A method for detecting nmp in soil

Abstract

This invention relates to the field of compound analysis and detection, and more specifically to a method for detecting NMP in soil. The method includes sample pretreatment, extraction, purification, concentration, and LC-MS / MS detection: soil samples are purified, coarsely separated using a quartering method, freeze-dried for dehydration, ground, sieved, and homogenized; extracted with deionized water, the supernatant is collected by low-speed shaking and high-speed centrifugation; purified using an HLB solid-phase extraction column activated with methanol and water, concentrated and diluted to volume with nitrogen blowing before detection. Chromatography uses a C18 column with a trapping column, eluted with formic acid-water and formic acid-acetonitrile gradients; mass spectrometry uses electrospray ionization in positive ion mode with multiple reaction monitoring, using a precursor ion of 100, a quantitative product ion of 58.1, and a qualitative product ion of 69.1 for qualitative and quantitative analysis. This method avoids target analyte loss, reduces matrix interference and background contamination, has high sensitivity, accurate qualitative analysis, and stable recovery rate (98.9% spiked recovery), filling the gap in domestic methods for the dedicated detection of NMP in soil, and is suitable for site investigations and environmental monitoring.

Description

Technical Field

[0001] This invention relates to the field of compound analysis and detection, and more specifically to a method for detecting NMP in soil. Background Technology

[0002] NMP (1-methyl-2-pyrrolidone) is a highly polar, low-volatility, and extremely potent aprotic polar solvent. Due to its excellent chemical stability and solubility, NMP is widely used in industries such as electronic chemicals, pharmaceutical intermediates, polymer synthesis, coatings, and cleaning agents. With the rapid development of related industries, the production, use, disposal, and transportation of NMP are increasing, leading to a continuous rise in the risk of leakage and discharge in production workshops, wastewater treatment plants, industrial sites, and surrounding areas. Because of its strong water solubility and mobility, NMP easily leaches into the soil with rainwater after entering the environment, adsorbing and migrating between soil particles, and even infiltrating downwards to contaminate groundwater. Related studies have shown that NMP can have potentially adverse effects on soil microbial activity, enzyme systems, and plant and animal growth. Long-term residues may also enter the human body through the food chain, threatening ecological security and human health. Therefore, accurate, sensitive, and reliable detection of NMP in soil is an important prerequisite for conducting industrial site investigations, soil pollution risk assessments, and pollution remediation effectiveness evaluations.

[0003] Currently, there is considerable research on the detection of NMP in matrices such as water, air, and food, with commonly used methods including gas chromatography, gas chromatography-mass spectrometry, and high-performance liquid chromatography. However, mature analytical techniques suitable for soil matrices are clearly insufficient. Soil matrices have complex compositions, containing humic acids, heavy metals, pigments, lipids, and various organic interfering substances, which can significantly inhibit the response of target analytes, reduce separation, and affect quantitative accuracy. Traditional pretreatment methods often employ organic solvent shaking, Soxhlet extraction, or ultrasonic extraction, which not only consume large amounts of organic solvents and easily introduce background contamination, but also suffer from low extraction efficiency and significant loss of target analytes. Conventional purification methods are insufficient to effectively remove soil matrix interferences, resulting in low recovery rates and poor repeatability of detection results.

