A method for determining the pesticide residue in tea

Abstract

The present invention relates to the technical field of pesticide detection, and specifically relates to a method for determining the pesticide residue content in tea, including sample pretreatment, sample purification, matrix calibration, and correction of the detection results based on a calibration curve. By optimizing the sample pretreatment, purification, and detection steps, this method can effectively reduce the matrix effect of tea and improve the accuracy and reliability of the determination of pesticide residue content in tea. At the same time, 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. The method described in the present invention has a reasonable operation process, can quickly and accurately determine the pesticide residue content in tea, and provides strong technical support for the supervision of tea quality and safety, quality control, and consumer health protection.

Description

Technical Field

[0001] The invention relates to the technical field of pesticide detection, and in particular to a method for determining pesticide residues 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 received increasing attention, especially for tea, an agricultural product widely consumed in people's daily lives. The accurate determination of its pesticide residues is crucial to ensure food safety and consumer health.

[0003] Tea is a complex biological matrix, and its components may interfere with the detection of pesticides, resulting in deviations in the test results. It is difficult to effectively purify the matrix in tea leaves during the extraction and purification stages, resulting in a large impact of the tea matrix content on the determination. In addition, existing detection technologies make it difficult to combine glyphosate and glufosinate with other pesticides for detection, resulting in complicated and cumbersome steps for pesticide residue determination.

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

[0005] The present invention aims to provide a method for determining the amount of pesticide residues in tea leaves, thereby improving the accuracy and reliability of the determination of the amount of pesticide residues in tea leaves.

[0006] In order to solve the above technical problems, the technical solutions provided by the present invention are as follows:

[0007] A method for determining pesticide residues in tea, comprising the following steps:

[0008] S1. Sample pretreatment:

[0009] Grind the tea leaves and extract them with water and acetonitrile in turn to obtain extract A and extract B respectively;

[0010] S2. Sample purification:

[0011] 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 two purified liquids are combined, mixed thoroughly, and then C18 powder and GCB powder are added for centrifugal treatment. The supernatant is taken and dried by blowing nitrogen;

[0012] S3. Detection of samples using liquid chromatography-tandem mass spectrometry:

[0013] Dissolve the dried residue obtained in step S2 with a mixed solution of acetonitrile and water. After filtration through a microporous membrane, perform liquid chromatography separation on a C18 chromatographic column with gradient elution, and then use a mass spectrometer for detection;

[0014] S4. Matrix calibration:

[0015] Prepare the matrix extraction solution of blank sample tea and the standard solution of the pesticide to be detected 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 plot the standard curve after matrix calibration;

[0016] S5. Correct the detection results based on the calibration curve:

[0017] Put the characteristic ion peak areas of each pesticide in the tea sample detected in step S3 into the corresponding pesticide standard curve to obtain the accurate concentration values of each pesticide in the sample.

[0018] As an improvement, the specific steps of the sample pretreatment in step S1 are:

[0019] Grind the tea into powder, then weigh 2 g of the tea powder, add 15 mL of deionized water, perform ultrasonic extraction for 30 min under the condition of a 45 °C water bath, and perform suction filtration to obtain the extraction solution, denoted as extraction solution A;

[0020] Put the filter residue obtained by 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 to 5 mL by nitrogen blowing, denoted as extraction solution B.

[0021] As an improvement, the specific steps of the sample pretreatment in step S2 are:

[0022] S2-1. Purification of extraction solution A:

[0023] Add 20 mL of dichloromethane to the centrifuge tube of extraction solution A, place it on a vortex oscillator for high-speed vortex mixing for 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;

[0024] S2-2. Purification of extraction solution B:

[0025] Add 60 - 80 mg of PSA powder to the extraction solution B. After thorough mixing, 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 supernatant and label it as the purified solution B;

[0026] S2 - 3. Combine and purify:

[0027] Combine the purified solution A and the purified solution B, then add 30 - 80 mg each of C18 powder and GCB powder. After thorough mixing, centrifuge at 10000 r / min for 5 min. Take the supernatant and dry it by blowing nitrogen.

[0028] As an improvement, in step S3, the volume fractions of acetonitrile and water in the acetonitrile - water mixed solution are 40% and 60% respectively.

[0029] As an improvement, in step S3, the column temperature of the chromatographic column 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; among them, mobile phase A is an aqueous solution of 0.1% formic acid and 4 mmol / L ammonium acetate, and mobile phase B is acetonitrile.

