Method for measuring pesticide residue in tea leaves

Abstract

The invention relates to the technical field of pesticide detection, in particular to a method for measuring pesticide residues in tea, which comprises the steps of sample pretreatment, sample purification, matrix calibration and correction of detection results based on a calibration curve. According to the method, by optimizing the steps of sample pretreatment, purification and detection, the matrix effect of the tea leaves can be effectively reduced, and the accuracy and reliability of determination of the pesticide residues in the tea leaves are improved. Meanwhile, the problem that glyphosate and glufosinate-ammonium cannot be combined with other pesticides for inspection is solved, the pesticide detection accuracy is guaranteed, and meanwhile the pesticide detection convenience is improved. The method disclosed by the invention is reasonable in operation flow, can be used for rapidly and accurately measuring the pesticide residue in the tea leaves, and provides powerful technical support for quality safety supervision and quality control of the tea leaves and health guarantee of consumers.

Description

Technical Field

[0001] The present invention relates to the technical field of pesticide detection, and particularly relates to a method for determining the pesticide residue content in tea. Background Art

[0002] With the continuous development of agricultural production, the use of pesticides has played an important role in improving the yield and quality of crops. However, the problem of pesticide residues has also attracted increasing attention. Especially for tea, a widely consumed agricultural product in people's daily lives, the accurate determination of its pesticide residue content is crucial for ensuring food safety and consumer health.

[0003] As a complex biological matrix, the components in tea may interfere with the detection of pesticides, resulting in deviation of detection results. It is difficult to effectively purify the matrix in tea during the extraction and purification stages for existing tea, resulting in a large amount of tea matrix content having a greater impact on the determination. In addition, existing detection technologies are difficult to combine the detection of glyphosate and glufosinate with other pesticides, resulting in complex and cumbersome steps for the determination of pesticide residues.

[0004] Therefore, a more efficient, accurate and reliable determination method is needed to solve these problems. Summary of the Invention

[0005] The present invention aims to provide a method for determining the pesticide residue content in tea, and improve the accuracy and reliability of the determination of pesticide residue content in tea.

[0006] To solve the above technical problems, the technical solutions provided by the present invention are as follows: A method for determining the pesticide residue content in tea, comprising the following steps: S1. Sample pretreatment: Grind the tea into powder, extract it successively with water and acetonitrile, and obtain extract A and extract B respectively; S2. Sample purification: Purify extract A with dichloromethane, purify extract B with PSA powder, obtain purified solution A and purified solution B respectively, combine the above two purified solutions, mix well, add C18 powder and GCB powder for centrifugation, take the supernatant, and dry it by blowing nitrogen; S3. Detect the sample using liquid chromatography-tandem mass spectrometry: Dissolve the dried residue obtained in step S2 with a mixed solution of acetonitrile and water, filter it through a microporous filter membrane, perform liquid chromatography separation with a C18 chromatographic column, gradient elution, and then detect it with a mass spectrometer; S4. Matrix calibration: Prepare the matrix extraction solution of blank sample tea leaves and the standard solution for detecting pesticides respectively, and then mix the two evenly to prepare matrix calibration solutions with different concentrations. Perform liquid chromatography-tandem mass spectrometry detection on the matrix calibration solutions respectively, and draw the standard curve after matrix calibration; S5. Correct the detection results based on the calibration curve: Put the characteristic ion peak areas of each pesticide in the tea leaf sample detected in step S3 into the corresponding pesticide standard curve to obtain the accurate concentration values of each pesticide in the sample.

[0007] As an improvement, the specific steps of the sample pretreatment in step S1 are as follows: Grind the tea leaves into powder, then weigh 2 g of the tea leaf powder, add 15 mL of deionized water, perform ultrasonic extraction for 30 min under the condition of a 45 °C water bath, and filter by suction to obtain the extraction solution, denoted as extraction solution A; Put the filter residue after suction filtration into a centrifuge tube, add 15 mL of acetonitrile, and perform ultrasonic extraction for 30 min; add 4 g of sodium chloride, 3 g of anhydrous magnesium sulfate, and 1 g of anhydrous sodium acetate, mix evenly, and centrifuge at 8000 - 10000 r / min for 5 - 10 min; take the supernatant, repeat the extraction of the residue with 15 mL of acetonitrile once, combine the two extraction solutions, and then concentrate by nitrogen blowing to 5 mL, denoted as extraction solution B.