[0004] Given the complexities of soil sample pretreatment, strong matrix interference, easy loss of target analytes, and the lack of dedicated detection methods, the development of efficient, green, sensitive, and stable analytical techniques has become an urgent need. Traditional natural drying or heat drying easily leads to NMP volatilization loss; conventional liquid chromatography has low sensitivity and weak qualitative ability; while gas chromatography requires derivatization, which is cumbersome and time-consuming. Therefore, there is an urgent need to establish a complete analytical method to overcome the shortcomings of existing technologies in soil NMP detection, and to provide reliable technical support for industrial contaminated site monitoring, soil environmental quality assessment, and ecological risk management. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for detecting NMP in soil, comprising the following steps: S1. Remove impurities from the soil to be tested, perform coarse separation using the quartering method, and then freeze dry the soil using a freeze dryer. Grind, sieve, and homogenize the freeze-dried sample to obtain the sample to be extracted. S2. Add the sample to be extracted into a centrifuge tube, add deionized water, shake at low speed first, then centrifuge at high speed, take the supernatant and filter it. S3. Activate the HLB solid-phase extraction column, load the filtered supernatant through the HLB solid-phase extraction column, wash the HLB solid-phase extraction column after loading, and then elute and collect the eluent. S4. Concentrate the eluent using a nitrogen blower, then add deionized water to make up the volume, and use LC-MS / MS (liquid chromatography / triple tandem quadrupole mass spectrometry) to detect the NMP content.

[0006] This invention employs freeze-drying dehydration, grinding and homogenization pretreatment, deionized water extraction, HLB solid-phase extraction column purification and impurity removal, nitrogen blowing concentration and volume fixation, combined with LC. MS / MS detection in MRM mode can effectively solve a series of technical problems in soil NMP, such as easy volatilization loss under traditional drying methods, high background pollution and unstable recovery rate caused by organic solvent extraction, poor peak shape and inaccurate quantification due to the presence of many interfering substances such as humic acid in the soil matrix, insufficient sensitivity and unreliable qualitative analysis of conventional detection methods, and the lack of a dedicated standard detection method for NMP in soil in China. It significantly improves the recovery rate of target analytes, detection accuracy and method stability, and can realize accurate qualitative and quantitative detection of trace NMP in soil.

[0007] This invention employs freeze-drying dehydration to dehydrate soil samples under mild conditions of low temperature and vacuum, avoiding the volatilization, decomposition, and loss of NMP caused by traditional air drying and heating methods. At the same time, it maximizes the preservation of the original components and stability of the target substances in the soil sample, preventing changes in the sample's properties due to high temperature or prolonged oxidation. This provides a uniform, stable sample for subsequent extraction, purification, and detection without loss of target substances, ensuring the accuracy, repeatability, and recovery rate of the detection results from the source.

[0008] As an feasible example, the quartering method described herein is implemented in accordance with HJ / T166 "Technical Specification for Soil Environmental Monitoring". In this invention, if the moisture content of the sample after coarse separation is greater than 30%, centrifugation is required to separate out a portion of the aqueous phase, which can effectively improve the processing efficiency of freeze-drying dehydration.

[0009] As an example of implementation, the low-speed oscillation is performed at a rotation speed of 500-800 rpm, with a processing time of 5-20 minutes.

[0010] As an example of implementation, the high-speed centrifugation speed is 5000-8000 rpm, and the processing time is 1-5 min.

[0011] This invention limits the rotation speed and time range of low-speed oscillation and high-speed centrifugation. This ensures that the highly water-soluble NMP in the soil is fully and gently extracted into the aqueous phase, guaranteeing complete release of the target compound and stable extraction efficiency. It also avoids excessively high rotation speeds and long times, which could lead to the dissolution of large amounts of soil colloids, humic acids, and other impurities, increasing matrix interference. Simultaneously, it prevents insufficient extraction of the target compound and inadequate clarity of the supernatant due to excessively low rotation speeds and short times. The synergistic combination of low-speed oscillation at 500-800 rpm for 5-20 min and high-speed centrifugation at 5000-8000 rpm for 1-5 min rapidly yields a clear supernatant with minimal impurities and target compound loss, providing a suitable environment for subsequent solid-phase extraction purification and LC. MS / MS precision detection provides a stable and reliable sample system, effectively improving the recovery rate, repeatability, and detection accuracy of the method.

[0012] As an example of an feasible approach, the activation treatment includes deionized water activation and methanol activation.

