Corn pesticide residue detection method

Abstract

The invention discloses a corn pesticide residue detection method, and belongs to the technical field of food quality safety detection.The method comprises the steps that a to-be-detected corn sample is obtained through quartering sampling, smashing and sample weighing, acetonitrile and ultrapure water are added into the to-be-detected corn sample, an organic phase is obtained through layering treatment, the organic phase is concentrated and purified, a to-be-detected solution is obtained, and the to-be-detected solution is detected. The method comprises the following steps: detecting a liquid to be detected by using a gas chromatograph equipped with different detectors to obtain pesticide chromatogram data, preparing a series of concentration standard solutions of organophosphorus and organochlorine pesticides, detecting, drawing a peak area concentration standard curve, extracting a peak area from the pesticide chromatogram data, and substituting the peak area into the standard curve to calculate the pesticide residue concentration. And carrying out re-detection judgment in combination with a pesticide residue quantitative threshold value. The method can accurately detect organophosphorus pesticide residues and organochlorine pesticide residues in corn, and meets actual detection requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of food quality and safety detection, and particularly relates to a method for detecting pesticide residues in corn. Background Art

[0002] As an important food, feed, and industrial raw material, various pesticides including insecticides, herbicides, fungicides, and acaricides are often used in the planting process of corn due to the need for pest control. If pesticide residues enter the human body through the food chain, they will pose a potential threat to health. Therefore, it is crucial to establish an accurate and efficient method for detecting pesticide residues in corn.

[0003] Currently, the methods for detecting pesticide residues in feed and agricultural products mainly rely on national standards for detection, but there are significant deficiencies, including: the need for high-temperature burning of anhydrous sodium sulfate and activated carbon, or the use of complex purification means such as gel permeation chromatography and self-packed chromatography columns, which are complex and cumbersome and not suitable for batch detection; involving a variety of toxic and harmful reagents, posing risks to the health of operators and the environment, and relying on highly professional instruments and operating skills, which limit the popularization of the method; existing national standards mostly target single categories of pesticides, lacking an efficient method for simultaneously detecting multiple categories of pesticides. Therefore, for the detection of pesticide residues in corn, there is an urgent need for a method with simple pretreatment, wide detection range, high accuracy, and strong safety to solve the problems of complex operation, low efficiency, and insufficient multi-residue detection ability in the existing technology. For this reason, a method for detecting pesticide residues in corn is now proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for detecting pesticide residues in corn to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for detecting pesticide residues in corn, comprising the following steps:

[0007] S1. Sampling the corn by the quartering method to obtain a corn sample, and performing crushing and weighing on the corn sample to obtain a corn sample to be detected;

[0008] S2. Adding the corn sample to be detected to acetonitrile and ultrapure water, and performing stratification treatment to obtain an organic phase, and performing concentration and purification treatment on the organic phase to obtain a liquid to be detected for organophosphorus pesticides and a liquid to be detected for organochlorine pesticides;

[0009] S3. Detecting the liquid to be detected for organophosphorus pesticides and the liquid to be detected for organochlorine pesticides respectively by a gas chromatograph to obtain pesticide chromatogram data;

[0010] S4. Take the organophosphorus pesticide standard solution and the organochlorine pesticide standard solution, prepare a series of concentration standard solutions for the organophosphorus pesticide standard solution and the organochlorine pesticide standard solution respectively, and detect the series of concentration standard solutions by a gas chromatograph to obtain the chromatogram data of the pesticide standard concentration. According to the chromatogram data of the pesticide standard concentration, draw the peak area concentration standard curve;

[0011] S5. Extract the peak area from the pesticide chromatogram data, calculate the peak area through the peak area concentration standard curve to obtain the pesticide residue concentration. At the same time, construct a quantitative threshold for pesticide residues, compare the pesticide residue concentration with the quantitative threshold for pesticide residues, and conduct a re-inspection judgment.

