6 mol / L HCl, centrifuge at 3000 rpm for 20 minutes, take 5 mL of supernatant, add 5 mL of n-hexane, and perform liquid-liquid extraction in a constant temperature oscillating box at 25°C and 220 rpm for 1 hour. After extraction, take 1 mL of organic phase for testing.

[0052] (5) Determination of CBZ content in various forms

[0053] The content of water-soluble, acid-soluble, stably adsorbed and bound residual CBZ was determined by gas chromatography-mass spectrometry (GC-MS). The chromatographic column was DB-5MS, 30 m long, 0.25 mm in inner diameter and 0.25 μm in film thickness. The gas chromatography conditions were as follows: the injection port temperature was 280 °C; no split; the temperature program was 80 °C for 2 min, and then 20 °C min -1 The rate was raised to 200°C, and then the temperature was increased at 10°C min -1 The rate was raised to 240℃, and then at 20℃·min -1 The rate was raised to 280°C and maintained for 3 min. The mass spectrometry conditions were: EI source, ion source temperature of 280°C, transfer line temperature of 280°C, solvent delay of 5 min, scan mode of selected ion scan, m / z of 167.

[0054] (6) Measurement results

[0055] Establish a standard curve such as Figure 2 As shown, the contents of water-soluble, acid-soluble, stably adsorbed and bound residual CBZ were calculated by external standard method to be 0.34 μg / g, 0.29 μg / g, 6.37 μg / g and 1.24 μg / g, respectively (as shown in Figure 3 shown).

[0056] Example 2

[0057] The determination of the content of water-soluble, acid-soluble, stably adsorbed and bound residual phenanthrene (PHE) in the soil of a chemical plant site includes the following steps:

[0058] (1) Extraction of water-soluble PHE

[0059] Weigh 1g of contaminated soil and mix it with 4g of anhydrous sodium sulfate and place it in the extraction kettle. Place glass fiber filter paper to prevent soil from entering the pipeline. Use pure CO2 with a CO2 flow rate of 2.5mL / min. The extraction conditions are 40℃, 12MPa, and static extraction for 10min followed by dynamic extraction for 30min. After extraction, use 10mL of acetone:n-hexane mixture (volume ratio 1:1) as the collection liquid. In order to replace the solvent with n-hexane, take 1mL of the collection liquid and mix it with 5mL of n-hexane. In a 25℃ water bath, blow nitrogen to 0.5mL, and dilute to 1mL with n-hexane for testing.

[0060] (2) Extraction of acid-soluble PHE

[0061] The contaminated soil after extraction of water-soluble components was placed in a 30 mL glass centrifuge tube (the cap was equipped with a PTFE liner), and 10 mL of simulated root exudate aqueous solution containing 0.05 mol / L NaCl was added (the composition of the simulated root exudate was 50 mmol / L D-glucose, 50 mmol / L D-fructose, 50 mmol / L sucrose, 25 mmol / L L-malic acid, 25 mmol / L succinic acid and 12.5 mmol / L L-arginine, 12.5 mmol / L L-cysteine, 12.5 mmol / L serine), and ultrasonic-assisted extraction was performed for 40 min. After ultrasonication, centrifugation was performed at 3000 rpm for 10 min, 5 mL of supernatant was taken, 5 mL of n-hexane was added, and liquid-liquid extraction was performed in a constant temperature shaking box at 25 ° C and 200 rpm for 1 h. After extraction, 1 mL of organic phase was taken for testing.

[0062] (3) Extraction of Stably Adsorbed PHE

[0063] After removing the acid-soluble components, add 4g of anhydrous sodium sulfate to the soil and mix it. Stir continuously until it becomes a quicksand state. Add 10mL of acetone:n-hexane mixture (volume ratio 1:1) and perform ultrasonic-assisted extraction for 40min. After ultrasonication, centrifuge at 3000rpm for 10min. In order to replace the solvent with n-hexane, take 1mL of the supernatant and mix it with 5mL of n-hexane. Blow nitrogen to 0.5mL in a 25℃ water bath and dilute to 1mL with n-hexane for testing.