[0030] As an improvement, the gradient elution sequence 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%.

[0031] As an improvement, the mass spectrometry conditions in step S3 are as follows:

[0032] Ion source: electrospray ionization source (ESI);

[0033] Scanning mode: positive and negative ion switching scanning mode;

[0034] Detection mode: multiple reaction monitoring (MRM) mode;

[0035] Spray voltage: positive ion spray voltage: 2500 V, negative ion spray voltage: - 2000 V;

[0036] Atomization temperature: 290 - 300 °C, ion transfer tube temperature: 285 °C, sheath gas flow rate: 60 arb, auxiliary gas flow rate: 15 arb.

[0037] As an improvement, the method of matrix calibration described in step S4 is as follows:

[0038] First, prepare the matrix extraction solution. Weigh 10.0 g of tea samples 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 the complete 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;

[0039] Weigh the pesticide standard samples to be detected. Transfer 1 mL of each pesticide standard sample into a 50 mL volumetric flask respectively, and dilute to the mark with ethyl acetate to prepare a mixed standard solution with a concentration of 2 mg / L. Take the mixed standard solution and use ethyl acetate to gradually 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 respectively;

[0040] 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 sample, and draw a standard curve calibrated by the matrix.

[0041] As an improvement, the pesticides to be detected include: glyphosate, glufosinate, methomyl, carbendazim, thiamethoxam, imidacloprid, carbofuran, carbaryl, acetamiprid, diflubenzuron, phoxim, indoxacarb.

[0042] The advantages of the present invention are as follows:

[0043] 1. By optimizing the sample pretreatment steps, the present invention uses water and acetonitrile to extract pesticide residues in tea respectively, which can extract pesticides with different properties more comprehensively and improve the extraction efficiency. In the treatment of extraction solution A, ultrasonic extraction in a 45 °C water bath combined with subsequent suction filtration operations can effectively separate water-soluble pesticide components; while extraction solution B is extracted by acetonitrile and salts such as sodium chloride, anhydrous magnesium sulfate, and anhydrous sodium acetate are added. Utilizing the salting-out effect and centrifugation operations, 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, improving the convenience of pesticide detection while ensuring the accuracy of pesticide detection.

[0044] 2. In the sample purification step of the present invention, the extraction solution A containing glyphosate and glufosinate and the extraction solution B containing other pesticides are purified separately, which can effectively remove the tea matrix in the extraction solutions. After purification, the two are combined and purified through 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 tea polyphenols and other matrices in the original extraction solution A, avoiding interference of the tea matrix on pesticide determination.

[0045] 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 pesticide components, the present invention specifically configures the ratio of the acetonitrile - water mixed solution, so that various pesticides can be repeatedly dissolved in the mixed solution.

[0046] 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 detected pesticide, and mixing the two to prepare matrix calibration solutions with different concentrations, the matrix environment in the actual sample is simulated, so that 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, a more accurate pesticide concentration value can be obtained, improving the reliability of the detection results.

[0047] 5. The method described in the present invention has a reasonable operation process, with each step closely connected, and is easy to be popularized and applied in actual detection work. From the grinding, extraction, purification of the sample to the detection and result analysis, the whole process is standardized and efficient. It can achieve rapid and accurate determination of pesticide residues in tea leaves on the premise of ensuring the detection quality, providing strong technical support for the supervision of tea quality and safety, quality control, and the protection of consumers' health. Specific Embodiments

[0048] 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.

[0049] A method for determining the pesticide residue in tea leaves includes the following steps:

[0050] S1. Sample pretreatment:

[0051] Grind the tea leaves into powder, then weigh 2 g of the tea leaf powder, accurate to 0.001 g, add it to 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, and filter to obtain the extract, denoted as extract A.

[0052] Extract A is extracted with deionized water, mainly used to extract pesticides with large polarity, which are easily soluble in water and difficult to dissolve in organic solvents, such as glyphosate or glufosinate - ammonium.

[0053] Add the filter residue obtained by 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 to 5 mL by nitrogen blowing, denoted as extraction solution B.

[0054] The filter residue can be ultrasonically extracted with acetonitrile to extract carbamate pesticides in the filter residue, such as carbofuran, methomyl, etc., and organophosphorus pesticides with slightly weaker polarity.

[0055] S2. Sample purification:

[0056] Purify extraction solution A and extraction solution B respectively.