[0012] Preferably, the method for obtaining the corn sample to be tested:

[0013] Take samples from the corn by the quartering method to obtain corn samples. Break the corn samples into a uniform paste by a blender, and weigh the corn samples after being broken by an electronic balance to accurately weigh 25.0 g of the corn sample to be tested;

[0014] The quartering method is a method used to reduce the sample amount and ensure the representativeness of the sample.

[0015] Preferably, the method for obtaining the organophosphorus pesticide solution to be detected:

[0016] Add 50 mL of acetonitrile and 30 mL of ultrapure water to the corn sample to be tested, and place it in a homogenizer for homogenization extraction for 2 min. Put the corn sample to be tested after homogenization extraction into a 100 mL stoppered graduated cylinder containing 15.0 g of sodium chloride, shake it vigorously for 30 s, and then let it stand at room temperature for 30 min to completely separate the organic phase and the aqueous phase, and obtain the organic phase and the aqueous phase;

[0017] Extract 10 mL of the organic phase through a pipette to obtain 10 mL of the organic phase to be tested. Place the 10 mL of the organic phase to be tested on an 80 °C water bath and heat it. At the same time, pass nitrogen through a nitrogen blower to blow it to nearly dry, and add 5 mL of acetone to make up the volume to 5 mL. Vortex-mix the organic phase to be tested after acetone volume making for 30 s to obtain a pesticide-acetone mixture. Filter the pesticide-acetone mixture through a 0.22 μm organic filter membrane to obtain the organophosphorus pesticide solution to be detected;

[0018] The homogenization extraction is a technical means applied in sample processing;

[0019] The vortex mixing is a mixing technique applied in the field of chemical analysis.

[0020] Preferably, the method for obtaining the organochlorine pesticide solution to be detected:

[0021] Add 50 mL of acetonitrile and 25 mL of ultrapure water to the corn sample to be tested, place it in a homogenizer for homogenization extraction for 2 min, put the homogenized corn sample to be tested into a 100 mL stoppered graduated cylinder containing 15.0 g of sodium chloride, shake vigorously for 30 s, and then let it stand at room temperature for 30 min to completely separate the organic phase and the aqueous phase, obtaining the organic phase and the aqueous phase;

[0022] Extract 10 mL of the organic phase with a pipette to obtain 10 mL of the organic phase to be tested. Place the 10 mL of the organic phase to be tested on an 80 °C water bath for heating. At the same time, pass nitrogen through a nitrogen blower to blow it to near dryness. Add 2 mL of n-hexane to the nearly dry organic phase to be tested, and vortex mix it for 30 s with a vortex mixer to obtain the solution to be purified;

[0023] Pre-rinse the Florisil solid phase extraction column successively with 5 mL of a mixed solution of acetone and n-hexane with a ratio of acetone to n-hexane of 1:9 and 5 mL of n-hexane. When the liquid level in the Florisil solid phase extraction column reaches the surface of the adsorption layer of the Florisil solid phase extraction column, immediately pour in the solution to be purified, and collect the eluate with a centrifuge tube. Heat the eluate to 50 °C. At the same time, pass nitrogen through a nitrogen blower to blow it to near dryness. Add n-hexane to the nearly dry eluate to make the volume constant to 5 mL, and vortex mix it for 30 s with a vortex mixer to obtain a mixed solution of pesticides and n-hexane. Filter the mixed solution of pesticides and n-hexane through a 0.22 μm organic filter membrane to obtain the solution to be detected for organochlorine pesticides.

[0024] Preferably, the method for detecting the solution to be detected for organophosphorus pesticides by a gas chromatograph:

[0025] Select a gas chromatograph equipped with a flame photometric detector, split injection, an RTX-5 and a wondacap-17 capillary column. Set the column temperature program of the gas chromatograph, with the carrier gas flow rate of 9 mL / min, the injection volume of 1 μL, the temperature of the flame photometric detector of 270 °C, the injection port temperature of 220 °C, the air flow rate of 90 mL / min, and the split ratio of 3:1. Inject the solution to be detected for organophosphorus pesticides into the set gas chromatograph to obtain pesticide chromatogram data;

[0026] The column temperature program is that the initial column temperature is 150 °C and is maintained for 2 min, and then it is raised to the column temperature of 250 °C at a rate of 8 °C / min and maintained for 18 min.