[0064] (4) Combined with the extraction of residual PHE

[0065] In the soil after removing the stable adsorbed components, the alkaline hydrolysis method was used to add 10mL of 2mol / L NaOH aqueous solution and water bath at 90℃ for 2h. Acidify to pH <2 with 6mol / L HCl, centrifuge at 3000rpm for 10min, take 5mL of supernatant, add 5mL of n-hexane, and oscillate at 200rpm for 1h at 25℃ in a constant temperature oscillating box for liquid-liquid extraction. After extraction, take 1mL of organic phase for testing.

[0066] (5) Determination of PHE content in various forms

[0067] The content of water-soluble, acid-soluble, stably adsorbed and bound residual PHE was determined by gas chromatography-mass spectrometry (GC-MS). The chromatographic column was DB-5MS, 30 m long, 0.25 mm inner diameter, and 0.25 μm film thickness. Gas chromatography conditions: inlet temperature was 260 °C; no split; the temperature program was 100 °C for 2 min, 20 °C min -1The rate was raised to 290°C and maintained for 3 min. The mass spectrometry conditions were: EI source, ion source temperature of 280°C, transfer line temperature of 280°C, solvent delay of 5 min, scan mode of selected ion scan, m / z of 178.

[0068] (6) Measurement results

[0069] Establish a standard curve such as Figure 4 As shown, the contents of water-soluble, acid-soluble, stably adsorbed and bound residual PHE were calculated by external standard method to be 3.49 μg / g, 1.65 μg / g, 9.19 μg / g and 5.66 μg / g, respectively (as shown in Figure 5 shown).

[0070] Comparative Example 1

[0071] This comparative example provides a full chemical continuous extraction method. The main difference between this method and Example 1 is that the step (1) of this method uses an HPCD aqueous solution to extract water-soluble CBZ. The specific extraction method is as follows:

[0072] Weigh 1g of contaminated soil into a 30mL glass centrifuge tube (the cap is equipped with a PTFE liner), add 10mL of 50mmol / L HPCD aqueous solution, and perform ultrasonic-assisted extraction for 40min. After ultrasonication, centrifuge at 3000rpm for 20min, take 5mL of supernatant, add 5mL of n-hexane, and perform liquid-liquid extraction in a constant temperature oscillating box at 25℃ and 220rpm for 1h. After extraction, take 1mL of organic phase for testing.

[0073] The remaining steps are the same as in Example 1.

[0074] The total extractable CBZ includes water-soluble, acid-soluble and stably adsorbed CBZ. The specific extraction method is as follows:

[0075] Weigh 1g of contaminated soil and place it in a 30mL glass centrifuge tube (the cap is equipped with a PTFE liner), directly add 10mL of acetone:n-hexane mixture (volume ratio 1:4), and perform ultrasonic-assisted extraction for 40min. After ultrasonication, centrifuge at 3000rpm for 20min. In order to replace the solvent with n-hexane, take 1mL of supernatant and mix it with 5mL of n-hexane, blow it to 0.5mL with nitrogen in a 25℃ water bath, and dilute it to 1mL with n-hexane for testing.

[0076] The test results are as follows Figure 6 shown.

[0077] Depend on Figure 6It can be obtained that the total extractable CBZ content in the contaminated soil is 6.83μg / g; in Example 1, the measured water-soluble, acid-soluble and stable adsorbed CBZ contents are 0.34μg / g, 0.29μg / g and 6.37μg / g, respectively, totaling 7μg / g; in Comparative Example 1, the water-soluble, acid-soluble and stable adsorbed CBZ contents measured using the full chemical continuous extraction method are 0.36μg / g, 0.22μg / g, 2.71μg / g, respectively, totaling 3.29μg / g. The results show that the water-soluble, acid-soluble and stable adsorbed CBZ contents measured by this method are closer to the total extractable CBZ content in the contaminated soil, indicating that this method introduces supercritical fluid extraction technology in the traditional full chemical continuous extraction process, while shortening the extraction time of water-soluble components, by reducing the damage to the soil structure during the extraction process, the accuracy of subsequent tests is improved.