[0057] Add 20 mL of dichloromethane to the centrifuge tube of extraction solution A, place it on a vortex oscillator for high-speed vortex mixing, and the mixing time is 30 - 60 s to make dichloromethane fully contact and mix with extraction solution A, promoting the dissolution of glyphosate and the full extraction of impurities. Then place it in a centrifuge and centrifuge at a speed of 8000 - 10000 r / min for 3 - 5 min. After centrifugation, the mixed solution is divided into two layers, the upper layer is an aqueous solution containing glyphosate, and the lower layer is a dichloromethane phase. Take the upper aqueous phase and denote it as purified solution A.

[0058] Since extraction solution A is extracted with deionized water, it contains more impurity components. The caffeine, alkaloids and other components in extraction solution A can be removed by shaking extraction with dichloromethane, reducing the interference of corresponding impurities on subsequent detection.

[0059] The purification method of extraction solution B is as follows: 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 the above extraction solution A. After centrifugation, take the upper clear liquid and denote it as purified solution B. PSA (N-propylethylenediamine) is suitable for the adsorption of polar compounds and can effectively reduce the polar impurities in extraction solution B.

[0060] Combine purified solution A and purified solution B, and then add 30 - 80 mg each of C 18 powder and GCB powder, mix well, centrifuge at 10000 r / min in a centrifuge for 5 min, take the upper clear liquid, and dry it by nitrogen blowing.

[0061] S3. Detect the sample using liquid chromatography-tandem mass spectrometry:

[0062] Dissolve the dried residue obtained in step S2 with 3 mL of a mixed solution of acetonitrile and water. After filtration through a microporous filter membrane, perform liquid chromatography separation using a C 18 chromatographic column. The volume fractions of acetonitrile and water in the mixed solution of acetonitrile and water are 40% and 60% respectively, and the pore size during microporous filtration is 0.2 μm.

[0063] During chromatographic column separation, the column temperature is 40 °C, the injection volume is 10 μL, and the flow rate is 0.3 mL / min; gradient elution is performed. The mobile phase consists of mobile phase A and mobile phase B; among them, mobile phase A is an aqueous solution of 0.1% formic acid and 4 mmol / L ammonium acetate, and mobile phase B is acetonitrile.

[0064] 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%.

[0065] The mass spectrometry conditions are as follows:

[0066] Ion source: electrospray ionization source (ESI).

[0067] Scanning mode: positive and negative ion switching scanning mode.

[0068] Detection mode: multiple reaction monitoring (MRM) mode.

[0069] Spray voltage: positive ion spray voltage: 2500 V, negative ion spray voltage: -2000 V.

[0070] Atomization temperature: 290 - 300 °C. Ion transfer tube temperature: 285 °C. Sheath gas flow rate: 60 arb, auxiliary gas flow rate: 15 arb.

[0071] S4. Matrix calibration:

[0072] 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 to form 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 to obtain the matrix extraction solution.

[0073] Weigh 12 pesticide standards. Transfer 1 mL of each of the 12 pesticide standards (100 mg / L) into a 50 mL volumetric flask, and make up the volume to the mark with ethyl acetate to prepare a mixed standard solution with a concentration 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.

[0074] 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) to plot the standard curves of the 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.

[0075] S5. Correct the test results based on the calibration curve:

[0076] Substitute the characteristic ion peak areas of each pesticide in the tea samples detected in step S3 into the standard curves of the corresponding pesticides to obtain the accurate concentration values of each pesticide in the samples. The calculation formula is as follows:

[0077]

[0078] 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, with the unit of 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, with the unit of g.

[0079] Example 1

[0080] S1. Sample pretreatment:

[0081] Take green tea as the experimental research object, grind the green tea into powder, weigh 2 g of the tea powder, add it to a centrifuge tube, add 15 mL of deionized water, ultrasonically extract for 30 min under the condition of a 45°C water bath, and filter to obtain extract A.

[0082] 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, perform a water bath at 45°C, and concentrate to 5 mL by nitrogen blowing to obtain extract B.

[0083] S2. Sample purification:

[0084] Add 20 mL of dichloromethane to the extraction solution A, vortex mix for 60 s on a vortex oscillator, then centrifuge at 10000 r / min for 3 min, and take the upper aqueous phase as the purified solution A.