[0027] Preferably, the method for monitoring the solution to be detected for organochlorine pesticides by a gas chromatograph:

[0028] Select a gas chromatograph equipped with an electron capture detector, an RTX-5 capillary column, and a Wondacap-1 capillary column. Set the column temperature program of the gas chromatograph, the injection volume to 1 μL, the electron capture detector temperature to 320 °C, the injection port temperature to 200 °C, the gas flow rate to 14 mL / min, and the split ratio to 10:1. Inject the organic chlorine pesticide liquid to be detected into the set gas chromatograph to obtain pesticide chromatogram data;

[0029] The column temperature program is that the initial column temperature is maintained at 150 °C for 2 min, and then increased to 270 °C at a rate of 6 °C / min and maintained for 18 min.

[0030] Preferably, a method for preparing series concentration standard solutions for organophosphorus pesticide standard solutions and organochlorine pesticide standard solutions respectively and detecting the series concentration standard solutions by a gas chromatograph:

[0031] Take 100 μL of 1000 mg / L organophosphorus pesticide standard solution, add acetone to the organophosphorus pesticide standard solution to prepare five 10 mL series concentration standard solutions with organophosphorus pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L, and 0.4 mg / L. Use the method of detecting the organophosphorus pesticide liquid to be detected by a gas chromatograph for the five 10 mL series concentration standard solutions with organophosphorus pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L, and 0.4 mg / L to obtain pesticide standard concentration chromatogram data;

[0032] Take 100 μL of 1000 mg / L organochlorine pesticide standard solution, add n-hexane to the organochlorine pesticide standard solution to prepare five 10 mL series concentration standard solutions with organochlorine pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L, and 0.4 mg / L. Use the method of detecting the organochlorine pesticide liquid to be detected by a gas chromatograph for the five 10 mL series concentration standard solutions with organochlorine pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L, and 0.4 mg / L to obtain pesticide standard concentration chromatogram data;

[0033] The organophosphorus pesticide standard solution is a solution with the concentrations of ethoprophos, monocrotophos, malathion, fenthion, isocarbophos, and profenofos all being 1000 mg / L. Among them, the organophosphorus pesticides include the concentrations of ethoprophos, monocrotophos, malathion, fenthion, isocarbophos, and profenofos;

[0034] The organochlorine pesticide standard solution is a solution with the concentrations of metolachlor, fenvalerate, deltamethrin, cyhalothrin, procymidone and chlorfenapyr all being 1000 mg / L. Among them, the organochlorine pesticides include fungicides, herbicides, insecticides and acaricides, and metolachlor, fenvalerate, deltamethrin, cyhalothrin, procymidone and chlorfenapyr are the main components of the organochlorine pesticides.

[0035] Preferably, according to the chromatogram data of the pesticide standard concentration, the method for drawing the peak area concentration standard curve is as follows:

[0036] Extract the peak area and the retention time corresponding to the peak area from the chromatogram data of the pesticide standard concentration. Determine the pesticide type corresponding to the peak area according to the retention time corresponding to the peak area, and manually mark the standard solution concentration and pesticide type corresponding to the peak area. Using the standard solution concentration X mg / kg as the abscissa and the peak area Y as the ordinate, perform least squares linear regression through the chromatographic workstation software to obtain the peak area concentration standard curve of each pesticide type;

[0037] The retention time corresponding to the peak area is the peak emergence time;

[0038] The peak area concentration standard curves of each pesticide type are respectively:

[0039] The peak area concentration standard curve of ethoprophos is: Y = 2.84152×10 6 X; the peak area concentration standard curve of monocrotophos is: Y = 1.24176×10 6 X; the peak area concentration standard curve of malathion is: Y = 2.02256×10 6 X; the peak area concentration standard curve of fenthion is: Y = 2.69068×10 6 X; the peak area concentration standard curve of isocarbophos is: Y = 2.31762×10 6 X; the peak area concentration standard curve of profenofos is: Y = 1.46016×10 6 X; the peak area concentration standard curve of metolachlor is: Y = 1.06066×10 6 X; the peak area concentration standard curves of fenvalerate are: Y = 489356X and Y = 330041X; the peak area concentration standard curves of deltamethrin are: Y = 376003X and Y = 262461X; the peak area concentration standard curves of cyhalothrin are: Y = 140343X and Y = 765769X; the peak area concentration standard curve of procymidone is: Y = 828962X; the peak area concentration standard curve of chlorfenapyr is: Y = 809370X;