[0008] As an improvement, the specific steps of the sample pretreatment in step S2 are as follows: S2-1. Purification of extraction solution A: Add 20 mL of dichloromethane to the centrifuge tube of extraction solution A, place it on a vortex oscillator for high-speed vortex mixing, with the mixing time being 30 - 60 s, and then place it in a centrifuge and centrifuge at a speed of 8000 - 10000 r / min for 3 - 5 min. Take the upper aqueous phase, denoted as purified solution A; S2-2. Purification of extraction solution B: Add 60 - 80 mg of PSA powder to extraction solution B, mix well, and centrifuge at 8000 - 10000 r / min for 3 - 5 min. This step can be centrifuged synchronously with the purification step of extraction solution A. After centrifugation, take the upper clear liquid and denote it as purified solution B; S2-3. Combined purification: Combine purified solution A and purified solution B, then add 30 - 80 mg of C18 powder and GCB powder each, mix well, and centrifuge at 10000 r / min in a centrifuge for 5 min. Take the upper clear liquid and dry it by nitrogen blowing.

[0009] As an improvement, in the acetonitrile-water mixed solution in step S3, the volume fractions of acetonitrile and water are 40% and 60% respectively.

[0010] As an improvement, the column temperature of the chromatographic column in step S3 is 40 °C, the injection volume is 10 μL, and the flow rate is 0.3 mL / min; gradient elution is performed, and the mobile phase consists of mobile phase A and mobile phase B; wherein, mobile phase A is an aqueous solution of 0.1% formic acid and 4 mmol / L ammonium acetate, and mobile phase B is acetonitrile.

[0011] As an improvement in the process, the gradient elution sequence is as follows: 0 min: 95% mobile phase A, 5% mobile phase B; 3 min: 80% mobile phase A, 20% mobile phase B; 6 min: 65% mobile phase A, 35% mobile phase B; 9 min: 50% mobile phase A, 50% mobile phase B; 12 min: 95% mobile phase A, 5% mobile phase B.

[0012] As an improvement, the mass spectrometry conditions in step S3 are as follows: Ion source: electrospray ionization source (ESI); Scanning mode: positive and negative ion switching scanning mode; Detection mode: multiple reaction monitoring (MRM) mode; Spray voltage: positive ion spray voltage: 2500 V, negative ion spray voltage: -2000 V; Atomization temperature: 290 - 300 °C, ion transfer tube temperature: 285 °C, sheath gas flow rate: 60 arb, auxiliary gas flow rate: 15 arb.

[0013] As an improvement, the method for matrix calibration in step S4 is as follows: First, prepare the matrix extraction solution. Weigh 10.0 g of tea sample into a 50 mL centrifuge tube, add 20 mL of acetonitrile, vortex for 2 min to fully mix the tea and acetonitrile, then add 10 mL of ultrapure water and vortex again for 1 min to ensure full mixing of water and acetonitrile. Place the centrifuge tube in an ice bath and ultrasonically extract for 15 min, then centrifuge at 4000 rpm for 10 min to precipitate the tea residue and solid impurities, obtaining the matrix extraction solution; Weigh the pesticide standard to be detected. Transfer 1 mL of each pesticide standard to a 50 mL volumetric flask respectively, dilute to the mark with ethyl acetate to prepare a mixed standard solution of 2 mg / L. Take the mixed standard solution and prepare a series of mixed standard solutions with mass concentrations of 1 μg / L, 10 μg / L, 50 μg / L, 100 μg / L, and 200 μg / L step by step with ethyl acetate; Mix the standard solution and the matrix extraction solution evenly in proportion to prepare matrix calibration solutions with different concentrations. Perform liquid chromatography - tandem mass spectrometry detection on the matrix calibration solutions respectively, record the characteristic ion peak areas of each pesticide standard, and plot the standard curve after matrix calibration.

