Methods for determining imidacloprid and fipronil and their metabolites

Abstract

This invention discloses a method for determining imidacloprid and fipronil and their metabolites, comprising the following steps: (1) using liquid chromatography in tandem triple quadrupole to detect a liquid sample containing at least one of imidacloprid and fipronil and their metabolites, wherein the mobile phases used in the liquid chromatography are: aqueous phase A: an aqueous solution containing 0.5–4 mM ammonium formate and 0.005–0.02% formic acid; organic phase B: a methanol solution containing 0.5–4 mM ammonium formate and 0.005–0.02% formic acid; (2) determining the content of each compound according to the standard curve of each compound. This method requires a small sample size, simple pretreatment, and a small amount of organic reagents, and can simultaneously detect 10 compounds of two pesticides, imidacloprid and fipronil, and their metabolites.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry and relates to a method for determining imidacloprid and fipronil and their metabolites, and more particularly to a method for determining imidacloprid and fipronil and their metabolites in soil using LC-MS / MS. Background Technology

[0002] Pesticide residues refer to the amount of pesticides and their toxic metabolites remaining in plants, soil, and the environment after pesticide application. Imidacloprid and fipronil are commonly used nitromethylene insecticides that are toxic, easily remain in plants, and accumulate through the food chain, leading to environmental pollution and harming human health. To ensure environmental and food safety, establishing rapid and reliable methods for detecting imidacloprid and fipronil is of great significance for protecting public health.

[0003] Existing methods for detecting imidacloprid and fipronil residues in soil require large sample sizes for pretreatment, typically 10g of soil, and large amounts of extraction solvents, usually more than 20mL, to extract imidacloprid, fipronil, and their metabolites from the soil, which is time-consuming and labor-intensive. Summary of the Invention

[0004] To provide a rapid and convenient mass spectrometry method for screening the residues of two pesticides, imidacloprid and fipronil, and their metabolites in the environment (such as soil), and to offer a reliable basis for environmental assessment, the inventors have explored and experimented with detection methods for imidacloprid and fipronil and their metabolites, finding a technique that requires small sample sizes and consumes minimal solvents, especially organic solvents. Specifically, this invention includes the following technical solutions.

[0005] A method for determining imidacloprid (IMI), fipronil (DIN), or their metabolites, comprising the following steps:

[0006] (1) Liquid samples containing at least one of imidacloprid (IMI) and fipronil (DIN) and their metabolites were detected by liquid chromatography-tandem triple quadrupole mass spectrometry (LC-MS / MS);

[0007] The mobile phases used in the liquid chromatography are as follows: Aqueous phase A: an aqueous solution containing 0.5–4 mM, preferably 1–3.5 mM, preferably 1.2–3.2 mM, preferably 1.5–3 mM, preferably 1.8–2.5 mM, most preferably about 2 mM ammonium formate and 0.005–0.02%, preferably 0.008–0.015%, most preferably about 0.01% formic acid; Organic phase B: a methanol solution containing 0.5–4 mM, preferably 1–3.5 mM, preferably 1.2–3.2 mM, preferably 1.5–3 mM, preferably 1.8–2.5 mM, most preferably about 2 mM ammonium formate and 0.005–0.02%, preferably 0.008–0.015%, most preferably about 0.01% formic acid.

[0008] In mass spectrometry detection, two ion channels are selected for each compound: one quantitative ion channel and the other qualitative ion channel. The quantitative and qualitative ion channels for imidacloprid are m / z 256 > 209 and m / z 256 > 175, respectively; the quantitative and qualitative ion channels for fipronil are m / z 203 > 113 and m / z 203 > 157, respectively.

[0009] (2) Determine the content of each compound based on the standard curve of each compound.

[0010] Preferably, in step (1) above, the aqueous phase A is an aqueous solution containing approximately 2 mM ammonium formate and approximately 0.01% formic acid; and the organic phase B is a methanol solution containing approximately 2 mM ammonium formate and approximately 0.01% formic acid.