[0040] Among them, X is the pesticide residue concentration and Y is the peak area;

[0041] The types of pesticides include ethoprophos, monocrotophos, malathion, fenthion, isocarbophos, profenofos, metolachlor, fenvalerate, deltamethrin, cyhalothrin, procymidone, and chlorfenapyr;

[0042] The chromatographic workstation software is a professional software for controlling the operation of chromatographic instruments, collecting, and processing chromatographic data;

[0043] The least squares linear regression is a statistical method for fitting data by minimizing the sum of the squares of the errors.

[0044] Preferably, the method for obtaining the pesticide residue concentration:

[0045] Extract the peak area and the retention time corresponding to the peak area from the pesticide concentration chromatogram data. According to the retention time corresponding to the peak area, determine the type of pesticide corresponding to the peak area, and substitute the peak area into the peak area concentration standard curve of the corresponding pesticide type for calculation to obtain the pesticide residue concentration. When the corresponding pesticide types are fenvalerate, deltamethrin, and cyhalothrin, there are two peak area concentration standard curves for fenvalerate, deltamethrin, and cyhalothrin. Determine the peak area concentration standard curves for fenvalerate, deltamethrin, and cyhalothrin through the retention time corresponding to the peak area to obtain the pesticide residue concentration;

[0046] Determine the type of pesticide corresponding to the peak area according to the retention time corresponding to the peak area, where the relationship between the retention time corresponding to the peak area is as follows: if the retention time corresponding to the peak area is 13.893 min, the corresponding pesticide type is S-metolachlor; if the retention time corresponding to the peak area is 15.617 min, the corresponding pesticide type is procymidone; if the retention time corresponding to the peak area is 17.723 min, the corresponding pesticide type is chlorfenapyr; if the retention time corresponding to the peak area is 22.203 min and 22.545 min, the corresponding pesticide type is lambda-cyhalothrin. Among them, when the retention time corresponding to the peak area is 22.203 min, the standard curve of the peak area concentration of lambda-cyhalothrin is Y = 140343X; when the retention time corresponding to the peak area is 22.545 min, the standard curve of the peak area concentration of lambda-cyhalothrin is Y = 262461X; if the retention time corresponding to the peak area is 29.037 min and 29.779 min, the corresponding pesticide type is fenvalerate. Among them, when the retention time corresponding to the peak area is 29.037 min, the standard curve of the peak area concentration of fenvalerate is Y = 489356X; when the retention time corresponding to the peak area is 22.545 min, the standard curve of the peak area concentration of fenvalerate is Y = 330041X; if the retention time corresponding to the peak area is 31.108 min and 32.007 min, the corresponding pesticide type is deltamethrin. Among them, when the retention time corresponding to the peak area is 31.108 min, the standard curve of the peak area concentration of deltamethrin is Y = 376003X; when the retention time corresponding to the peak area is 32.007 min, the standard curve of the peak area concentration of deltamethrin is Y = 262461X;

[0047] If the retention time corresponding to the peak area is 6.433 min, the corresponding pesticide type is ethoprophos; if the retention time corresponding to the peak area is 7.057 min, the corresponding pesticide type is monocrotophos; if the retention time corresponding to the peak area is 10.468 min, the corresponding pesticide type is malathion; if the retention time corresponding to the peak area is 10.713 min, the corresponding pesticide type is fenthion; if the retention time corresponding to the peak area is 10.941 min, the corresponding pesticide type is isocarbophos; if the retention time corresponding to the peak area is 12.898 min, the corresponding pesticide type is profenofos;