[0085] Add 80 mg of PSA powder to the extraction solution B, mix well, centrifuge at 10000 r / min for 3 min, and take the upper clear liquid as the purified solution B. Combine the purified solution A and the purified solution B, add 80 mg each of C18 powder and GCB powder, mix well, centrifuge at 10000 r / min for 5 min, take the upper clear liquid, and dry it by blowing nitrogen.

[0086] S3. Detect the sample using liquid chromatography - tandem mass spectrometry:

[0087] 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 on 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.

[0088] S4. Matrix calibration:

[0089] 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, plot the standard curve after matrix calibration.

[0090] Table 1 Mass spectrometry parameters of pesticides in tea

[0091]

[0092] S5. Calibration and correction of the detection results:

[0093] 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:

[0094]

[0095] 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.

[0096] After the correction, calculate the recovery rate and repeat it 6 times. The recovery rate and detection limit are given in Table 2.

[0097] Table 2 Recovery rate and detection limit of 12 pesticides

[0098]

[0099] The above data show that the recovery rate of this detection method for the 12 pesticide residues in green tea is between 75% - 95% at different concentrations, and the relative standard deviation is between 3.4% - 7.7%, meeting the verification requirements of the pesticide residue detection method, proving that this scheme is effective.

[0100] The above is only a preferred specific embodiment 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, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for determining the pesticide residue in tea, characterized in that, It includes the following steps: S1. Sample pretreatment: Grind the tea leaves into powder, then weigh 2 g of the tea leaf powder, add 15 mL of deionized water, and perform ultrasonic extraction for 30 min under the condition of a 45°C water bath. Filter by suction to obtain the extract, denoted as extract 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 extracts, and then concentrate by nitrogen blowing to 5 mL, denoted as extract B; S2. Sample purification: S2-1. Purification of extract A: Add 20 mL of dichloromethane to the centrifuge tube of extract A, place it on a vortex oscillator for high-speed vortex mixing for 30 - 60 s, then place it in a centrifuge and centrifuge at a speed of 8000 - 10000 r / min for 3 - 5 min, and take the upper aqueous phase, denoted as purified liquid A; S2-2. Purification of extract B: Add 60 - 80 mg of PSA powder to extract B, mix well, and centrifuge at 8000 - 10000 r / min for 3 - 5 min. After centrifugation, take the upper clear liquid and denote it as purified liquid B; S2-3. Combined purification: Combine purified liquid A and purified liquid B, then add 30 - 80 mg of C18 powder and GCB powder each, mix well, centrifuge at 10000 r / min in a centrifuge for 5 min, take the upper clear liquid, and dry it by nitrogen blowing; S3. Detect the sample using liquid chromatography - tandem mass spectrometry: Dissolve the dried residue obtained in step S2 with a mixed solution of acetonitrile - water, filter it through a microporous filter membrane, perform liquid chromatography separation with a C18 chromatographic column, gradient elution, and then detect it using a mass spectrometer; The column temperature of the chromatographic column is 40°C, the injection volume is 10 μL, and the flow rate is 0.3 mL / min; perform gradient elution, and the mobile phase consists of mobile phase A and mobile phase B; among them, mobile phase A is an aqueous solution of 0.1% formic acid and 4 mmol / L ammonium acetate, and mobile phase B is acetonitrile; The said 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%; S4. Matrix calibration: Respectively prepare the matrix extract of blank sample tea leaves and the standard solution of the detected pesticide, 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 standard curve of the corresponding pesticide to obtain the accurate concentration values of each pesticide in the sample; The pesticides include: glyphosate, glufosinate, methomyl, carbendazim, thiamethoxam, imidacloprid, carbofuran-3-hydroxy, carbofuran, acetamiprid, diflubenzuron, phoxim, indoxacarb.

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

3. The method for determining the pesticide residue content in tea according to claim 1, wherein The mass spectrometry conditions of the liquid chromatography-tandem mass spectrometry method 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.

4. The method for determining the pesticide residue content in tea according to claim 1, characterized in that, The method of matrix calibration in step S4 is as follows: First, prepare the matrix extraction solution. Weigh 10.0 g of tea samples 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 for ultrasonic extraction for 15 min, and 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 samples to be detected. Transfer 1 mL of each pesticide standard sample into a 50 mL volumetric flask respectively, dilute to the mark with ethyl acetate to prepare a mixed standard solution with a concentration of 2 mg / L. Take the mixed standard solution and prepare a series of mixed standard solutions with mass concentrations of 10 μg / L, 50 μg / L, and 100 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 sample, and draw a standard curve after matrix calibration.

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