Method for determining residual quantity of picoxystrobin, flufenoxuron, fenazaquin and buprofezin in tea leaves

Abstract

The invention discloses a method for determining residual quantity of picoxystrobin, flufenoxuron, fenazaquin and buprofezin in tea, the determination method is a gas chromatography-tandem mass spectrometry method, and the method comprises the following steps: (1) preparing a standard stock solution and a standard working solution; (2) preparing a sample to be detected; (3) setting gas chromatography-tandem mass spectrometry analysis conditions; (4) drawing a standard curve; and (5) calculating a result. The invention establishes a method for determining the residual quantity of picoxystrobin, flufenoxuron, fenazaquin and buprofezin in tea leaves by using gas chromatography-tandem mass spectrometry. The method fills up the blank that the prior art cannot simultaneously detect the items of picoxystrobin, flufenoxuron, fenazaquin and buprofezin, has the characteristics of good selectivity, high sensitivity, strong background interference resistance and the like, and is suitable for daily detection of residual quantity of picoxystrobin, flufenoxuron, fenazaquin and buprofezin in tea.

Description

Technical Field

[0001] The present invention relates to a method for determining the residues of picoxystrobin, flufenoxuron, quinothiophan, and buprofezin in tea. Background Art

[0002] Flufenoxuron, quinothiophan, buprofezin, and picoxystrobin are all common agricultural pesticides in China and are widely used to control crop pests and diseases. The national standard for the maximum residue limits of pesticides in foods in China (GB 2763-2021) stipulates the maximum residue limits of picoxystrobin, flufenoxuron, quinothiophan, and buprofezin in tea (the limit values are 20 mg / kg for picoxystrobin, 20 mg / kg for flufenoxuron, 15 mg / kg for quinothiophan, and 10 mg / kg for buprofezin respectively). However, there is currently no detection method that can simultaneously detect picoxystrobin, flufenoxuron, quinothiophan, and buprofezin in tea. Once the detection of the above items is involved, multiple methods need to be used for simultaneous determination, which not only consumes time but also a large amount of reagent consumables. In addition, the existing gas chromatography-tandem mass spectrometry standards for the above items all use the selected ion monitoring (SIM) mode, which has limitations in terms of selectivity, sensitivity, and anti-background interference. Therefore, it is of great significance to invent a detection method that can simultaneously detect the residues of picoxystrobin, flufenoxuron, quinothiophan, and buprofezin in tea and has the characteristics of good selectivity, high sensitivity, and strong anti-background interference ability for the detection of pesticide residues in tea on the market. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for determining the residues of picoxystrobin, flufenoxuron, quinothiophan, and buprofezin in tea, which is used to fill the blank of the detection method that can simultaneously detect picoxystrobin, flufenoxuron, quinothiophan, and buprofezin in tea, and makes the method have the characteristics of good selectivity, high sensitivity, and strong anti-background interference ability by using the multiple reaction monitoring mode.

[0004] To achieve the above purpose, the technical solution of the present invention is as follows: The method for determining the residues of picoxystrobin, flufenoxuron, quinothiophan, and buprofezin in tea according to the present invention specifically comprises the following steps: (1) Preparation of standard stock solution and standard working solution: The standard stock solutions of picoxystrobin, flufenoxuron, quinothiophos, and buprofezin are all standard stock solutions with a concentration of 100 μg / mL. The standard stock solution is diluted with acetonitrile to a mixed standard working solution with a concentration of 1 μg / mL. The mixed standard working solution of picoxystrobin, flufenoxuron, quinothiophos, and buprofezin is prepared into a series of mixed standard working solutions with concentrations of 0.0020 μg / mL, 0.0050 μg / mL, 0.0100 μg / mL, 0.0500 μg / mL, 0.100 μg / mL, 0.200 μg / mL, and 0.500 μg / mL by stepwise dilution with tea blank matrix solution. (2) Preparation of test sample: Weigh 2 g of the test sample (accurate to 0.01 g) into a 50 mL plastic centrifuge tube, add 10 mL of water, vortex to mix evenly, and let it stand for 30 min. Add 15 mL of acetonitrile + acetic acid (99 + 1) solution, 6 g of anhydrous magnesium sulfate, and 1 ceramic homogenizer. Cover the centrifuge tube cap, shake vigorously for 1 min, and then centrifuge at 4200 r / min for 5 min. Pipette 8 mL of the supernatant into a 15 mL plastic centrifuge tube containing 1200 mg of anhydrous magnesium sulfate, 400 mg of PSA, 400 mg of C18, and 50 mg of GCB. Vortex to mix evenly for 1 min, and then centrifuge at 4200 r / min for 5 min. Accurately pipette 4 mL of the supernatant into a 10 mL test tube, and blow it to nearly dry with nitrogen in a 40℃ water bath environment. Add 1 mL of ethyl acetate for reconstitution, and filter through a microporous filter membrane for determination.