[0048] Preferably, a method for constructing a quantitative threshold for pesticide residues and comparing the pesticide residue concentration with the quantitative threshold for pesticide residues for re-inspection judgment:

[0049] If the pesticide residue concentration is greater than or equal to the quantitative threshold for pesticide residues of 0.02 mg / kg, the pesticide residue concentration is obtained;

[0050] If the pesticide residue concentration is less than the pesticide residue quantification threshold of 0.02 mg / kg, it indicates that the operation of corn pesticide residue detection is not standardized, and the corn pesticide residue detection should be carried out again.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. The present invention realizes simple, efficient and significantly reduced operation cost in sample pretreatment. The method adopts acetonitrile extraction combined with differential purification technology, namely membrane filtration and Florisil solid phase extraction column, without complex steps such as high-temperature calcination and gel purification, avoiding cumbersome operations, significantly shortening the sample treatment time and improving the detection efficiency. At the same time, it reduces the use of highly toxic reagents, reduces the operation risk and environmental burden, and is suitable for rapid detection of a large number of samples.

[0053] 2. The present invention can simultaneously detect multiple types of pesticides with a wide coverage range and accurate quantification. This method innovatively realizes the simultaneous detection of 6 kinds of organophosphorus pesticides and 6 kinds of organochlorine pesticides, solving the limitation of single-category detection in the existing national standards. By optimizing the gas chromatography conditions and the standard curve drawing method, it ensures the accurate identification and quantification of multiple residues in complex matrices, filling the technical gap in the simultaneous detection of multiple pesticide residues in corn.

[0054] Description of the drawings

[0055] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0056] Figure 1 It is the flow chart of the method steps of the present invention. Detailed implementation manners

[0057] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention.

[0058] Embodiment, as Figure 1 shown, a method for detecting pesticide residues in corn includes the following steps:

[0059] S1. Sampling the corn by the quartering method to obtain a corn sample, and performing crushing and weighing on the corn sample to obtain a corn sample to be tested;

[0060] S2. Add the corn sample to be tested to acetonitrile and ultrapure water, perform layering treatment to obtain the organic phase, concentrate and purify the organic phase to obtain the organic phosphorus pesticide solution to be detected and the organic chlorine pesticide solution to be detected;

[0061] S3. Detect the organic phosphorus pesticide solution to be detected and the organic chlorine pesticide solution to be detected respectively by a gas chromatograph to obtain pesticide chromatogram data;

[0062] S4. Take the organic phosphorus pesticide standard solution and the organic chlorine pesticide standard solution, prepare a series of concentration standard solutions for the organic phosphorus pesticide standard solution and the organic chlorine pesticide standard solution respectively, and detect the series of concentration standard solutions by a gas chromatograph to obtain pesticide standard concentration chromatogram data. According to the pesticide standard concentration chromatogram data, draw a peak area concentration standard curve;

[0063] S5. Extract the peak area from the pesticide chromatogram data, calculate the peak area through the peak area concentration standard curve to obtain the pesticide residue concentration. At the same time, construct a pesticide residue quantitative threshold, compare the pesticide residue concentration with the pesticide residue quantitative threshold, and conduct a re-inspection judgment.

[0064] Furthermore, the working principle of the present invention is illustrated by the following examples:

[0065] Suppose in a large corn planting base, recently it was found that when some corn was used for feed processing after harvest, livestock showed abnormal reactions, and it was suspected that it was related to pesticide residues in the corn. To accurately detect the pesticide residues in the corn and ensure food safety and livestock health, the corn pesticide residue detection method of the present invention was used for detection.

[0066] Prepare experimental materials and instruments. Randomly select 10 corn samples from different areas of the planting base, standard solutions with concentrations of 1000 mg / L of ethoprophos, monocrotophos, malathion, fenthion, isocarbophos, profenofos, metolachlor, fenvalerate, deltamethrin, cyhalothrin, procymidone and chlorfenapyr, acetonitrile, acetone, n-hexane, sodium chloride and ultrapure water, Florisil solid phase extraction column and 0.22 μm organic filter membrane, GM-K06 Geming kitchen machine (wall breaker), T-200 electronic balance, CSR-1-10Ⅱ ultrapure water device, T25 homogenizer, TTL-DCⅡ type nitrogen blower, Vortex-2 vortex mixer, GC-2010PLUS gas chromatograph equipped with a flame photometric detector, GC-2010PLUS gas chromatograph equipped with an electron capture detector and chromatographic workstation software.