[0014] As an improvement, the pesticides to be detected include: glyphosate, glufosinate, methomyl, carbendazim, thiamethoxam, imidacloprid, carbofuran, carbaryl, acetamiprid, diflubenzuron, phoxim, indoxacarb.

[0015] The advantages of the present invention are as follows: 1. By optimizing the sample pretreatment steps, the present invention uses water and acetonitrile to extract pesticide residues in tea leaves respectively, which can extract pesticides with different properties more comprehensively and improve the extraction efficiency. In the treatment of extract A, ultrasonic extraction in a water bath at 45°C is used, combined with subsequent suction filtration operation, which can effectively separate water-soluble pesticide components; while extract B is extracted by acetonitrile, and salts such as sodium chloride, anhydrous magnesium sulfate and anhydrous sodium acetate are added. Using the salting-out effect and centrifugation operation, pesticides with slightly weaker or non-polar properties can be effectively extracted. The present invention overcomes the problem that glyphosate and glufosinate cannot be jointly tested with other pesticides, and improves the convenience of pesticide detection while ensuring the accuracy of pesticide detection.

[0016] 2. In the sample purification step of the present invention, the extract A containing glyphosate and glufosinate and the extract B containing other pesticides are purified separately, which can effectively remove the tea matrix in the extract. After purification, the two are combined and purified by C18 and GCB powders. C18 and GCB powders can effectively purify non-polar pesticides and tea substrates such as pigments. The combination can effectively remove matrixes such as tea polyphenols in the original extract A, avoiding interference of the tea matrix on pesticide determination.

[0017] 3. The detection method uses liquid chromatography - tandem mass spectrometry, which has high sensitivity and high specificity. At the same time, since the detection items contain both strongly polar and weakly polar pesticides, the present invention specifically configures the proportion of the acetonitrile-water mixed solution, so that various pesticides can be repeatedly dissolved in the mixed solution.

[0018] 4. The present invention introduces a matrix calibration step, which can effectively reduce the matrix effect of tea leaves. By preparing the matrix extract of blank sample tea leaves and the standard solution of the pesticides to be detected, and mixing the two to prepare matrix calibration solutions with different concentrations, simulating the matrix environment in the actual sample, the influence of the matrix on the detection signal is fully considered when drawing the standard curve. The standard curve after matrix calibration can more truly reflect the relationship between the pesticide concentration and the detection signal in the sample. Therefore, when correcting the detection results, more accurate pesticide concentration values can be obtained, improving the reliability of the detection results.

[0019] 5. The operation process of the method of the present invention is reasonable, the connection between each step is tight, and it is easy to be popularized and applied in actual detection work. From the grinding, extraction, purification of samples to detection and result analysis, the whole process is standardized and efficient. It can realize the rapid and accurate determination of pesticide residues in tea under the premise of ensuring the detection quality, and provides strong technical support for the supervision of tea quality and safety, quality control and consumer health protection. Detailed implementation manners

[0020] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated here can be arranged and designed in various different configurations.

[0021] A method for determining the pesticide residue content in tea, comprising the following steps: S1. Sample pretreatment: Grind the tea into powder, then weigh 2 g of the tea powder, accurate to 0.001 g, add it into a centrifuge tube, then add 15 mL of deionized water, and ultrasonically extract for 30 min under the condition of a 45°C water bath. Filter by suction to obtain the extract, denoted as extract A.

[0022] Extract A is extracted with deionized water, mainly used for extracting pesticides with large polarity, which are easily soluble in water and hardly soluble in organic solvents, such as: glyphosate or glufosinate.

[0023] Add the filter residue obtained by suction filtration into a centrifuge tube, add 15 mL of acetonitrile, and ultrasonically extract for 30 min; add 4 g of sodium chloride, 3 g of anhydrous magnesium sulfate, and 1 g of anhydrous sodium acetate, mix evenly, and centrifuge at 8000 - 10000 r / min for 5 - 10 min; take the supernatant, repeat the extraction of the residue with 15 mL of acetonitrile once, combine the two extracts, and then concentrate to 5 mL by nitrogen blowing, denoted as extract B.