[0011] The metabolites of imidacloprid are selected from the following compounds: 1-[(6-chloropyridin-3-yl)methyl]-1-nitroguanidine, imidacloprid-guanidine hydrochloride, imidacloprid olefin, imidacloprid urea, 6-hydroxynicotinic acid, and 6-chloronicotinic acid; the metabolites of fipronil are selected from the following compounds: 1-methyl-3-[(3-tetrahydrofuran)methyl]urea and 1-methyl-3-[(3-tetrahydrofuran)methyl]dihydroguanidine salt.

[0012] Among them, the quantitative ion channel and the qualitative ion channel of 1-[(6-chloropyridin-3-yl)methyl]-1-nitroguanidine are m / z 230 > 186 and m / z 230 > 148, respectively;

[0013] The quantitative and qualitative ion channels of imidacloprid-guanidine hydrochloride are m / z 211 > 126 and m / z 211 > 90, respectively.

[0014] The quantitative and qualitative ion channels of imidacloprid olefin are m / z 254 > 205 and m / z 254 > 171, respectively.

[0015] The quantitative and qualitative ion channels of imidacloprid are m / z 212 > 128 and m / z 212 > 99, respectively.

[0016] The quantitative and qualitative ion channels for 6-hydroxynicotinic acid are m / z 140 > 122 and m / z 140 > 78, respectively.

[0017] The quantitative and qualitative ion channels for 6-chloronicotinic acid are m / z 158 > 122 and m / z 160 > 122, respectively.

[0018] The quantitative and qualitative ion channels for 1-methyl-3-[(3-tetrahydrofuran)methyl]urea are m / z 159 > 102 and m / z 159 > 67, respectively.

[0019] The quantitative and qualitative ion channels of 1-methyl-3-[(3-tetrahydrofuran)methyl]dihydroguanidine salt are m / z 158>102 and m / z 158>57, respectively.

[0020] The sources of the liquid samples mentioned above can be selected from the following groups: plant matter such as rice, soil, and aquatic environment.

[0021] In one embodiment, the source of the liquid sample to be tested is soil, and the extraction of the liquid sample may include, for example, the following steps:

[0022] (a) Prepare a mixed solvent of acetonitrile:water (v / v) = 1:0.5-1.5, preferably 1:0.8-1.2, preferably 1:0.9-1.2, most preferably about 1:1, and add 3-8%, preferably 3.5-7%, preferably 4-6%, most preferably 5% formic acid to obtain the extraction solvent;

[0023] (b) Add the extraction solvent obtained in step (a) to the freeze-dried soil at a volume / mass ratio of approximately 2 mL / 1 g, vortex mix, and obtain a suspension.

[0024] (c) Centrifuge the suspension, take the supernatant, add an equal volume of pure water to obtain a liquid sample.

[0025] For example, the extraction solvent volume can be approximately 0.4 mL, and the soil sample can be approximately 0.2 g. That is, only about 0.2 g of soil and about 0.2 mL of acetonitrile are needed to quantitatively analyze the content of imidacloprid and fipronil and their metabolites in the soil.

[0026] When establishing the standard curves of each compound described in step (2) above, the matrix solvent was prepared by using soil free of pesticide residues as raw material as follows: Weigh 0.2g of freeze-dried soil, add 400μL of extraction solvent (acetonitrile:water = 1:1 v / v, containing 5% formic acid), vortex for 1min, shake for 10min, centrifuge for 10min, take the supernatant, add the same amount of pure water, mix well, centrifuge for 10min, take the supernatant, and obtain the matrix solvent.

[0027] Prepare a blank solvent as follows: use an acetonitrile:water = 1:3 (v / v) solution as the blank solvent.

[0028] Mixed matrix solvent standard solutions (matrix standards) and blank solvent standard solutions (solvent standards) with concentrations of 0.01 ng / mL, 0.05 ng / mL, 0.1 ng / mL, 0.5 ng / mL, 1 ng / mL, 5 ng / mL, 10 ng / mL, 50 ng / mL, 100 ng / mL, 500 ng / mL, and 1000 ng / mL were prepared using the above solvents. These solutions were then analyzed by LC-MS / MS, and peak areas were recorded. Matrix standard curves and blank solvent standard curves were fitted. The matrix effect (ME) of each compound was obtained by dividing the slope of the matrix standard curve by the slope of the blank solvent standard curve.