[0013] This invention limits the activation treatment to methanol activation and deionized water activation. First, the HLB solid-phase extraction column is wetted and activated with methanol to fully expand the hydrophobic groups of the packing material and maintain optimal adsorption activity. Then, deionized water is used for equilibration and transition to ensure that the extraction column environment is consistent with the aqueous sample system loaded subsequently. This avoids the loss of target substances due to sudden changes in solvent polarity, and effectively removes residual impurities and air bubbles in the packing material. This ensures a stable flow rate during the loading process and that the target substances are fully retained and enriched, providing a stable and reliable purification basis for subsequent elution, elution, and accurate quantification, thereby improving the repeatability and recovery rate of the method.

[0014] As an example of implementation, the flow rate for loading the supernatant is 0.5-1 mL / min.

[0015] As an example of an implementable procedure, the rinsing process includes rinsing with deionized water and rinsing with methanol.

[0016] Furthermore, the flow rates of both the deionized water rinsing and the methanol rinsing are 0.5-1 mL / min.

[0017] This invention limits the rinsing process to deionized water rinsing and methanol rinsing, and controls the flow rate at 0.5-1 mL / min. The purpose is to first use deionized water rinsing to remove inorganic salts, polar impurities, and some water-soluble matrix interferences from the sample, and then use a low-proportion methanol rinsing to further remove weakly polar interferences. This maximizes sample purification without losing the target analyte NMP. Simultaneously, strictly controlling the flow rate at 0.5-1 mL / min ensures sufficient contact between the rinsing solution and the packing material, complete elution of impurities, and avoids incomplete rinsing due to excessively high flow rates or prolonged pretreatment time due to excessively slow flow rates. This effectively reduces matrix effects, improves chromatographic peak shape, enhances detection sensitivity and quantitative accuracy, and ensures method recovery and stability.

[0018] As an implementable example, in the LC-MS / MS described above, the mobile phase A of the liquid chromatography is formic acid-water solution, and the mobile phase B is formic acid-acetonitrile solution.

[0019] Furthermore, the liquid chromatography employs gradient elution: for 0-2 min, the volume ratio of mobile phase A to mobile phase B is 98:2; for 2-3.5 min, the volume ratio of mobile phase A to mobile phase B is 95:5; for 3.5-5 min, the volume ratio of mobile phase A to mobile phase B is 85:15; for 5-7 min, the volume ratio of mobile phase A to mobile phase B is 10:90; and after 7 min, the volume ratio of mobile phase A to mobile phase B is 95:5.

[0020] The process involves maintaining a high aqueous phase ratio for 0-2 minutes to ensure effective retention of the highly polar target analyte NMP on the column. From 2-5 minutes, the organic phase ratio is gradually increased to achieve good separation of the target analyte from matrix interferences. From 5-7 minutes, the organic phase ratio is significantly increased to rapidly elute residual, highly retained impurities and clean the column. After 7 minutes, the ratio is rapidly restored to a high aqueous phase to complete column equilibration. Throughout the process, the method ensures symmetrical NMP peak shape, excellent resolution, and no matrix interference, while also achieving rapid target analyte elution, short detection cycle, and stable column life, ultimately improving the sensitivity, repeatability, and quantitative accuracy of the method.

[0021] As an example of implementation, the packing material for both the chromatographic column and the trapping column of the liquid chromatography is octadecylsiloxane.

[0022] This invention limits both the chromatographic column and the trapping column to octadecylsiloxane (C18) packing material. C18 is the most universal and stable stationary phase in reversed-phase chromatography, and it has suitable retention capacity for highly polar NMP, ensuring symmetrical peak shape and good resolution of the target analyte. At the same time, using the same C18 packing material for both the chromatographic column and the trapping column can maintain the consistency of the properties of the two stationary phases, avoiding peak splitting, broadening, or retention time drift caused by differences in packing material. This effectively reduces matrix effects, eliminates interference caused by dead volume in the system, improves the repeatability and qualitative and quantitative accuracy of the detection, and can also extend the service life of the chromatographic column, ensuring long-term stability and reproducibility of the method.