[0024] The filter residue is ultrasonically extracted with acetonitrile, which can extract carbamate pesticides in the filter residue, such as: carbofuran, methomyl, etc., and organophosphorus pesticides with slightly weaker polarity.

[0025] S2. Sample purification: Purify extract A and extract B respectively.

[0026] Add 20 mL of dichloromethane to the centrifuge tube of extract A, place it on a vortex oscillator for high-speed vortex mixing, the mixing time is 30-60 seconds, so that dichloromethane and extract A are fully contacted and mixed, promote the dissolution of glyphosate and the full extraction of impurities, and then place it on a centrifuge at a speed of 8000-10000 r / min for 3-5 minutes. After centrifugation, the mixed solution is divided into upper and lower layers, the upper layer is an aqueous solution containing glyphosate, and the lower layer is a dichloromethane phase. Take the upper aqueous phase and record it as purified solution A.

[0027] Since the extract A is extracted with deionized water, it contains more impurities. The caffeine, alkaloids and other components in the extract A can be removed by dichloromethane shaking extraction, thereby reducing the interference of the corresponding impurities on subsequent detection.

[0028] The purification method of extract B is as follows: add 60-80 mg of PSA powder to extract B, mix thoroughly, and centrifuge at 8000-10000 r / min for 3-5 minutes. This step can be centrifuged synchronously with the purification step of extract A. After centrifugation, take the supernatant and record it as purified liquid B. PSA (N-propylethylenediamine) is suitable for the adsorption of polar compounds and can effectively reduce polar impurities in extract B.

[0029] Combine Purification Solution A and Purification Solution B, then add C 18 30-80 mg of each of the powder and GCB powder were mixed thoroughly, and then centrifuged at 10,000 r / min for 5 min. The supernatant was taken and dried by nitrogen blowing.

[0030] S3. Detection of samples using liquid chromatography-tandem mass spectrometry: The dried residue obtained in step S2 was dissolved in 3 mL of a mixed solution of acetonitrile and water, and filtered through a microporous membrane. 18 The chromatographic column was used for liquid chromatography separation. The volume fractions of acetonitrile and water in the acetonitrile-water mixed solution were 40% and 60%, respectively, and the pore size during microfiltration was 0.2 μm.

[0031] During chromatographic column separation, the column temperature was 40°C, the injection volume was 10 μL, and the flow rate was 0.3 mL / min; gradient elution was performed. The mobile phase consisted of mobile phase A and mobile phase B; mobile phase A was an aqueous solution of 0.1% formic acid and 4 mmol / L ammonium acetate, and mobile phase B was acetonitrile.

[0032] The gradient elution program is as follows: 0 min: mobile phase A 95%, mobile phase B 5%; 3 min: mobile phase A 80%, mobile phase B 20%; 6 min: mobile phase A 65%, mobile phase B 35%; 9 min: mobile phase A 50%, mobile phase B 50%; 12 min: mobile phase A 95%, mobile phase B 5%.

[0033] The mass spectrometry conditions are as follows: Ion source: electrospray ionization source (ESI).

[0034] Scanning mode: positive and negative ion switching scanning mode.

[0035] Detection mode: multiple reaction monitoring (MRM) mode.

[0036] Spray voltage: positive ion spray voltage: 2500 V, negative ion spray voltage: -2000 V.

[0037] Atomization temperature: 290 - 300 °C. Ion transfer tube temperature: 285 °C. Sheath gas flow rate: 60 arb, auxiliary gas flow rate: 15 arb.

[0038] S4. Matrix calibration: First, prepare the matrix extraction solution. Weigh 10.0 g of tea sample into a 50 mL centrifuge tube, add 20 mL of acetonitrile, and vortex for 2 min to fully mix the tea and acetonitrile. Then add 10 mL of ultrapure water and vortex again for 1 min to ensure full mixing of water and acetonitrile, forming a suitable extraction system. Place the centrifuge tube in an ice bath and ultrasonically extract for 15 min to fully release the pesticide components in the tea into the extraction solution. Then centrifuge at 4000 rpm for 10 min to precipitate the tea residue and solid impurities, obtaining the matrix extraction solution.