[0005] (3) The instrument used was a gas chromatography-tandem mass spectrometer. Gas chromatography conditions: Chromatographic column: 5% cyanopropylphenyl-95% dimethylpolysiloxane fused silica capillary column: 30 m × 0.25 mm × 0.25 μm; Column temperature: Hold at 60 °C for 1 min, then program the temperature to rise at a rate of 40 °C / min to 170 °C, and then rise at a rate of 10 °C / min to 310 °C and hold for 5 min; Carrier gas: Helium, purity ≥ 99.999%, flow rate 1.0 mL / min; Injector temperature: 280 °C; Injection volume: 1 μL; Injection mode: Splitless injection; Mass spectrometry conditions: Ion source type: Electron impact ionization source (EI): 70 eV; Ion source temperature: 280 °C; Transfer line temperature: 280 °C; Solvent delay: 3 min; Multiple reaction monitoring; Detection ion pair mass spectrometry parameters: Flufenoxuron (retention time 8.81 min, ion pair I: 126.0 / 98.0, collision energy 20 V, ion pair II: 126.0 / 80.0, collision energy 10 V); Buprofezin (retention time 12.04 min, ion pair I: 104.0 / 51.0, collision energy 25 V, ion pair II: 104.0 / 77.0, collision energy 25 V); Picoxystrobin (retention time 11.54 min, ion pair I: 145.0 / 102.1, collision energy 25 V, ion pair II: 145.0 / 115.1, collision energy 15 V); Fenazaquin (retention time 11.53 min, ion pair I: 145.0 / 117.1, collision energy 10 V, ion pair II: 160.0 / 117.1, collision energy 20 V); (4) Preparation of the standard curve: The series of mixed standard working solutions of flufenoxuron, buprofezin, picoxystrobin, and fenazaquin were injected into the gas chromatography-tandem mass spectrometer and detected under the chromatographic and mass spectrometry conditions of step (3). Qualitative analysis was performed based on the retention time and ion pairs, and the standard curve formula Z = FW + G was plotted according to the corresponding relationship between the peak area of the compound measured at each concentration and its mass concentration. Here, Z: the concentration of the compound to be measured, unit μg / mL; W is the peak area of the compound to be measured obtained on the instrument through sample injection; F is the slope of the standard curve plotted by the instrument according to the corresponding relationship between the peak area of the compound and its concentration; G is the intercept of the standard curve plotted by the instrument according to the corresponding relationship between the peak area of the compound and its concentration; (5) Result calculation: The sample obtained in (2) was taken into the gas chromatography-tandem mass spectrometer and detected under the chromatographic and mass spectrometry conditions of step (3). The peak areas of the quantitative ions of flufenoxuron, buprofezin, picoxystrobin, and fenazaquin in the sample were measured. Qualitative analysis was performed based on the retention time and ion pairs, and quantitative analysis was carried out according to the standard curve plotted in (4) to calculate the residue amounts of flufenoxuron, buprofezin, picoxystrobin, and fenazaquin in the sample.

[0006] Compared with the prior art, the present invention has the following outstanding advantages: The present invention fills the blank of the detection method for simultaneously detecting picoxystrobin, flufenoxuron, quinothionate, and buprofezin in tea in the current prior art. Only one pretreatment and one machine test are required to complete the simultaneous determination of picoxystrobin, flufenoxuron, quinothionate, and buprofezin in tea; The present invention uses the multiple reaction monitoring (MRM) mode. Compared with the selected ion monitoring (SIM) mode used in the existing standards, this method has the characteristics of good selectivity, high sensitivity, and strong anti-background interference ability; The present invention adopts the QuEChERS sample pretreatment rapid technology. Compared with the conventional pretreatment methods, this method has low cost, simple operation, short pretreatment time, high recovery rate, precision, and accuracy, a wide range of pesticides that can be analyzed, less solvent usage, and less environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is the multiple reaction monitoring (MRM) ion chromatogram of picoxystrobin.