[0023] As an feasible example, in the LC-MS / MS described above, the ion source for mass spectrometry is an electrospray ion source, and the monitoring method is multiple reaction monitoring (MRM).

[0024] Furthermore, the conditions for the multiple reaction monitoring are as follows: precursor ion 100, quantitative daughter ion 58.1, declustering voltage 60V, collision voltage 26V, collision chamber outlet voltage 14V; qualitative daughter ion 69.1, declustering voltage 60V, collision voltage 42V, collision chamber outlet voltage 10V.

[0025] This invention precisely defines the conditions for multiple reaction monitoring (MRM), providing NMP with dedicated, stable, and highly sensitive mass spectrometry detection parameters. It achieves precise screening of target analytes through the precursor ion 100, and forms two sets of characteristic ion pairs with quantitative ion 58.1 and qualitative ion 69.1. Under corresponding declustering voltage, collision voltage, and collision chamber exit voltage, it obtains the strongest ion response and optimal signal-to-noise ratio. This ensures accurate and reliable quantitative results with strong resistance to matrix interference, while also enabling rigorous qualitative determination through the dual ion pair ratio, effectively avoiding false positives. Ultimately, it achieves highly sensitive, specific, and accurate detection of trace NMP in soil.

[0026] Beneficial effects (i) This invention uses freeze-drying to pretreat soil samples. Dehydration is completed under low temperature and vacuum conditions, avoiding the volatilization, decomposition and loss of NMP caused by traditional heating and drying or natural air drying. At the same time, grinding and sieving are combined to achieve sample homogenization, reduce the error caused by matrix inhomogeneity from the source, effectively improve the recovery rate of target substances and the accuracy of detection results, and ensure the stability and reliability of the method.

[0027] (II) This invention employs deionized water extraction combined with HLB solid-phase extraction purification. First, aqueous extraction is used to match the strong water solubility of the target analytes, reducing background pollution introduced by organic solvents. Then, methanol-water activation, water rinsing to remove impurities, and methanol elution enrichment can efficiently remove interfering substances such as humic acid, pigments, and lipids from the soil, significantly reducing matrix effects, improving chromatographic peak shape, and enhancing separation and detection sensitivity, making it suitable for complex soil matrix analysis.

[0028] (III) This invention employs LC-MS / MS multiple reaction monitoring mode, setting the precursor ion to 100, the quantitative daughter ion to 58.1, and the qualitative daughter ion to 69.1, and matching dedicated declustering voltage, collision voltage, and collision chamber outlet voltage to form a dedicated "mass spectroscopic fingerprint" for the target analyte. Dual ion pair monitoring can strictly meet the requirements for qualitative determination, effectively eliminate the influence of interfering substances, achieve accurate qualitative and quantitative analysis of trace NMP, and significantly reduce the risk of false positives.

[0029] (iv) This invention optimizes key parameters such as low-speed oscillation, high-speed centrifugation, nitrogen blowing concentration, and gradient elution to achieve efficient integration of pretreatment and detection processes, eliminating the need for complex derivatization operations and shortening the overall analysis time. The parameters such as oscillation, centrifugation, rinsing, and elution have clear and controllable ranges, good operational repeatability, and are suitable for rapid detection of large batches of soil samples, meeting the needs of scenarios such as industrial site investigation, soil environmental monitoring, and risk assessment.

[0030] (V) This invention addresses the lack of NMP detection technology in soil and the poor applicability of existing methods by constructing a complete and proprietary analytical method, filling the gap in the domestic lack of standard detection methods for this substance in soil. The method is environmentally friendly, highly sensitive, accurate, and stable, providing reliable technical support for soil pollution monitoring, ecological risk assessment, and pollution remediation and control, and has good prospects for widespread application. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the NMP chromatographic peaks in Application Example 1.