[0029] Those skilled in the art will readily understand that when the content of a compound exceeds the linear range of the standard curve, the liquid sample can be diluted using gradient dilution or multiple dilution methods before content detection.

[0030] In the above method, the liquid phase conditions can be, for example, as follows: column: Agilent XBD C18 (100mm*3mm, 1.8μm); column temperature: 40℃; injection volume: 1μL.

[0031] The instruments used can be, for example, ExionLC. TM AD+QTRAP 6500plus.

[0032] Accordingly, the mass spectrometry conditions are, for example, CUR: 35 psi; CAD: Medium; IS: 5500 V; TEM: 550 °C; GS1: 50 psi; GA2: 50 psi.

[0033] This invention employs LC-MS / MS to determine imidacloprid and fipronil and their metabolites in soil. The method requires a small sample size, simple pretreatment, and low consumption of organic reagents. It can simultaneously detect 10 compounds, including the two pesticides and their metabolites. This method overcomes the shortcomings of existing technologies, such as large sample size, complex pretreatment, and high consumption of organic reagents, and has significant potential for widespread application. Attached Figure Description

[0034] Figure 1 The XIC plots are shown for LC-MS / MS detection of 10 compounds, including imidacloprid, fipronil, and their metabolites, at a concentration of 50 ng / mL.

[0035] Figure 2 The XIC plots show the content of imidacloprid and fipronil and their metabolites in soil from randomly selected rice experimental fields detected by LC-MS / MS.

[0036] Figure 3 This paper presents a sensitivity comparison for LC-MS / MS detection of imidacloprid and fipronil and their metabolites using a conventional method with a 0.1% formic acid-water-acetonitrile mixed solvent (b) and the present invention using a mobile phase of 2 mM ammonium formate and 0.01% formic acid-water-methanol (a). In graph a, the mobile phases are water and methanol with the addition of 2 mM ammonium formate and 0.01% formic acid, respectively; in graph b, the mobile phases are water and acetonitrile with the addition of 0.1% formic acid, respectively. The signal-to-noise ratio (S / N) of each compound shown in the graphs indicates that the addition of 2 mM ammonium formate and 0.01% formic acid to the mobile phases of water and methanol, respectively, significantly improves the S / N of all compounds, with the highest improvement reaching more than ten times.

[0037] Figure 4 The LC-MS / MS peak shapes of soil extracts before and after dilution with pure water at a 1:1 ratio are shown. The upper graph shows the liquid sample containing acetonitrile:water = 1:1 (v / v), and the lower graph shows the liquid sample containing acetonitrile:water = 1:3 (v / v). Due to the solvent effect, the 1-methyl-3-[(3-tetrahydrofuran)methyl]dihydroguanidine salt DIN-DN compound exhibited a double peak; after dilution with water by 1 / 2, it became a single peak with a good peak shape. Detailed Implementation

[0038] This invention provides a rapid and simple mass spectrometry method for screening the residual content of two pesticides, imidacloprid and fipronil, and their metabolic degradation products in the environment (such as soil), which can provide a reliable basis for environmental assessment.

[0039] Traditional methods require large sample sizes for pretreatment, typically 10g of soil, and use a significant amount of extraction solvent, usually 20mL of organic reagent, along with purification steps. In contrast, the method of this invention requires only 0.2g of soil sample, consuming only 0.4mL of solvent. After simple mixing and centrifugation, quantitative detection of various compounds can be performed with high accuracy.

[0040] In this article, the term "compound component" refers to imidacloprid (IMI) and its metabolites 1-[(6-chloropyridin-3-yl)methyl]-1-nitroguanidine (IMI-NG), imidacloprid-guanidine hydrochloride (IMI-Des), imidacloprid olefin (IMI-Olefin), imidacloprid urea (IMI-Urea), 6-hydroxynicotinic acid (IMI-HNA), and 6-chloronicotinic acid (IMI-CINA); and fipronil (DIN) and its metabolites 1-methyl-3-[(3-tetrahydrofuran)methyl]urea (DIN-UF) and 1-methyl-3-[(3-tetrahydrofuran)methyl]dihydroguanidine salt (DIN-DN).