[0008] Figure 2 It is the multiple reaction monitoring (MRM) ion chromatogram of flufenoxuron.

[0009] Figure 3 It is the multiple reaction monitoring (MRM) ion chromatogram of quinothionate.

[0010] Figure 4 It is the multiple reaction monitoring (MRM) ion chromatogram of buprofezin. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be further described below through specific examples. EXAMPLE

[0012] 1 Reagents and Materials Unless otherwise specified, only analytical pure reagents are used in the analysis, and all test water is the first-class water specified in GB / T 6682.

[0013] 1.1 Reagents 1.1.1 Acetonitrile (CH3CN).

[0014] 1.1.2 Ethyl acetate (CH3COOC2H5).

[0015] 1.1.3 Acetic acid (CH3COOH).

[0016] 1.1.4 Anhydrous magnesium sulfate (MgSO4).

[0017] 1.2 Solution Preparation 1.2.1 Acetonitrile - acetic acid solution (99 + 1): Measure 10 mL of acetic acid and add it to 990 mL of acetonitrile, then mix well.

[0018] 1.3 Standards Standard stock solutions of flufenoxuron (CAS No.: 101463 - 69 - 8), buprofezin (CAS No.: 69327 - 76 - 0), picoxystrobin (CAS No.: 117428 - 22 - 5), and quinothrin (CAS No.: 120928 - 09 - 8), with a concentration of 100 μg / mL each, are provided by Fujian Chemical Glass Science and Education Instrument Co., Ltd.

[0019] 1.4 Preparation of standard solutions Preparation of standard stock solutions and standard working solutions: Dilute the standard stock solutions with acetonitrile to prepare a mixed standard working solution with a concentration of 1 μg / mL. Then, use the blank matrix solution of tea leaves to prepare a series of mixed standard working solutions with concentrations of 0.0020 μg / mL, 0.0050 μg / mL, 0.0100 μg / mL, 0.0500 μg / mL, 0.100 μg / mL, 0.200 μg / mL, and 0.500 μg / mL for picoxystrobin, flufenoxuron, quinothrin, and buprofezin by step - by - step dilution method. All standard working solutions and standard stock solutions are stored in a refrigerator at 0 °C - 4 °C in the dark.

[0020] 1.5 Materials 1.5.1 Ethylenediamine - N - propylsilylated silica gel (PSA): 40 μm - 60 μm.

[0021] 1.5.2 Octadecylsilane - bonded silica gel (C18): 40 μm - 60 μm.

[0022] 1.5.3 Graphitized carbon black (GCB): 40 - 120 μm.

[0023] 1.5.4 Ceramic homogenizer: 2 cm (length) × 1 cm (outer diameter).

[0024] 1.5.5 Microporous filter membrane (organic phase): 13 mm × 0.22 μm.

[0025] 2 Instruments and equipment 2.1 Gas chromatography - tandem mass spectrometer: Equipped with an electron impact source (EI).

[0026] 2.2 Analytical balance: With a sensitivity of 0.1 mg and 0.01 g.

[0027] 2.3 Centrifuge: With a rotation speed of not less than 4200 r / min.

[0028] 2.4 Tissue homogenizer.

[0029] 2.5 Nitrogen blower: Temperature controllable.

[0030] 2.6 Vortex mixer.

[0031] 3 Method 3.1 Reference conditions for gas chromatography determination Chromatographic column: 5% cyanopropylphenyl - 95% dimethylpolysiloxane fused silica capillary column: 30 m × 0.25 mm × 0.25 μm; Column temperature: Hold at 60 °C for 1 min, then program - raise the temperature to 170 °C at a rate of 40 °C / min, and then raise the temperature to 310 °C at a rate of 10 °C / min and hold for 5 min; Carrier gas: Helium, purity ≥ 99.999%, flow rate 1.0 mL / min; Injector temperature: 280 °C; Injection volume: 1 μL; Injection mode: Splitless injection.