[0032] Figure 2 This is a schematic diagram of the NMP chromatographic peaks for Comparative Example 1.

[0033] Figure 3 This is a schematic diagram of the NMP chromatographic peaks for Comparative Example 2.

[0034] Figure 4 This is a schematic diagram of the NMP chromatographic peaks for Comparative Example 3. Detailed Implementation

[0035] Example 1 This example provides a method for detecting NMP in soil, including the following steps: S1. Place the soil to be tested on an enamel plate, mix well, remove foreign objects such as branches, leaves, and stones, and perform coarse separation using the quartering method according to HJ / T166 "Technical Specification for Soil Environmental Monitoring". Then, use a freeze dryer to freeze dry and dehydrate the sample. Grind the freeze-dried sample, sieve it, and homogenize it into particles with a particle size of about 0.25 mm to obtain the sample to be extracted. S2. Add 5.00g of the sample to be extracted to a 50mL centrifuge tube, add 20mL of deionized water, and use a shaker to shake the centrifuge tube at a low speed of 600rpm for 10min, and then centrifuge at a high speed of 8000rpm for 3min. Take the supernatant and filter it. S3. Activate the HLB solid-phase extraction column with 5 mL of methanol and 5 mL of deionized water in sequence. Take 5.0 mL of the filtered supernatant and load it onto the HLB solid-phase extraction column at a flow rate of 1 mL / min. After loading, wash the HLB solid-phase extraction column with 5 mL of deionized water and 5 mL of methanol in sequence at a flow rate of 1 mL / min. Then elute and collect the eluent. S4. Concentrate the eluent to 0.1 mL using a nitrogen blower, then add deionized water to bring the volume to 1.0 mL. Detect the NMP content using LC-MS / MS.

[0036] In the LC-MS / MS described above, the mobile phase A of the liquid chromatography is a formic acid-water solution (formic acid mass concentration of 1 wt%), and the mobile phase B is a formic acid-acetonitrile solution (formic acid mass concentration of 1 wt%).

[0037] The liquid chromatography described herein uses gradient elution, with mobile phase A:mobile phase B = 98:2 (v / v) from 0 to 2 min. At 2-3.5 min, the volume ratio of mobile phase A to mobile phase B is 95:5; At 3.5-5 min, the volume ratio of mobile phase A to mobile phase B is 85:15. At 5-7 min, the volume ratio of mobile phase A to mobile phase B is 10:90; After 7 minutes, the volume ratio of mobile phase A to mobile phase B is 95:5.

[0038] Flow rate: 0.3 mL / min; Column temperature: 30℃; Injection volume: 2 μL; Chromatographic column: The packing material is octadecylsiloxane with a particle size of 2.6 μm, a column length of 100 mm, and an inner diameter of 2.1 mm; The trapping column is filled with octadecylsiloxane with a particle size of 2.6 μm, a column length of 50 mm, and an inner diameter of 2.1 mm.

[0039] In the aforementioned LC-MS / MS, the mass ion source is an electrospray ion source, using positive ion mode, and the monitoring method is multiple reaction monitoring.

[0040] Air curtain pressure: 35.0 psi; Spray voltage: 4500V; Atomization temperature: 550℃; Atomizer pressure: 55 psi; Auxiliary gas pressure: 60 psi; The multiple reaction monitoring conditions for the target compound NMP are shown in Table 1.

[0041] Table 1

[0042] 1. Establishment of the standard curve 1.1 Preparation of the standard series: Accurately measure 0.05 mL, 0.10 mL, 0.20 mL, 0.50 mL, 1.0 mL, and 2.0 mL of NMP standard working solution (ρ=100 μg / L), dilute with water to a final volume of 10 mL, and obtain a series of standard solutions with NMP mass concentrations of 0.5 ng / mL, 1.0 ng / mL, 2.0 ng / mL, 5.0 ng / mL, 10.0 ng / mL, and 20.0 ng / mL, respectively, for LC-MS / MS determination.