[0039] Weigh 12 pesticide standards. Transfer 1 mL of each of the 12 pesticide standards (100 mg / L) into a 50 mL volumetric flask respectively, and make up to the mark with ethyl acetate to prepare a mixed standard solution of 2 mg / L. Take an appropriate amount of the mixed standard solution and use ethyl acetate to gradually prepare a series of mixed standard solutions with mass concentrations of 10 μg / L, 50 μg / L, and 100 μg / L respectively.

[0040] Mix the standard solution and the matrix extract evenly in proportion to prepare matrix calibration solutions with different concentrations. Perform liquid chromatography-tandem mass spectrometry detection on the matrix calibration solutions respectively, and record the characteristic ion peak areas of each pesticide standard. Take the mass concentration (μg / L) of each pesticide in the matrix calibration solution as the abscissa (X), and the corresponding characteristic ion peak area or peak height as the ordinate (Y), and draw the standard curves of 12 pesticides after matrix calibration respectively. It is required that the correlation coefficient (R²) of each standard curve should be greater than 0.98 to ensure the accuracy and reliability of the standard curve.

[0041] S5. Correct the detection results based on the calibration curve: Substitute the characteristic ion peak areas of each pesticide in the tea sample detected in step S3 into the standard curve of the corresponding pesticide to obtain the accurate concentration values of each pesticide in the sample. The calculation formula is as follows:

[0042] In the formula, x is the calibrated concentration of the pesticide, with the unit of μg / kg; C is the concentration value corresponding to the detected peak area or peak height obtained from the standard curve, unit: μg / L; D is the dilution factor of the sample during pretreatment and detection; m is the mass of the weighed tea sample, unit: g.

[0043] Example 1

[0044] S1. Sample pretreatment: Take green tea as the test research object, grind the green tea into powder, weigh 2 g of tea powder, add it to a centrifuge tube, add 15 mL of deionized water, and ultrasonically extract for 30 min under the condition of a 45°C water bath, and filter to obtain extract A.

[0045] Add the filter residue to a centrifuge tube, add 15 mL of acetonitrile, and ultrasonically extract for 30 min; add 4 g of sodium chloride, 3 g of anhydrous magnesium sulfate, and 1 g of anhydrous sodium acetate, mix evenly, and centrifuge at 10000 r / min for 5 min; take the supernatant, repeat the extraction of the residue with 15 mL of acetonitrile once, combine the two extraction solutions, and perform a water bath at 45°C and blow nitrogen to concentrate to 5 mL to obtain extract B.

[0046] S2. Sample purification: Add 20 mL of dichloromethane to extract A, place it on a vortex oscillator and vortex mix for 60 s, then centrifuge at a speed of 10000 r / min for 3 min, and take the upper aqueous phase as purification liquid A.

[0047] Add 80 mg of PSA powder to the extraction solution B. After thorough mixing, centrifuge at 10,000 r / min for 3 min, and take the supernatant as the purification solution B. Combine the purification solution A and the purification solution B, add 80 mg each of C18 powder and GCB powder, mix well, centrifuge at 10,000 r / min for 5 min, take the supernatant, and dry it by blowing nitrogen.

[0048] S3. Detect the sample using liquid chromatography - tandem mass spectrometry: Dissolve the dried residue with 3 mL of a mixed solution of acetonitrile - water (the volume fractions of acetonitrile and water are 40% and 60% respectively). After filtering through a 0.2 - μm microporous filter membrane, perform liquid chromatography separation using a C18 chromatographic column. The chromatographic conditions are: column temperature 40°C, injection volume 10 μL, flow rate 0.3 mL / min, and the gradient elution program is the same as above. The mass spectrometry conditions are the same as above.