[0041] In this article, the term "metabolism" refers to the transformation and decomposition of pesticides such as imidacloprid and fipronil by plants or microorganisms, or their degradation by physicochemical factors.

[0042] When detecting the above compounds using conventional methods, the mobile phase in liquid chromatography is typically a 0.1% formic acid-acetonitrile mixture. Through repeated optimization of the mobile phase, this invention discovered that using a combination of salt and acid yields unexpectedly good results. Using an aqueous solution containing approximately 2 mM ammonium formate and approximately 0.01% formic acid as the aqueous phase A, and a methanol solution containing approximately 2 mM ammonium formate and approximately 0.01% formic acid as the organic phase B, LC-MS / MS detection of these compounds significantly increased the sensitivity of the compounds and effectively reduced the mass spectrometry noise of 10 compounds. The addition of 0.01% formic acid further improved the sensitivity of all 10 compounds. The effect of increasing compound sensitivity is particularly pronounced when simultaneously detecting multiple compounds. However, excessively high salt and acid concentrations can lead to decreased sensitivity and increased mass spectrometry noise. Currently, there are no literature reports on the simultaneous detection of imidacloprid and fipronil and their multiple metabolites.

[0043] In this paper, when describing numerical characteristics, the terms "about", "approximately", or "around" refer to the fact that the expressed number may have an error range or fluctuation range of ±10%, ±9%, ±8%, ±7%, ±6%, or ±5%.

[0044] Unless otherwise defined, the range of numerals used in this invention includes the numeral and any number within that range.

[0045] In the method of this invention, a standard curve can be established for these 10 compounds. Using this standard curve, absolute quantification of compounds with reference standards and relative quantification of compounds without reference standards can be performed. Because the invention includes parameters for two fragment ion channels—a quantitative ion channel and a qualitative ion channel—combined with the retention time of the compounds, it is possible to determine whether a compound belongs to the 10 compounds even without reference standards, and relative quantification can be performed due to structural similarity.

[0046] In one embodiment, when this invention is used for soil analysis, the extracted sample requires pretreatment. When preparing liquid samples, an acetonitrile:water ratio of approximately 1:1 (v / v) containing about 5% formic acid is used as the extraction solvent. This avoids the influence of many impurities in the soil on the analysis of the target compounds, as soil contains minerals, organic matter, microorganisms, etc., and these impurities include fat-soluble substances and nitrogen-containing compounds. Therefore, a special organic solvent is needed to separate these impurities from the target pesticide components based on the principle of "like dissolves like." However, in experiments, it is not sufficient to use a solvent that can separate impurities from pesticide components in the soil; it is also necessary to ensure that the extraction rate and types of pesticide components in the soil are not reduced during separation. Through extensive experimental trials, the inventors have provided an acetonitrile:water ratio of approximately 1:1 (v / v) (containing about 5% formic acid) extraction solvent, which meets the requirements of sufficient impurity separation while maintaining pesticide residue levels. This extraction solvent can effectively separate imidacloprid and fipronil and their metabolites, totaling 10 compounds.

[0047] After treating freeze-dried soil with extraction solvent to obtain soil extract samples, pretreatment is required. In pretreatment, the soil extract samples are diluted with pure water at a volume ratio of 1:1 to obtain samples suitable for LC-MS / MS loading. This avoids the solvent effect of highly polar compounds and ensures good peak shape (see...). Figure 4 A good peak shape is essential for data reproducibility and stability. Pretreatment methods can effectively remove interference from soil impurities on imidacloprid, fipronil, and their metabolites. Specifically, the response of the matrix standard is 0.8–1.2 times that of the solvent standard; therefore, the solvent standard can be used for quantification, avoiding the preparation of the matrix standard, simplifying experimental steps, and saving time and costs.

[0048] This invention investigated the linearity, matrix effect, and recovery rate of the above 10 compounds, confirming that the method is simple, rapid, and has good separation effect. The accuracy and precision can meet the requirements of quantitative analysis, and it has the advantages of high sensitivity, good repeatability, simple operation, speed, and accuracy.

