A method for determining the residual amount of chlorothalonil in fruits and vegetables

Abstract

The present application belongs to the technical field of pesticide residue detection method, and particularly relates to a method for determining the chlorothalonil residue in fruits and vegetables, comprising the following steps: S1, extracting the fruit and vegetable sample by using an alkaline extraction solution to obtain an extraction solution; S2, adding a garlicin solution to the extraction solution; S3, adding a purification filler to the conversion solution, vortexing, centrifuging, filtering to obtain a to-be-tested solution; S4, using an ultra-high performance liquid chromatography-tandem mass spectrometer to detect the concentrations of mercaptochlorothalonil and 4-hydroxychlorothalonil in the to-be-tested solution, and calculating the total residue of chlorothalonil in the sample. The present application breaks through the traditional idea of inhibiting the conversion of chlorothalonil, actively promotes the complete and quantitative conversion of chlorothalonil into a single derivative through "alkaline extraction + exogenous garlicin catalysis", changes the complex and uncontrollable conversion process into a controllable and quantitative chemical reaction, and avoids the problems of low recovery rate and false negative caused by incomplete or unmeasurable conversion in principle.

Description

Technical Field

[0001] This invention relates to a method for determining the amount of chlorothalonil residue in fruits and vegetables, belonging to the technical field of pesticide residue detection methods. Background Technology

[0002] Chlorothalonil is a broad-spectrum, protective fungicide characterized by its resistance to rain washout and long-lasting efficacy. It is highly effective against fungal diseases in crops. Its molecular structure contains four chlorine atoms and two cyano groups, giving it a strong positron affinity and making it a highly reactive molecule. In complex agricultural matrices containing abundant sulfur derivative groups, such as those found in leeks and garlic, chlorothalonil readily reacts with these groups to form thiol-based chlorothalonil. This reaction significantly interferes with the extraction and detection of chlorothalonil during sample pretreatment and analysis, resulting in generally low recovery rates and severely impacting the accuracy of residue detection.

[0003] Furthermore, chlorothalonil can be degraded into its main metabolite, 4-hydroxychlorothalonil (4-hydroxy-3,5,6-trichloroisodiphenyl nitrile), under environmental conditions (such as the effects of light, water, and anthocyanins). According to relevant regulations, chlorothalonil residues are defined as the sum of chlorothalonil and its metabolite 4-hydroxychlorothalonil; therefore, an analytical method for simultaneously detecting both is needed.

[0004] Currently, common detection methods for chlorothalonil and 4-hydroxychlorothalonil include gas chromatography, gas chromatography-mass spectrometry, and atmospheric pressure chemical ionization source-tandem mass spectrometry. Because chlorothalonil is prone to hydrolysis under alkaline conditions (generally pH > 9), existing methods often employ neutral or acidic extraction systems to inhibit its transformation. Although several residue detection methods have achieved good results in matrices such as cucumber and cherry tomato, for complex matrices rich in sulfur, such as leeks, onions, garlic, garlic scapes, and white radishes, naturally occurring sulfur derivatives can bind with chlorothalonil, leading to unacceptable recovery rates. This can result in severely underestimated residue levels or even false negative results, a problem that has long plagued researchers in related fields.

[0005] In existing technologies, for example, Chinese invention patent application CN114354823A discloses a method for detecting chlorothalonil and its metabolites in agricultural products. It indicates that chlorothalonil can be rapidly converted into thiol-based chlorothalonil in matrices such as radish and onion, with a conversion rate of 10%–100%. The method also attempts to inhibit the conversion under acidic conditions and uses gas chromatography-tandem triple quadrupole mass spectrometry (GC-MS) to quantify the chlorothalonil technical. However, this method still has the following limitations: even under acidic conditions, it is difficult to completely avoid the degradation and transformation of chlorothalonil during the detection process; to comprehensively assess the residue situation, liquid chromatography-tandem mass spectrometry (LC-MS) is required to detect metabolites and transformation products, resulting in the need for at least two sets of large-scale instruments, leading to high costs; furthermore, during the sample preparation stage, the sulfur derivative groups released instantaneously upon plant cell rupture react with chlorothalonil, and this transformation is difficult to avoid. Existing technologies do not adequately cover this process, therefore, they cannot accurately reflect the actual residue level of chlorothalonil in the sample.