[0032] 3.2 Mass spectrometry reference conditions Ion source type: Electron impact source (EI): 70 eV; Ion source temperature: 280 °C; Transfer line temperature: 280 °C; Solvent delay: 3 min; Multiple reaction monitoring: For each pesticide, select a pair of quantitative ions and a pair of qualitative ions respectively. All the required ion pairs in each group are detected separately in time periods according to the elution order. The retention time, quantitative ion pairs, qualitative ion pairs and collision voltages of each pesticide are shown in Table 1.

[0033] Table 1 Mass spectrometry parameters of detected ion pairs

[0034] 3.3 Drawing of matrix standard working curve Inject the series of mixed standard working solutions of flufenoxuron, buprofezin, picoxystrobin, and quinothrin onto a gas chromatography - tandem mass spectrometer, and conduct the determination according to the chromatographic and mass spectrometry conditions in 3.1 - 3.2. Identify by retention time and ion pairs, and draw a standard curve based on the corresponding relationship between the peak area of the compound measured at each concentration and its mass concentration. The standard curve formula is Z = FW + G, where Z: concentration of the compound to be measured, unit μg / mL; W is the peak area of the compound to be measured obtained on the instrument through sample injection; F is the slope of the standard curve drawn by the instrument according to the corresponding relationship between the compound peak area and its concentration; G is the intercept of the standard curve drawn by the instrument according to the corresponding relationship between the compound peak area and its concentration.

[0035] 4 Sample testing procedures 4.1 Sample Preparation and Storage The tea leaves are crushed at room temperature and thoroughly mixed, then put into a polyethylene bottle or bag. The sample is stored at -18 °C for future use.

[0036] 4.2 Sample Pretreatment Weigh 2 g of the sample (accurate to 0.01 g) into a 50 mL plastic centrifuge tube, add 10 mL of water, vortex to mix evenly, and let it stand for 30 min. Then add 15 mL of acetonitrile + acetic acid (99 + 1) solution, 6 g of anhydrous magnesium sulfate, and 1 ceramic homogenizer. Cover the centrifuge tube cap, shake vigorously for 1 min, and then centrifuge at 4200 r / min for 5 min. Pipette 8 mL of the supernatant into a 15 mL plastic centrifuge tube containing 1200 mg of anhydrous magnesium sulfate, 400 mg of PSA, 400 mg of C18, and 50 mg of GCB. Vortex to mix evenly for 1 min, then centrifuge at 4200 r / min for 5 min. Accurately pipette 4 mL of the supernatant into a 10 mL test tube, and blow it to near dry with nitrogen in a 40 °C water bath environment. Add 1 mL of ethyl acetate to redissolve it, and filter through a microporous filter membrane for determination.

[0037] 4.3 Sample Testing Inject the sample solution into the gas chromatography - tandem mass spectrometer in sequence. Qualify by retention time and ion pairs, measure the peak area of the quantitative ion. The response value of the compound in the sample solution to be measured should be within the linear range of quantitative determination by the instrument. When it exceeds the linear range, it should be diluted by an appropriate multiple according to the measured concentration and then analyzed again.

[0038] 4.4 Qualification and Quantification 4.4.1 Retention Time Compare the retention time of the chromatographic peak of the target pesticide in the tested sample with that of the corresponding standard chromatographic peak. The relative error should be within ± 0.1 min.

[0039] 4.4.2 Ion Abundance Ratio When performing sample determination under the same experimental conditions, if the retention time of the detected chromatographic peak is consistent with that of the standard sample, and in the mass spectrum of the sample after background subtraction, both the mass spectrometric quantitative and qualitative ions of the target compound appear, and for the same compound in the same detection batch, the relative abundance ratio of the qualitative and quantitative ions of the target compound in the sample compared with the matrix standard solution with a comparable mass concentration, its allowable deviation does not exceed the range specified in Table 2, then it can be judged that the target pesticide exists in the sample.

[0040] Table 2 Maximum Allowable Deviation of Relative Ion Abundance during Qualification

[0041] 4.4.3 Quantification Quantification by external standard method.