[0067] For each selected corn sample, take samples by the quartering method, put the samples into a wall breaker and break them, and then accurately weigh 25.0 g with an electronic balance to obtain the corn sample to be tested.

[0068] Add 50 mL of acetonitrile and 30 mL of ultrapure water to the corn sample to be tested, place it in a homogenizer for 2 min, put the homogenized sample into a 100 mL stoppered measuring cylinder with 15.0 g of sodium chloride, shake it vigorously for 30 s, let it stand at room temperature for 30 min to separate the organic phase and the aqueous phase, use a pipette to draw 10 mL of the organic phase to obtain 10 mL of the organic phase to be tested, place the 10 mL of the organic phase to be tested in an 80 ° C water bath to heat it, and slowly blow it to near dryness with a nitrogen blower, and blow the nearly dry organic phase to be tested. Add 5 mL of acetone to the test solution, vortex mix for 30 seconds, and pass through a 0.22 μm organic filter membrane to obtain the organophosphorus pesticide test solution; add 50 mL of acetonitrile and 25 mL of ultrapure water to the corn sample, homogenize and extract for 2 minutes, and the subsequent operations are the same as the preparation of the organophosphorus pesticide test solution, only add 2 mL of n-hexane after blowing to nearly dryness and vortex mix, then purify with a Florisil solid phase extraction column, and finally make up to 5 mL with n-hexane, pass through a 0.22 μm organic filter membrane to obtain the organochlorine pesticide test solution.

[0069] A gas chromatograph equipped with a flame photometric detector, split injection, RTX-5 and wondacap-17 capillary columns was selected. The column temperature program was set as follows: the initial column temperature was 150°C for 2 min, then increased to 250°C at 8°C / min and maintained for 18 min; the carrier gas flow rate was 9 mL / min, the injection volume was 1 μL, the flame photometric detector temperature was 270°C, the injection port temperature was 220°C, the air flow rate was 90 mL / min and the split ratio was 3:1. The organophosphorus pesticide solution to be tested was injected and the obtained Obtain pesticide chromatogram data; select a gas chromatograph equipped with an electron capture detector, RTX-5 and Wondacap-1 capillary columns, set the column temperature program as an initial column temperature of 150°C for 2 min, increase to 270°C at 6°C / min and maintain for 18 min, injection volume 1μL, electron capture detector temperature 320°C, injection port temperature 200°C, gas flow rate 14mL / min and split ratio 10:1, inject the organochlorine pesticide to be tested solution, and obtain the pesticide chromatogram data.

[0070] Take 100 μL of 1000 mg / L organophosphorus pesticide standard solution, and dilute it with acetone to prepare 10 mL of series concentration standard solutions with concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L, and 0.4 mg / L respectively; take 100 μL of 1000 mg / L organochlorine pesticide standard solution, and dilute it with n-hexane to prepare 10 mL of series concentration standard solutions with concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L, and 0.4 mg / L respectively; detect the series concentration standard solutions, extract the peak area and the retention time corresponding to the peak area from the chromatogram data of the pesticide standard concentration, determine the pesticide type according to the retention time, and manually mark the standard solution concentration and the pesticide type; take the standard solution concentration as the abscissa and the peak area as the ordinate, and perform least squares linear regression through the chromatographic workstation software to obtain the peak area concentration standard curve of each pesticide type. For example, the peak area concentration standard curve of ethoprophos is Y = 2.84152×10 6 X.