[0006] In summary, existing methods for detecting chlorothalonil and its metabolites and transformation products in sulfur-containing complex matrices suffer from several drawbacks, including difficulty in inhibiting transformation during pretreatment, high costs due to the need for multiple instruments, cumbersome operation, and an inability to accurately reflect the initial total residue. Therefore, developing a matrix-compatible, simple, rapid, and low-cost method for the simultaneous and accurate quantification of chlorothalonil and its metabolites and derivatives has become a pressing technical challenge in this field. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a method for determining the amount of chlorothalonil residue in fruits and vegetables. It abandons the traditional approach of inhibiting transformation and instead adopts a strategy of promoting complete transformation and indirectly determining the total amount, effectively solving the problems of low recovery rate and false negatives in the detection of chlorothalonil in complex matrices.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for determining the residue of chlorothalonil in fruits and vegetables includes the following steps: S1. Extraction: The fruit and vegetable samples were extracted using an alkaline extraction solution to obtain the extract. S2, Conversion: Add allicin solution to the extract obtained in step S1 to fully convert chlorothalonil in the sample into its derivative mercaptochlorothalonil, and obtain the conversion solution; S3. Purification: Add purification packing to the conversion solution obtained in step S2, and after vortexing, centrifugation and filtration, obtain the test solution; S4. Detection and Calculation: The concentrations of thiophanate-methyl and 4-hydroxychlorothalonil in the test solution obtained in step S3 were detected using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS / MS), and the total residual amount of chlorothalonil in the sample was calculated based on the following formula:

[0009] Among them, C 巯基百菌清 and C 4-羟基百菌清 The concentrations of thiophanate-methyl and 4-hydroxychlorothalonil in the test solution are shown in μg / L, respectively; C 百菌清 The value of chlorothalonil in the calculated sample is expressed in μg / kg; V is the volume of extract added in mL; m is the mass of the sample weighed in g; and 1000 is the unit conversion factor.

[0010] Based on the above technical solution, the present invention can also be improved as follows: Further, in step S1, the alkaline extract is an organic solvent containing 0.1% to 0.2% (volume fraction) ammonia water, and the organic solvent is selected from acetonitrile, methanol, acetonitrile-water mixed solvent, and methanol-water mixed solvent; in step S1, 2 mL to 4 mL of alkaline extract is added per gram of sample.

[0011] Studies have shown that chlorothalonil reacts with HS under alkaline conditions. - A nucleophilic aromatic substitution reaction occurs, which can efficiently convert the fungicide into thiophanate-methyl, and the stronger the alkalinity, the faster the reaction rate. This invention uses water containing 0.1% to 0.2% ammonia as an alkaline extract, providing a favorable alkaline environment for the release of H2S and the nucleophilic substitution reaction; the added allicin acts as an H2S donor, ensuring an ample supply of H2S.

[0012] A weakly alkaline environment is conducive to the stable extraction of the target analyte and lays the foundation for subsequent transformation steps.

[0013] Furthermore, in step S2, the allicin solution is a methanol solution containing 0.01 g / mL to 0.05 g / mL allicin; in step S2, the amount of allicin solution added is 0.5 mL per mL of extract.

[0014] Conventional methods use various acids to inhibit the conversion of chlorothalonil, but this invention takes the opposite approach, using an alkaline extraction solution. In the presence of allicin, chlorothalonil in the sample is converted to thiochlorothalonil. The principle is that the main active components of allicin are diallyl trisulfide (DATS) and diallyl disulfide (DADS), both of which are H2S donors. Chlorothalonil reacts with H2S / HS... - The reaction produces thiol-based chlorothalonil.

[0015] When the allicin content of the allicin solution is in the range of 0.01 g / mL to 0.05 g / mL, and the added volume is 0.5 mL per mL of extract, the conversion rate of chlorothalonil in most matrices is above 99.5%. Allicin, as a conversion agent, ensures that residual chlorothalonil in different fruit and vegetable matrices (especially low-sulfur matrices) can be efficiently and quantitatively converted into mercaptochlorothalonil, thus solving the systematic error caused by inconsistent conversion rates. When the allicin content of the allicin solution exceeds 0.05 g / mL, it does not contribute to improving the conversion rate; instead, it increases additional costs and may cause instrument contamination.