[0042] 5 Result calculation The pesticide residue content in the sample is represented by X, and the value is represented by milligrams per kilogram (mg / kg), and is calculated according to the following formula:

[0043] In the formula: X: The content of the analyte in the sample, unit is milligrams per kilogram (mg / kg); C: The mass concentration of the analyte in the matrix-matched standard working solution, unit is micrograms per liter (μg / mL); A: The peak area of the analyte in the sample solution; A S : The peak area of the analyte in the matrix-matched standard working solution; V: The volume by which the sample is diluted during the test, unit is milliliters (mL); m: The sample weighing amount, unit is grams (g); The calculation result is expressed as the arithmetic mean of 2 independent determinations obtained under repeatability conditions, retaining 2 significant figures, and retaining 3 significant figures when the content exceeds 1 mg / kg.

[0044] 6 Methodology investigation: including linearity, detection limit, quantification limit, recovery rate, precision.

[0045] 6.1 Linearity, detection limit, quantification limit: Prepare a series of mixed standard working solutions with concentrations of flufenoxuron, buprofezin, picoxystrobin, and quinothrin ranging from 0.0020 μg / mL to 0.500 μg / mL, perform linear regression with the peak area against the concentration, and the linear equation and correlation coefficient are shown in Table 3. The results show that flufenoxuron, buprofezin, picoxystrobin, and quinothrin have good linear relationships within the range of 0.0020 μg / mL to 0.500 μg / mL, and the correlation coefficient R is greater than 0.999. The method fully meets the detection requirements for the residues of flufenoxuron, buprofezin, picoxystrobin, and quinothrin in tea. The detection limit and quantification limit of the method are shown in Table 4.

[0046] Table 3 Linearity range, regression equation, and correlation coefficient of flufenoxuron, buprofezin, picoxystrobin, and quinothrin

[0047] Y: Peak area; x: Mass concentration, μg / mL.

[0048] Table 4 Method detection limit and quantification limit of flufenoxuron, buprofezin, picoxystrobin, and quinothrin

[0049] 6.2 Recovery rate and precision: Under the optimized detection conditions, blank matrix tea samples were taken for spiked recovery tests. The spiked levels were 0.005 mg / kg, 0.01 mg / kg, and 0.05 mg / kg respectively, and each level was analyzed 6 times. The results are shown in Table 5. It can be seen from Table 5 that the spiked recovery rate range of this method is 79.2% - 91.4%, and the relative standard deviation RSD range is 2.9% - 4.3%. The results show that this method is applicable to the routine analysis and detection of the residues of flufenoxuron, buprofezin, picoxystrobin, and fenazaquin in tea.

[0050] Table 5 Experimental results of spiked recovery of tea samples (n = 6)