[0049] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0050] This article involves the addition amount, content and concentration of various substances. Unless otherwise specified, the percentage content mentioned refers to the volume percentage.

[0051] If the experimental operating temperature is not specifically specified in the examples, the temperature usually refers to room temperature (10-30°C).

[0052] Example 1: Determination of imidacloprid, fipronil and their metabolites in soil

[0053] 1. Sample pretreatment

[0054] Prepare the extraction solvent: acetonitrile:water ≈ 1:1 (v / v), plus 5% formic acid;

[0055] Soil extraction: Weigh 0.2 g of freeze-dried soil, add 400 μL of extraction solvent, vortex for 1 min, shake for 10 min, centrifuge for 10 min, and collect 100 μL of supernatant to obtain the soil extraction sample. Add 100 μL of pure water, mix well, centrifuge for 10 min, collect the supernatant to obtain the liquid sample for loading, and perform LC-MS / MS detection.

[0056] 2. LC-MS / MS detection

[0057] Instrument: ExionLC TM AD+QTRAP 6500 plus

[0058] Liquid phase method

[0059] Column: Agilent XBD C18 (100mm*3mm, 1.8μm);

[0060] Column temperature: 40℃;

[0061] Injection volume: 1 μL;

[0062] Aqueous phase A: An aqueous solution containing 2 mM ammonium formate and 0.01% formic acid;

[0063] Organic phase B: A methanol solution containing 2 mM ammonium formate and 0.01% formic acid;

[0064] Gradient elution is shown in Table 1

[0065] Table 1 Gradient elution parameters

[0066]

[0067] Mass spectrometry

[0068] CUR: 35psi;

[0069] CAD: Medium;

[0070] IS: 5500V;

[0071] TEM: 550℃;

[0072] GS1: 50psi;

[0073] GA2: 50 psi;

[0074] Other parameters are shown in Table 2.

[0075] Table 2 Mass Spectrometry Detection Parameters

[0076]

[0077] Note*: Two fragment ion channels are selected for each compound: 1 is the quantitative ion channel, and 2 is the qualitative ion channel.

[0078] 3. Determine linear correlation

[0079] Mixed solutions of 0.01 ng / mL, 0.05 ng / mL, 0.1 ng / mL, 0.5 ng / mL, 1 ng / mL, 5 ng / mL, 10 ng / mL, 50 ng / mL, 100 ng / mL, 500 ng / mL, and 1000 ng / mL were prepared using acetonitrile:water at a ratio of 1:3 (v / v), and then analyzed by LC-MS / MS. The linear range and correlation coefficients are shown in Table 3.

[0080] Table 3 Linear Range

[0081]

[0082] 4. Prepare a mixed solution of 10 compounds, including imidacloprid, fipronil, and their metabolites, at a concentration of 50 ng / mL. The XIC chromatograms obtained by LC-MS / MS detection are shown below. Figure 1 As shown.

[0083] Figure 2 The XIC plots show the concentrations of imidacloprid and fipronil and their metabolites in the soil of randomly selected rice experimental fields as determined by LC-MS / MS.

[0084] 5. Prepare a 50 ng / mL solution of imidacloprid. Use water and acetonitrile containing 0.1% formic acid as mobile phases, as used in conventional methods, for LC-MS / MS detection. Then, use solutions of water and methanol containing 2 mM ammonium formate and 0.01% formic acid as mobile phases for LC-MS / MS detection. The XIC chromatograms for both are shown below. Figure 3 As shown in the figure. The comparative results show that the sensitivity of the present invention is significantly better than that of the traditional method when using solutions of water and methanol containing 2 mM ammonium formate and 0.01% formic acid, respectively, as the mobile phase.

[0085] Example 2: Detection of matrix effect

[0086] Using soil free of pesticide residues as raw material, the matrix solvent was prepared as follows: Weigh 0.2g of freeze-dried soil, add 400μL of extraction solvent (acetonitrile:water = 1:1 v / v, containing about 5% formic acid), vortex for 1min, shake for 10min, centrifuge for 10min, take the supernatant, add the same amount of pure water, mix well, centrifuge for 10min, take the supernatant, and obtain the matrix solvent.