[0016] Furthermore, in step S3, the purification packing is an enhanced lipid removal adsorbent (EMR adsorbent), which can selectively adsorb non-polar interfering substances such as lipids and pigments in the sample matrix, significantly reducing the matrix effect and improving the sensitivity and accuracy of the method.

[0017] Furthermore, in step S3, the enhanced lipid removal adsorbent has a mesh size of 200-400 mesh; the purification packing is added at a rate of 100-500 mg per mL of conversion solution.

[0018] Furthermore, in step S4, the detection conditions of the ultra-high performance liquid chromatography-tandem mass spectrometry are as follows: electrospray ionization negative ion mode is used; the chromatographic column is a high-strength silica-bonded C24 column. 18 Chromatographic column; mobile phase A is acetonitrile, mobile phase B is water; gradient elution program is used.

[0019] Furthermore, in step S4, the detection conditions for the ultra-high performance liquid chromatography-tandem mass spectrometry are: capillary voltage of -500V to -2500V, desolvation gas of nitrogen, desolvation gas temperature of 400℃ to 500℃, and desolvation gas flow rate of 13L / min to 16L / min.

[0020] Furthermore, in step S4, a gradient elution program is adopted. Specifically, the gradient elution program is as follows: 0 min to 0.5 min, 20% A; 0.5 min to 3.0 min, 20% A → 90% A; 3.0 min to 4.5 min, 90% A; 4.5 min to 5.0 min, 90% A → 20% A; 5.0 min to 6.0 min, 20% A.

[0021] Furthermore, the quantification of thiophanate-methyl and 4-hydroxychlorothalonil was performed using the standard curve method. The method for preparing the standard curve was as follows: a mixed standard working solution of chlorothalonil and 4-hydroxychlorothalonil was sampled and mixed according to different concentrations, a methanol solution containing allicin was added, the mixture was vortexed, filtered, and detected by ultra-high performance liquid chromatography-tandem mass spectrometry. Standard curves for thiophanate-methyl and 4-hydroxychlorothalonil were plotted based on the concentration and response area, respectively. The concentration and response area values ​​showed a linear relationship.

[0022] Furthermore, the concentrations of chlorothalonil and 4-hydroxychlorothalonil in the mixed standard working solution were 1.0 μg / L, 5.0 μg / L, 10.0 μg / L, 20.0 μg / L, and 40.0 μg / L, respectively. 1 mL of the mixed standard working solution was taken and 0.5 mL of methanol solution containing 0.01 g / mL allicin was added.

[0023] Furthermore, the vortex oscillation speed is 2000 r / min to 3000 r / min, and the time is 8 min to 15 min.

[0024] Furthermore, the centrifugal filtration uses an injection needle filter, with a centrifugation speed of 10000 r / min to 15000 r / min and a centrifugation time of 3 min to 5 min.

[0025] Furthermore, the filter membrane material of the injection needle filter is selected from any one of polyethersulfone resin, nylon 66, polytetrafluoroethylene, and polyvinylidene fluoride; the pore size of the filter membrane is 0.20μm to 0.25μm.

[0026] Furthermore, the fruit and vegetable samples are selected from at least one of the following: spinach, green bell pepper, strawberry, cabbage, tomato, carrot, cauliflower, cucumber, blueberry, potato, pumpkin, burdock, oyster mushroom, apple, green bean, bok choy, yam, corn, Chinese cabbage, peach, cantaloupe, sweet pea, lettuce, watermelon, taro, scallion, chive, onion, leek, garlic, garlic scape, and white radish.

[0027] The beneficial effects of this invention are as follows: This invention breaks through the traditional approach of inhibiting chlorothalonil conversion. By using alkaline extraction and exogenous allicin catalysis, it actively promotes the complete and quantitative conversion of chlorothalonil into a single derivative, transforming the complex and uncontrollable conversion process into a controllable and quantitative chemical reaction. In principle, this avoids the problems of low recovery rate and false negatives caused by incomplete or unmeasurable conversion.

[0028] This invention, by simultaneously measuring the conversion product (thiol chlorothalonil) and the natural metabolite (4-hydroxychlorothalonil) and using the conversion coefficient, can accurately reflect the total residual level of chlorothalonil (technical drug, metabolites, and matrix conjugates) in a sample, meeting regulatory requirements.