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for detecting the residual amount of picoxystrobin, flufenoxuron, quinazofen and buprofezin in tea, characterized in that , the specific steps of the determination method are as follows: (1) Preparation of standard stock solutions and standard working solutions: The standard stock solutions of picoxystrobin, flufenoxuron, quinazoline and thiamethoxam are all 100 μg / mL standard stock solutions. The standard stock solutions are prepared with acetonitrile to prepare a mixed standard working solution with a concentration of 1 μg / mL. The mixed standard working solutions of picoxystrobin, flufenoxuron, quinazoline and thiamethoxam are prepared with tea blank matrix solution by stepwise dilution method to prepare a series of mixed standard working solutions with concentrations of 0.0020 μg / mL, 0.0050 μg / mL, 0.0100 μg / mL, 0.0500 μg / mL, 0.100 μg / mL, 0.200 μg / mL and 0.500 μg / mL; (2) Preparation of the sample to be tested: Weigh 2 g of the sample (accurate to 0.01 g) into a 50 mL plastic centrifuge tube, add 10 mL of water and vortex to mix, and let stand for 30 min. Add 15 mL of acetonitrile + acetic acid (99+1) solution, 6 g of anhydrous magnesium sulfate, and 1 ceramic homogenizer, cover the centrifuge tube, shake vigorously for 1 min, and centrifuge at 4200 r / min for 5 min. Pipette 8 mL of supernatant and add it to a 15 mL plastic centrifuge tube containing 1200 mg anhydrous magnesium sulfate, 400 mg PSA, 400 mg C18, and 50 mg GCB. Vortex mix for 1 min and centrifuge at 4200 r / min for 5 min. Accurately pipette 4 mL of supernatant into a 10 mL test tube and blow it to near dryness with nitrogen in a 40°C water bath. Add 1 mL of ethyl acetate to reconstitute, pass through a microporous filter membrane, and use for determination; (3) The instrument used was a gas chromatography-tandem mass spectrometer. The gas chromatography conditions were as follows: chromatographic column: 5% propyl cyanophenyl-95% dimethylpolysiloxane quartz capillary column: 30 m×0.25 mm×0.25 μm; chromatographic column temperature: 60 °C for 1 min, then programmed to 170 °C at 40 °C / min, then programmed to 310 °C at 10 °C / min, and maintained for 5 min; Carrier gas: helium, purity ≥99.999%, flow rate 1.0 mL / min; injection port temperature: 280 ℃; injection volume: 1 μL; injection mode: splitless injection; mass spectrometry conditions: ion source type: electron impact source (EI): 70 eV; ion source temperature: 280 ℃; transfer line temperature: 280 ℃; solvent delay: 3 min; multiple reaction monitoring; detection ion pair mass spectrometry parameters: flufenoxuron (retention time 8.81 min, ion pair I: 126.0 / 98.0, collision energy 20 V, ion pair II: 126.0 / 80.0, collision energy 10 V); thiamethoxam (retention time 12.04 min, ion pair I: 104.0 / 51.0, collision energy 25 V, ion pair II: 104.0 / 77.0, collision energy 25 V); picoxystrobin (retention time 11.54 min, ion pair Ⅰ: 145.0 / 102.1, collision energy 25 V, ion pair Ⅱ: 145.0 / 115.1, collision energy 15 V); quinazofen (retention time 11.53 min, ion pair Ⅰ: 145.0 / 117.1, collision energy 10 V, ion pair Ⅱ: 160.0 / 117.1, collision energy 20 V); (4) Drawing of standard curve: A series of mixed standard working solutions of flufenoxuron, buprofezin, picoxystrobin and quinazaquin are loaded onto a gas chromatography-tandem mass spectrometer and detected according to the chromatographic mass spectrometry conditions of step (3). The retention time and ion pair are used for qualitative analysis. The standard curve is drawn based on the corresponding relationship between the peak area of ​​the compound measured at each concentration and its mass concentration. The formula is Z=FW+G, where Z is the concentration of the compound to be tested, in units of MG / ML; W is the peak area of ​​the compound to be tested obtained on the instrument; F is the slope of the standard curve drawn by the instrument based on the corresponding relationship between the peak area of ​​the compound and its concentration; and G is the intercept of the standard curve drawn by the instrument based on the corresponding relationship between the peak area of ​​the compound and its concentration. (5) Calculation of results: Take the sample obtained in (2) and place it in a gas chromatography-tandem mass spectrometer for detection under the chromatographic mass spectrometry conditions of step (3). Measure the peak areas of the quantitative ions of flufenoxuron, buprofezin, picoxystrobin and quinazaquin in the sample, use retention time and ion pair for qualitative analysis, and use the standard curve drawn in (4) for quantitative analysis to calculate the residual amounts of flufenoxuron, buprofezin, picoxystrobin and quinazaquin in the sample.

2. The method for determining the residual amount of picoxystrobin, flufenoxuron, quinazofen and buprofezin in tea according to claim 1, characterized in that: The 8 mL supernatant described in (2) was added to a 15 mL plastic centrifuge tube containing 1200 mg anhydrous magnesium sulfate, 400 mg PSA, 400 mg C18 and 50 mg GCB for purification.

3. The method for determining the residual amount of picoxystrobin, flufenoxuron, quinazofen and buprofezin in tea according to claim 1, characterized in that: The chromatographic column described in (3) is a 5% propyl cyanoacrylate-95% dimethylpolysiloxane quartz capillary column (30 m×0.25 mm×0.25 μm), the carrier gas is helium with a purity of ≥99.999%, the ion source is an electron impact source (EI), and the multiple reaction monitoring (MRM) mode is used.

4. The method for determining the residual amount of picoxystrobin, flufenoxuron, quinazofen and buprofezin in tea according to claim 1, characterized in that: The correlation coefficient of the standard curve described in (4) is not less than 0.99.

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