[0043] 1.2 Establishment of the standard curve: A standard curve is established with the mass concentration of the target compound NMP as the abscissa and its corresponding response value as the ordinate.

[0044] 1.3. Sample Determination: The sample shall be determined under the same instrument conditions as the standard curve determination. If the concentration exceeds the linear range of the standard curve, the sample size should be appropriately reduced, and the sample should be prepared again according to the sample preparation procedure and then determined.

[0045] 1.4 Blank test: The blank sample shall be tested under the same instrument conditions as the sample test.

[0046] 2. Qualitative Analysis Monitoring is performed according to the parent and daughter ions determined in the mass spectrometry reference conditions.

[0047] The absolute value of the relative deviation between the retention time of the target compound NMP in the sample and the retention time of the target compound in the standard solution should be less than 2.5%; and the relative abundance of the qualitative ion of the target compound in the sample should be compared with the relative abundance of the corresponding qualitative ion in the standard solution with a similar concentration. If the deviation is within ±25%, it can be determined that the corresponding target compound exists in the sample. and are calculated according to formulas (1) and (2) respectively.

[0048] (1) In the formula: K sam —Relative abundance of the target compound's qualitative ions in the sample, % A 2—Peak area (or peak height) of the target compound qualitative ion pair in the sample; A 1 — Peak area (or peak height) of the quantitative ion pair of the target compound in the sample.

[0049] (2) In the formula: K std —Relative abundance of the target compound's qualitative ions in the standard solution, % A std2 —Peak area (or peak height) of the target compound's qualitative ion pair in the standard solution; A std1 —Peak area (or peak height) of the quantitative ion pair of the target compound in the standard solution.

[0050] b. Result Calculation The concentration of NMP in the sample is calculated according to formula (3).

[0051] (3) In the formula: w —NMP concentration in soil samples, μg / kg; ρ — The mass concentration of NMP calculated from the standard curve, in μg / L; V 1 — The final volume of the sample, mL; V 2 — Extraction volume, mL; V 3—Volume of extract during purification, mL; m —The mass of the soil sample taken, in grams; ω dm —Dry matter content of the sample,%.

[0052] Application Example 1 Following the experimental testing method disclosed in Example 1, standards were prepared. 5.00 ng of NMP standard was added to 5.00 g of soil sample. The sample pretreatment was performed according to the above steps. Six parallel samples were prepared and measured using the above method, and the accuracy was calculated. The results are shown in Table 2. A schematic diagram of the NMP chromatographic peaks is shown below. Figure 1 As shown.

[0053] Table 2

[0054] From Table 2 and Figure 1The experimental results show that, using 5 ng of NMP as the spiking amount, six parallel spiked recovery experiments were conducted on blank soil samples with an original sample concentration of ND (not detected). The measured sample concentrations were 4.37 ng, 4.15 ng, 3.93 ng, 3.81 ng, 4.42 ng, and 4.55 ng, with recoveries of 87.4%, 83.0%, 78.6%, 76.2%, 88.4%, and 91.0%, respectively, and an average of 4.21 ng, corresponding to an average recovery rate of 84.1%. The experimental results indicate that the method of this invention achieves a recovery rate of over 70% for NMP in soil, with low loss during the extraction and purification process. The data distribution is generally concentrated with no significant abnormal deviations, indicating good precision, high stability, and strong repeatability. Furthermore, the original sample being ND proves that the blank matrix is ​​free from target interference, resulting in a clean detection background. The method demonstrates outstanding resistance to matrix interference and can accurately quantify trace NMP in soil, meeting the accuracy and precision requirements of environmental testing. This fully validates the scientific, reliable, and practical nature of this analytical method.

[0055] Comparative Example 1 The specific implementation method in this example is the same as in Example 1, except that the soil to be tested was not freeze-dried and dehydrated.