[0087] Prepare a blank solvent as follows: use an acetonitrile:water = 1:3 (v / v) solution as the blank solvent.

[0088] Matrix and solvent standards with concentrations of 0.01 ng / mL, 0.05 ng / mL, 0.1 ng / mL, 0.5 ng / mL, 1 ng / mL, 5 ng / mL, 10 ng / mL, 50 ng / mL, 100 ng / mL, 500 ng / mL, and 1000 ng / mL were prepared using the solvents described above. These standards were then analyzed by LC-MS / MS, and the peak areas were recorded. Matrix and solvent standard curves were fitted, and the matrix effect (ME) was obtained by dividing the slope of the matrix standard curve by the slope of the solvent standard curve. The results are shown in Table 4.

[0089] Table 4. Investigation of matrix effect

[0090] Compound Name ME IMI 1.11 IMI-NG 1.08 IMI-Des 0.965 IMI-Olefin 0.835 IMI-Urea 1.19 IMI-HNA 1.05 IMI-CINA 1.06 DIN 1.05 DIN-UF 1.01 DIN-DN 0.920

[0091] Table 4 shows that matrix effect (ME) values ​​between 0.8 and 1.2 are considered to have no matrix effect. A ME greater than 1.2 is considered a matrix-enhancing effect. A ME less than 0.8 is considered a matrix-inhibiting effect. Table 4 also shows that the matrix effect of all compounds in soil ranges from 0.8 to 1.2. This indicates that the concentration in the sample can be calculated using solvent standards.

[0092] Precision and accuracy

[0093] The recoveries of 10 target compounds were determined at two different spiking concentrations (5 ng / g and 50 ng / g), with each concentration repeated five times. See Table 5 for details.

[0094] Table 5. Soil addition and recovery results (5 replicates)

[0095]

[0096]

[0097] Table 5 shows that, with spiking at the 5 ng / g level, the average recovery rate was 75.8%–119%, with a relative standard deviation of 4.7%–11.4%; with spiking at the 50 ng / g level, the average recovery rate was 89.6%–112%, with a relative standard deviation of 1.4%–8.2%. This indicates that the LC-MS / MS detection method of the present invention has high precision and accuracy.

[0098] The above embodiments are provided to facilitate understanding and use of the present invention by those skilled in the art, but the present invention is not limited to the above embodiments. Any improvements and modifications made by those skilled in the art based on the principles of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for simultaneously determining imidacloprid, fipronil, and their metabolites in soil, characterized in that, Includes the following steps: (1) Liquid samples containing imidacloprid and fipronil and their metabolites were detected by liquid chromatography-tandem triple quadrupole mass spectrometry (LC-MS / MS); The mobile phases used in the liquid chromatography were: aqueous phase A: an aqueous solution containing 0.5–4 mM ammonium formate and 0.005–0.02% formic acid; organic phase B: a methanol solution containing 0.5–4 mM ammonium formate and 0.005–0.02% formic acid; and an Agilent XBD C18 column, 100 mm * 3 mm, 1.8 µm. In mass spectrometry detection, two ion channels are selected for each compound: one quantitative ion channel and one qualitative ion channel. For imidacloprid, the quantitative and qualitative ion channels are respectively... m / z 256>209 and m / z 256>175; the quantitative and qualitative ion channels for fipronil are respectively m / z 203>113 and m / z 203 > 157; (2) The content of each compound was determined according to the standard curve of each compound. The metabolites of imidacloprid were selected from the following compounds: 1-[(6-chloropyridin-3-yl)methyl]-1-nitroguanidine, imidacloprid-guanidine hydrochloride, imidacloprid olefin, imidacloprid urea, 6-hydroxynicotinic acid, and 6-chloronicotinic acid; the metabolites of flufenoxuron were selected from the following compounds: 1-methyl-3-[(3-tetrahydrofuran)methyl]urea, 1-methyl-3-[(3-tetrahydrofuran)methyl]dihydroguanidine salt. The liquid sample was obtained from soil, and the extraction of the liquid sample included the following steps: (a) Prepare a mixed solvent of acetonitrile:water (v / v) = 1:0.5-1.5, and add 3-8% formic acid to obtain the extraction solvent; (b) Add the extraction solvent obtained in step (a) to the freeze-dried soil at a volume / mass ratio of approximately 2 mL / 1 g, vortex mix, and obtain a suspension; (c) Centrifuge the suspension, take the supernatant, add an equal volume of pure water to obtain a liquid sample.