[0029] This invention specifically addresses the industry challenge of detecting sulfur-containing complex matrices such as leeks, onions, and garlic, providing a stable and reliable solution with significantly improved recovery rates and stable results.

[0030] This invention introduces exogenous allicin, making the method highly applicable to all fruit and vegetable matrices (regardless of sulfur content). The method requires only one ultra-high performance liquid chromatography-tandem mass spectrometer, and the entire detection process is completed within 12 hours. It is simple, possesses excellent accuracy, precision, and robustness.

[0031] This invention reduces the use of expensive equipment, simplifies the pretreatment steps, and consumes less reagent, making it an economical, efficient, and green detection method. Attached Figure Description

[0032] Figure 1 The standard curve for 4-hydroxychlorothalonil; Figure 2 The standard curve for thiophanate-methyl; Figure 3 The UHPLC-MS / MS chromatogram of thiophanate-methyl in potato matrix without added allicin; Figure 4 The UHPLC-MS / MS chromatogram of thiophanate-methyl in a potato matrix with added allicin. Detailed Implementation

[0033] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0034] Example 1 Determination of chlorothalonil in onions Sample preparation: Take negative onion samples, homogenize and grind them evenly, add chlorothalonil standard at three levels of 3 μg / kg, 5 μg / kg and 10 μg / kg respectively, and store at -18℃.

[0035] The simulated spiked onions were used as samples to determine their chlorothalonil concentration, specifically including the following steps: (1) Extraction: Weigh 5.0g of the above sample, 7 parallel samples for each level, add 10.0mL of methanol solution containing 0.1% ammonia water, vortex at 2500r / min for 5min, centrifuge at 4000r / min for 5min, and take the supernatant.

[0036] (2) Conversion: Take 10 mL of supernatant, add 5 mL of methanol solution containing 0.01 g / mL allicin, vortex at 2500 r / min for 10 min, centrifuge at 4000 r / min for 5 min, and take the supernatant.

[0037] (3) Purification: Take 1 mL of conversion solution, add 100 mg of EMR adsorbent (300 mesh), vortex at 2500 r / min for 2 min, centrifuge at 10000 r / min for 1 min, and filter through a syringe filter (0.22 μm polytetrafluoroethylene filter membrane) to obtain the test solution.

[0038] (4) Preparation of standard curves: Prepare mixed standard working solutions of chlorothalonil and 4-hydroxychlorothalonil, with concentrations of 1.0 μg / L, 5.0 μg / L, 10.0 μg / L, 20.0 μg / L, and 40.0 μg / L. Take 1 mL of each concentration standard solution, add 0.5 mL of methanol solution containing 0.01 g / mL allicin, vortex for 10 minutes, and perform the same purification treatment as in step (3). Use ultra-high performance liquid chromatography-tandem mass spectrometry to detect the concentration and peak area, respectively, and plot the standard curves of 4-hydroxychlorothalonil and mercaptochlorothalonil (see [link to relevant documentation]). Figure 1 and Figure 2 ).

[0039] (5) Quantitative detection and calculation: UHPLC-MS / MS was used for detection, with the electrospray ionization source in negative mode. The capillary voltage was -2500V, the desolventizing gas was nitrogen, the desolventizing gas temperature was 500℃, and the desolventizing gas flow rate was 16L / min. The chromatographic column was a high-strength silica-bonded C16 column. 18 Column (2.7 µm, 2.1 × 100 mm); mobile phase: A is acetonitrile, B is water; gradient elution, program as shown in Table 1 below; flow rate 0.5 mL / min.

[0040] Table 1 Gradient elution program

[0041] (6) Calculation and statistics of results: The concentrations C of 4-hydroxychlorothalonil and mercaptochlorothalonil were obtained according to the standard curves of 4-hydroxychlorothalonil and mercaptochlorothalonil, respectively. 巯基百菌清 and C 4-羟基百菌清 Calculate the chlorothalonil content C using the following formula. 百菌清 .

[0042]

[0043] Among them, C 巯基百菌清 and C 4-羟基百菌清 The concentrations of thiophanate-methyl and 4-hydroxychlorothalonil in the test solution are shown in μg / L, respectively; C 百菌清 The value of chlorothalonil in the calculated sample is expressed in μg / kg; V is the volume of extract added in mL; m is the mass of the sample weighed in g; and 1000 is the unit conversion factor.