[0056] In this example, because freeze-drying dehydration was not performed, the accuracy of the NMP test results was significantly reduced. See the test chromatograms for details. Figure 2 .

[0057] Comparative Example 2 The specific implementation method in this example is the same as in Example 1, except that the HLB solid-phase extraction column was not eluted after the sample loading was completed.

[0058] In this example, because no elution was performed after sample loading, the peak shape of the target analyte NMP peak will be severely deteriorated, and the resolution will not achieve the desired result. See the test chromatogram for details. Figure 3 .

[0059] Comparative Example 3 The specific implementation method of this example is the same as that of Example 1, except that the deionized water in step S2 is replaced with the organic solvent methanol.

[0060] In this example, the use of organic solvents for extraction can lead to uncontrollable contamination in the sample, affecting the actual sample recovery rate. See the test chromatograms for details. Figure 4 .

Claims

1. A method for detecting NMP in soil, characterized in that, Includes the following steps: S1. Remove impurities from the soil to be tested, perform coarse separation using the quartering method, and then freeze dry the soil using a freeze dryer. Grind, sieve, and homogenize the freeze-dried sample to obtain the sample to be extracted. S2. Add the sample to be extracted into a centrifuge tube, add deionized water, shake at low speed first, then centrifuge at high speed, take the supernatant from the upper layer, and filter it. S3. Activate the HLB solid-phase extraction column, load the filtered supernatant onto the HLB solid-phase extraction column, and after loading, wash the HLB solid-phase extraction column, then elute and collect the eluent. S4. Concentrate the eluent using a nitrogen blower, then bring it to a final volume using deionized water, and determine the NMP content using LC-MS / MS.

2. The method for detecting NMP in soil according to claim 1, characterized in that, The low-speed oscillation has a rotation speed of 500-800 rpm and a processing time of 5-20 min.

3. The method for detecting NMP in soil according to claim 1, characterized in that, The high-speed centrifuge operates at a speed of 5000-8000 rpm and a processing time of 1-5 minutes.

4. The method for detecting NMP in soil according to claim 1, characterized in that, The activation treatment includes deionized water activation and methanol activation.

5. The method for detecting NMP in soil according to claim 1, characterized in that, The rinsing process includes rinsing with deionized water and rinsing with methanol.

6. The method for detecting NMP in soil according to claim 5, characterized in that, The flow rates for both the deionized water rinsing and the methanol rinsing are 0.5-1 mL / min.

7. The method for detecting NMP in soil according to claim 1, wherein in the LC-MS / MS, the mobile phase A of the liquid chromatography is formic acid-water solution, and the mobile phase B is formic acid-acetonitrile solution.

8. The method for detecting NMP in soil according to claim 7, characterized in that, The liquid chromatography described herein uses gradient elution, with a mobile phase A:mobile phase B volume ratio of 98:2 during the first 0-2 minutes. At 2-3.5 min, the volume ratio of mobile phase A to mobile phase B is 95:5; At 3.5-5 min, the volume ratio of mobile phase A to mobile phase B is 85:

15. At 5-7 min, the volume ratio of mobile phase A to mobile phase B is 10:90; After 7 minutes, the volume ratio of mobile phase A to mobile phase B is 95:

5.

9. The method for detecting NMP in soil according to claim 1, characterized in that, In the aforementioned LC-MS / MS, the ion source for mass spectrometry is an electrospray ion source, and the monitoring method is multiple reaction monitoring.

10. The method for detecting NMP in soil according to claim 9, characterized in that, The conditions for the multiple reaction monitoring are as follows: mother ion 100, quantitative daughter ion 58.1, declustering voltage 60V, collision voltage 26V, collision chamber outlet voltage 14V; qualitative daughter ion 69.1, declustering voltage 60V, collision voltage 42V, collision chamber outlet voltage 10V.

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