Claims

1. A method for analyzing four forms of semi-volatile organic pollutants in site soil, characterized in that: The following steps are involved: (1) Extraction of water-soluble semi-volatile organic pollutants The contaminated soil is mixed with anhydrous sodium sulfate, and then the water-soluble components of semi-volatile organic pollutants in the soil are extracted using a CO2 supercritical fluid extraction method, and the extract is collected for testing; (2) Extraction of acid-soluble semi-volatile organic pollutants The contaminated soil after the water-soluble components are extracted is added to the simulated root secretion aqueous solution, ultrasonically treated, and then solid-liquid separation is performed, the supernatant is added to the solvent for liquid-liquid extraction, and the organic phase is taken for testing after extraction; (3) Extraction of stable adsorbed semi-volatile organic pollutants After removing the acid-soluble components, anhydrous sodium sulfate was added to the soil, mixed until it became a quicksand state, a solvent was added, ultrasonic treatment was performed, and finally the solid and liquid were separated, and the supernatant was taken for testing; (4) Combined with residual semi-volatile organic pollutant extraction In the soil after removing the stable adsorbed components, after being treated by alkaline hydrolysis, the solid and liquid are separated, the supernatant is taken, a solvent is added for liquid-liquid extraction, and the organic phase is taken for testing; (5) Determination of semi-volatile organic pollutants content The contents of water-soluble, acid-soluble, stably adsorbed and bound residual semi-volatile organic pollutants extracted in steps (1) to (4) were determined by gas chromatography-mass spectrometry.

2. The method for analyzing four types of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: In step (1), the mass of the contaminated soil is 1 to 2 g.

3. The method for analyzing four types of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: In step (1), the conditions of the CO2 supercritical fluid extraction are: extraction temperature 40-50°C, extraction pressure 12-25MPa, and CO2 flow rate 1-3mL / min.

4. The method for analyzing four forms of semi-volatile organic pollutants in site soil according to claim 3, characterized in that: The extraction is static extraction for 20 to 40 minutes or static extraction for 10 to 30 minutes followed by dynamic extraction for 10 to 40 minutes or dynamic extraction for 30 to 60 minutes.

5. The method for analyzing four types of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: The extraction uses pure CO2 or adds methanol, acetone, acetonitrile or dichloromethane as a modified co-solvent; the collection liquid for collecting the extract is a mixture of acetone and n-hexane, or dichloromethane and n-hexane.

6. The method for analyzing four forms of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: In step (2), the composition of the simulated root exudates is 1-100 mmol / L D-glucose, 1-100 mmol / L D-fructose, 1-100 mmol / L sucrose, 0.5-50 mmol / L L-malic acid, 0.5-50 mmol / L succinic acid and 0.25-25 mmol / L L-arginine, 0.25-25 mmol / L L-cysteine, and 0.25-25 mmol / L serine.

7. The method for analyzing four forms of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: In step (2), the solvent for the liquid-liquid extraction is n-hexane.

8. The method for analyzing four forms of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: In step (3), the mass of the anhydrous sodium sulfate is 4 to 10 g.

9. The method for analyzing four forms of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: In step (3), the solvent is a mixture of acetone and n-hexane, or dichloromethane and n-hexane.

10. The method for analyzing four forms of semi-volatile organic pollutants in site soil according to claim 1, characterized in that: In step (4), the alkaline hydrolysis method is: adding a NaOH aqueous solution with a concentration of 1.25 to 2 mol / L, and bathing at 80 to 100° C. for 2 to 8 hours; adding HCl to acidify to a pH of less than 2, taking the supernatant after solid-liquid separation, and adding a solvent for liquid-liquid extraction; the solvent for the liquid-liquid extraction is n-hexane.

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