[0044] In the above formula, coefficient 1.009 is the conversion coefficient for thiol chlorothalonil to chlorothalonil, and its theoretical value is calculated based on the molecular weight of both. Coefficient 1.075 is the equivalent coefficient for 4-hydroxychlorothalonil to chlorothalonil, which is determined based on the molecular weight of both and is used to convert the detected metabolite content into an equivalent amount of chlorothalonil content.

[0045] Results: The recovery rate of onion samples ranged from 91.8% to 105.9%, and the relative standard deviation of parallel samples was less than or equal to 4.7%.

[0046] Example 2 Determination of chlorothalonil in chives The steps were basically the same as in Example 1, except that: the sample was spiked chives, weighed 10.0 g, the alkaline extract volume was 20.0 mL, and the allicin solution was a methanol solution containing 0.02 g / mL allicin. In the UHPLC-MS / MS detection parameters, the desolvation gas temperature was 450℃, and the flow rate was 13 L / min.

[0047] Results: The recovery rate of chive samples ranged from 92.5% to 105.8%, and the relative standard deviation of parallel samples was less than or equal to 5.1%.

[0048] Example 3 Determination of chlorothalonil in potatoes The steps are basically the same as in Example 1, except that: the sample is spiked potato, the alkaline extract volume is 20.0 mL, the conversion sampling volume is 20 mL, and the allicin solution is a methanol solution containing 0.05 g / mL allicin. In the UHPLC-MS / MS detection parameters, the capillary voltage is -500 V, the desolvation gas temperature is 400℃, and the flow rate is 15 L / min. The chromatogram of thiophanate-methyl in the potato sample of this example can be found in [reference needed]. Figure 4 The quantitative ion pair for thiophanate-methyl monitored in multiple reaction mode was 261 > 225.8, and the qualitative ion pair was 261 > 190.9.

[0049] Results: The recovery rate of potato samples ranged from 91.5% to 106.5%, and the relative standard deviation of parallel samples was less than or equal to 6.6%.

[0050] This embodiment includes a control group, in which no allicin methanol solution was added. The presence of thiophanate-methyl in potato samples from the control group was detected by UHPLC-MS / MS. The chromatogram is shown below. Figure 3 .

[0051] from Figure 3 and Figure 4It is evident that the control group without allicin contained more matrix impurities and denser impurity peaks, lacking the characteristic peak of thiochlorothiazide (which corresponds to a short peak). In contrast, the addition of allicin methanol solution in this embodiment effectively promoted the conversion of chlorothalonil, and a sharp characteristic peak of thiochlorothiazide appeared in the chromatogram. This demonstrates that under the detection conditions of this invention, allicin can stably achieve the conversion of chlorothalonil to thiochlorothiazide, fully meeting the accuracy requirements for quantitative detection.

[0052] The recovery rates of chlorothalonil simulated addition in Examples 1-3 are shown in Table 2.

[0053] Table 2. Recovery rates of chlorothalonil under simulated additives in each example

[0054] The data in Table 2 clearly demonstrate that the method proposed in this invention exhibits high accuracy and precision in practical applications with both sulfur-containing matrices (such as sulfur-rich samples like onions and leeks) and non-sulfur matrices (such as samples like potatoes that contain no sulfur or have extremely low sulfur content), demonstrating excellent applicability and adaptability to the detection needs of different types of samples. Whether facing complex interference from sulfur-containing components or processing relatively simple non-sulfur matrix samples, this invention can stably and reliably complete the determination of total chlorothalonil residues, fully demonstrating its high efficiency and wide applicability in practical operation.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the residue of chlorothalonil in fruits and vegetables, characterized in that, Includes the following steps: S1. Extraction: The sample is homogenized and pulverized evenly. The fruit and vegetable sample is extracted with an alkaline extractant to obtain an extractant. The alkaline extractant is a methanol solution containing 0.1% ammonia. S2, Conversion: Add allicin solution to the extract obtained in step S1 to obtain the conversion solution; S3. Purification: Add purification packing to the conversion solution obtained in step S2, and after vortexing, centrifugation and filtration, obtain the test solution; S4. Detection and Calculation: Using ultra-high performance liquid chromatography-tandem mass spectrometry, the concentrations of thiophanate-methyl and 4-hydroxychlorothalonil in the test solution obtained in step S3 were detected, and the total residual amount of chlorothalonil in the sample was calculated based on the following formula: Among them, C 巯基百菌清 and C 4-羟基百菌清 The concentrations of thiophanate-methyl and 4-hydroxychlorothalonil in the test solution are respectively; C 百菌清 V is the volume of chlorothalonil added to the sample; m is the mass of the sample weighed; and 1000 is the unit conversion factor. Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS / MS) was used for detection with a negative mode electrospray ionization source at a capillary voltage of -2500V. Nitrogen was used as the desolventizing gas at a temperature of 500℃ and a flow rate of 16 L / min. The chromatographic column was a high-strength silica-bonded C24 column. 18 Column: 2.7 µm, 2.1 × 100 mm; Mobile phase: A is acetonitrile, B is water; Gradient elution program: 0 min–0.5 min, 20% A; 0.5 min–3.0 min, 20% A → 90% A; 3.0 min–4.5 min, 90% A; 4.5 min–5.0 min, 90% A → 20% A; 5.0 min–6.0 min, 20% A; Flow rate: 0.5 mL / min.