[0049] S4. Matrix calibration: Detect 12 kinds of pesticide residues in green tea, and the mass spectrometry parameters are shown in Table 1. Prepare the matrix extraction solution and the mixed standard solution of pesticides respectively, and mix the two evenly in proportion to prepare matrix calibration solutions with different concentrations. After performing liquid chromatography - tandem mass spectrometry detection, draw the standard curve after matrix calibration.

[0050] Table 1 Mass spectrometry parameters of pesticides in tea

[0051] S5. Calibration and correction of the detection results: Substitute the characteristic ion peak areas or peak heights of each pesticide in the tea sample detected in step S3 into the standard curve of the corresponding pesticide to obtain the accurate concentration values of each pesticide in the sample. The calculation formula is as follows:

[0052] In the formula, x is the calibrated concentration of the pesticide, with the unit of μg / kg; C is the concentration value corresponding to the detected peak area or peak height obtained from the standard curve, unit: μg / L; D is the dilution factor of the sample during the pretreatment and detection process; m is the mass of the weighed tea sample, unit: g.

[0053] After the correction is completed, calculate the recovery rate and repeat it 6 times. The recovery rate and detection limit are given in Table 2.

[0054] Table 2 Recovery rates and detection limits of 12 kinds of pesticides

[0055] The above data indicate that the recovery rates of this detection method for the 12 kinds of pesticide residues in green tea are between 75% - 95% at different concentrations, and the relative standard deviations are between 3.4% - 7.7%, meeting the verification requirements of pesticide residue detection methods, which proves that this scheme is effective.

[0056] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered by the protection scope of the present invention.

Claims

1. A method for determining pesticide residues in tea, characterized in that: The steps include: S1. Sample pretreatment: Grind the tea leaves and extract them with water and acetonitrile in turn to obtain extract A and extract B respectively; S2. Sample purification: The extract A is purified by using dichloromethane, and the extract B is purified by using PSA powder to obtain purified liquid A and purified liquid B respectively. The purified liquid A and purified liquid B are combined, fully mixed, and then C18 powder and GCB powder are added for centrifugal treatment. The supernatant is taken and dried by blowing nitrogen; S3. Detection of samples using liquid chromatography-tandem mass spectrometry: The dried residue obtained in step S2 is dissolved in a mixed solution of acetonitrile and water, filtered through a microporous filter membrane, separated by liquid chromatography using a C18 chromatographic column, gradient eluted, and then detected by a mass spectrometer; S4. Matrix calibration: Prepare a matrix extract of blank sample tea leaves and a standard solution for detecting pesticides respectively, then mix the two evenly to prepare matrix calibration solutions of different concentrations, perform liquid chromatography-tandem mass spectrometry detection on the matrix calibration solutions respectively, and draw a standard curve after matrix calibration; S5. Correct the test results based on the calibration curve: The characteristic ion peak area of ​​each pesticide in the tea sample detected in step S3 is compared with the standard curve of the corresponding pesticide to obtain the accurate concentration value of each pesticide in the sample.

2. The method for determining the pesticide residue in tea according to claim 1, characterized in that: The specific steps of sample pretreatment in step S1 are: Grind the tea leaves into powder, then weigh 2 g of tea powder, add 15 mL of deionized water, and perform ultrasonic extraction for 30 min in a water bath at 45°C. Filter and obtain the extract, which is recorded as extract A. The filtered residue was added into a centrifuge tube, and 15 mL of acetonitrile was added, and ultrasonic extraction was performed for 30 min; 4 g of sodium chloride, 3 g of anhydrous magnesium sulfate, and 1 g of anhydrous sodium acetate were added, mixed evenly, and centrifuged at 8000-10000 r / min for 5-10 min; the supernatant was taken, and the residue was repeatedly extracted once with 15 mL of acetonitrile, the two extracts were combined, and then concentrated to 5 mL by nitrogen blowing, which was recorded as extract B.