2. The method as described in claim 1, characterized in that, In step (1), the aqueous phase A is an aqueous solution containing 2 mM ammonium formate and 0.01% formic acid; the organic phase B is a methanol solution containing 2 mM ammonium formate and 0.01% formic acid.

3. The method as described in claim 1, characterized in that: The quantitative and qualitative ion channels of 1-[(6-chloropyridin-3-yl)methyl]-1-nitroguanidine are respectively m / z 230>186 and m / z 230 > 148; The quantitative and qualitative ion channels of imidacloprid-guanidine hydrochloride are respectively m / z 211>126 and m / z 211>90; The quantitative and qualitative ion channels of imidacloprid are respectively m / z 254>205 and m / z 254>171; The quantitative and qualitative ion channels of imidacloprid are respectively m / z 212>128 and m / z 212>99; The quantitative and qualitative ion channels of 6-hydroxynicotinic acid are respectively m / z 140>122 and m / z 140 > 78; The quantitative and qualitative ion channels of 6-chloronicotinic acid are respectively m / z 158>122 and m / z 160 > 122; The quantitative and qualitative ion channels of 1-methyl-3-[(3-tetrahydrofuran)methyl]urea are respectively m / z 159>102 and m / z 159>67; The quantitative and qualitative ion channels of 1-methyl-3-[(3-tetrahydrofuran)methyl]dihydroguanidine salt are respectively m / z 158>102 and m / z 158>57.

4. The method as described in claim 1, characterized in that, The extraction solvent volume was 0.4 mL, and the soil sample was 0.2 g.

5. The method as described in claim 1, characterized in that, When establishing the standard curves of each compound described in step (2), the matrix solvent was prepared using soil free of pesticide residues as raw material as follows: Weigh 0.2 g of freeze-dried soil, add 400 mL of extraction solvent, vortex for 1 min, shake for 10 min, centrifuge for 10 min, take the supernatant, add the same amount of pure water, mix well, centrifuge for 10 min, take the supernatant, and obtain the matrix solvent, wherein the extraction solvent is: acetonitrile:water = 1:1 v / v, containing 5% formic acid.

6. The method as described in claim 1, characterized in that, When establishing standard curves for each compound, the concentration range of each compound was from 0.01 ng / mL to 1000 ng / mL.

7. The method as described in claim 6, characterized in that, The blank solvent is an acetonitrile:water solution with a ratio of 1:3 (v / v).

8. The method as described in claim 7, characterized in that, Mixed matrix solvent standard solutions (matrix standards) and blank solvent standard solutions (solvent standards) were prepared using solvents to prepare standard solutions of various compounds at concentrations of 0.01 ng / mL, 0.05 ng / mL, 0.1 ng / mL, 0.5 ng / mL, 1 ng / mL, 5 ng / mL, 10 ng / mL, 50 ng / mL, 100 ng / mL, 500 ng / mL, and 1000 ng / mL. These solutions were then analyzed by LC-MS / MS, and the peak areas were recorded. A matrix standard curve and a blank solvent standard curve were fitted. The matrix effect of each compound was obtained by dividing the slope of the matrix standard curve by the slope of the blank solvent standard curve.

9. The method as described in claim 1, characterized in that, The liquid chromatography conditions were: column temperature: 40℃; injection volume: 1 mL.

10. The method as described in claim 9, characterized in that, The mass spectrometry conditions were as follows: CUR: 35 psi; CAD: Medium; IS: 5500 V; TEM: 550℃; GS1: 50 psi; GA2: 50 psi.

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