2. The method for determining the residue of chlorothalonil in fruits and vegetables according to claim 1, characterized in that, In step S1, 2 mL to 4 mL of alkaline extract is added per gram of sample.

3. The method for determining the residue of chlorothalonil in fruits and vegetables according to claim 1, characterized in that, In step S2, the allicin solution is a methanol solution containing 0.01 g / mL to 0.05 g / mL allicin; in step S2, the amount of allicin solution added is 0.5 mL per mL of extract.

4. The method for determining the residue of chlorothalonil in fruits and vegetables according to claim 1, characterized in that, In step S3, the purification packing is an enhanced lipid removal adsorbent with a mesh size of 200-400 mesh; the amount of purification packing added is 100-500 mg per mL of conversion solution.

5. The method for determining the residue of chlorothalonil in fruits and vegetables according to claim 1, characterized in that, In step S4, the quantification of thiophanate-methyl and 4-hydroxychlorothalonil was performed using the standard curve method. The method for preparing the standard curve was as follows: mixed standard working solutions of chlorothalonil and 4-hydroxychlorothalonil were prepared according to different concentrations, samples were taken, methanol solution containing allicin was added, the mixture was vortexed, centrifuged and filtered, and detected by ultra-high performance liquid chromatography-tandem mass spectrometry. Standard curves for thiophanate-methyl and 4-hydroxychlorothalonil were plotted based on the concentration and response area, and the concentration and response area values ​​showed a linear relationship.

6. The method for determining the residue of chlorothalonil in fruits and vegetables according to claim 5, characterized in that, The concentrations of chlorothalonil and 4-hydroxychlorothalonil in the mixed standard working solution were 1.0 μg / L, 5.0 μg / L, 10.0 μg / L, 20.0 μg / L, and 40.0 μg / L, respectively. 1 mL of the mixed standard working solution was taken and 0.5 mL of methanol solution containing 0.01 g / mL allicin was added.

7. The method for determining the residue of chlorothalonil in fruits and vegetables according to claim 5, characterized in that, The vortex oscillation speed is 2000 r / min to 3000 r / min, and the time is 8 min to 15 min; Centrifugal filtration uses an injection needle filter, with a centrifugation speed of 10000 r / min to 15000 r / min and a centrifugation time of 3 min to 5 min.

8. The method for determining the residue of chlorothalonil in fruits and vegetables according to claim 7, characterized in that, The filter membrane material of the injection needle filter is selected from any one of polyethersulfone resin, nylon 66, polytetrafluoroethylene, and polyvinylidene fluoride; the pore size of the filter membrane is 0.20μm to 0.25μm.

9. The method for determining the residue of chlorothalonil in fruits and vegetables according to any one of claims 1 to 8, characterized in that, The fruit and vegetable samples were selected from at least one of the following: spinach, green bell pepper, strawberry, cabbage, tomato, carrot, cauliflower, cucumber, blueberry, potato, pumpkin, burdock, oyster mushroom, apple, green bean, bok choy, yam, corn, Chinese cabbage, peach, cantaloupe, sweet pea, lettuce, watermelon, taro, scallion, chive, onion, leek, garlic, garlic scape, and white radish.

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