3. The method for determining the pesticide residue in tea according to claim 1, characterized in that: The specific steps of sample pretreatment in step S2 are: S2-1. Purification of extract A: Add 20 mL of dichloromethane to the centrifuge tube of extract A, place on a vortex oscillator for high-speed vortex mixing, the mixing time is 30-60 seconds, and then place on a centrifuge at a speed of 8000-10000 r / min for 3-5 minutes, take the upper aqueous phase, and record it as purified solution A; S2-2. Purification of extract B: Add 60-80 mg of PSA powder to the extract B, mix thoroughly, and centrifuge at 8000-10000 r / min for 3-5 min. After centrifugation, take the supernatant and record it as purified solution B; S2-3. Combined purification: Combine the purified liquid A and the purified liquid B, then add 30-80 mg of C18 powder and GCB powder respectively, mix thoroughly, centrifuge at 10000 r / min for 5 min, take the supernatant, and dry it with nitrogen.

4. The method for determining the pesticide residue in tea according to claim 1, characterized in that: In step S3, the volume fractions of acetonitrile and water in the acetonitrile-water mixed solution are 40% and 60%, respectively.

5. The method for determining the pesticide residue in tea according to claim 1, characterized in that: The column temperature of the chromatographic column in step S3 is 40°C, the injection volume is 10 μL, and the flow rate is 0.3 mL / min; gradient elution is performed, and the mobile phase consists of mobile phase A and mobile phase B; wherein mobile phase A is an aqueous solution of 0.1% formic acid and 4 mmol / L ammonium acetate, and mobile phase B is acetonitrile.

6. The method for determining the pesticide residue in tea according to claim 5, characterized in that: The gradient elution program is: 0 min: mobile phase A 95%, mobile phase B 5%; 3 min: mobile phase A 80%, mobile phase B 20%; 6 min: mobile phase A 65%, mobile phase B 35%; 9 min: mobile phase A 50%, mobile phase B 50%; 12 min: Mobile phase A 95%, mobile phase B 5%.

7. The method for determining the pesticide residue in tea according to claim 1, characterized in that: The mass spectrometry conditions of the liquid chromatography-tandem mass spectrometry in step S3 are: Ion source: electrospray ionization (ESI); Scanning mode: positive and negative ion switching scanning mode; Detection mode: multiple reaction monitoring (MRM) mode; Spray voltage: positive ion spray voltage: 2500V, negative ion spray voltage: -2000V; Atomization temperature: 290-300°C, ion transfer tube temperature: 285°C, sheath gas flow: 60 arb, auxiliary gas flow: 15 arb.

8. The method for determining the pesticide residue in tea according to claim 1, characterized in that: The matrix calibration method in step S4 is: First, prepare the matrix extract solution. Weigh 10.0 g of tea sample into a 50 mL centrifuge tube, add 20 mL of acetonitrile, vortex and oscillate for 2 minutes to fully mix the tea and acetonitrile, then add 10 mL of ultrapure water, vortex and oscillate again for 1 minute to ensure that the water and acetonitrile are fully mixed, place the centrifuge tube in an ice bath for ultrasonic extraction for 15 minutes, and then centrifuge at 4000 rpm for 10 minutes to precipitate the tea residue and solid impurities to obtain the matrix extract solution. Weigh the pesticide standard to be tested, transfer 1 mL of each pesticide standard into a 50 mL volumetric flask, dilute to the mark with ethyl acetate to prepare a 2 mg / L mixed standard solution, and use ethyl acetate to prepare a series of mixed standard solutions with mass concentrations of 10 μg / L, 50 μg / L, and 100 μg / L respectively; The standard solution and matrix extract were mixed evenly in proportion to prepare matrix calibration solutions of different concentrations. The matrix calibration solutions were subjected to liquid chromatography-tandem mass spectrometry detection, the characteristic ion peak area of ​​each pesticide standard was recorded, and the standard curve after matrix calibration was drawn.

9. The method for determining the pesticide residue in tea according to claim 8, characterized in that: The pesticides to be tested include: glyphosate, glufosinate, methomyl, carbendazim, thiamethoxam, imidacloprid, trihydroxycarbofuran, carbofuran, acetamiprid, diflubenzuron, phoxim, and indoxacarb.

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