[0071] Extract the peak area and the retention time from the pesticide chromatogram data, determine the pesticide type, and substitute the peak area into the corresponding peak area concentration standard curve to calculate the pesticide residue concentration. For example, if in the detection of a certain corn sample, ethoprophos is determined according to the retention time, and its peak area is 1.42076×10 5 , substituting it into the standard curve of ethoprophos, X can be obtained as 0.05 mg / kg; construct a pesticide residue quantitative threshold of 0.02 mg / kg, compare the calculated pesticide residue concentration with the threshold. If the pesticide residue concentration is greater than or equal to 0.02 mg / kg, then determine the residue concentration of this pesticide; if it is less than 0.02 mg / kg, then re-detect the pesticide residue in the corn.

[0072] The test results of corn samples from 10 different regions are as follows: Ethoprophos at 0.05 mg / kg and S-metolachlor at 0.03 mg / kg were detected in corn sample No. 1; Procymidone at 0.01 mg / kg was detected in corn sample No. 2; Lambda-cyhalothrin at 0.04 mg / kg was detected in corn sample No. 3; No pesticide was detected in corn sample No. 4; Fenthion at 0.06 mg / kg was detected in corn sample No. 5; Chlorfenapyr at 0.03 mg / kg was detected in corn sample No. 6; Fenvalerate at 0.025 mg / kg was detected in corn sample No. 7; Deltamethrin at 0.035 mg / kg was detected in corn sample No. 8; Isocarbophos at 0.07 mg / kg was detected in corn sample No. 9; Malathion at 0.04 mg / kg was detected in corn sample No. 10; Corn sample No. 2 was re-detected, and finally its procymidone residue concentration was determined to be 0.015 mg / kg.

[0073] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; modifying the technical solutions described in the foregoing embodiments, or equivalently replacing some of the technical features, does not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present application, and all should be included within the protection scope of the present application.

Claims

1. A method for detecting pesticide residues in corn, characterized in that, It includes the following steps: S1. Take samples of corn by the quartering method to obtain corn samples, crush and weigh the corn samples to obtain corn samples to be tested; S2. Add acetonitrile and ultrapure water to the corn samples to be tested, and perform layering treatment to obtain the organic phase. Concentrate and purify the organic phase to obtain the organic phosphorus pesticide solution to be detected and the organic chlorine pesticide solution to be detected; S3. Detect the organic phosphorus pesticide solution to be detected and the organic chlorine pesticide solution to be detected by a gas chromatograph respectively to obtain pesticide chromatogram data; S4. Take the organic phosphorus pesticide standard solution and the organic chlorine pesticide standard solution, prepare a series of concentration standard solutions for the organic phosphorus pesticide standard solution and the organic chlorine pesticide standard solution respectively, and detect the series of concentration standard solutions by a gas chromatograph to obtain pesticide standard concentration chromatogram data. According to the pesticide standard concentration chromatogram data, draw a peak area concentration standard curve; S5. Extract the peak area from the pesticide chromatogram data, calculate the peak area through the peak area concentration standard curve to obtain the pesticide residue concentration. At the same time, construct a pesticide residue quantitative threshold, compare the pesticide residue concentration with the pesticide residue quantitative threshold, and conduct a re-inspection judgment.

2. The corn pesticide residue detection method according to claim 1, characterized in that, The method for obtaining the corn samples to be tested: Take samples of corn by the quartering method to obtain corn samples, crush the corn samples with a wall breaker, and weigh the crushed corn samples with an electronic balance to obtain corn samples to be tested; The quartering method is a method used to reduce the sample amount and ensure the representativeness of the sample.

3. The method for detecting pesticide residues in corn according to claim 2, wherein The method for obtaining the organic phosphorus pesticide solution to be detected: Add acetonitrile and ultrapure water to the corn samples to be tested, and place them in a homogenizer for homogenization extraction. Put the homogenized corn samples to be tested into a stoppered graduated cylinder containing sodium chloride, shake and let stand at room temperature to obtain the organic phase and the aqueous phase; Extract the organic phase with a pipette to obtain the organic phase to be tested. Place the organic phase to be tested on an 80°C water bath and heat it. At the same time, pass nitrogen through a nitrogen blower to blow it to nearly dry, and add acetone to make up to a pre-set volume. Vortex mix the organic phase to be tested made up with acetone with a vortex mixer to obtain a pesticide-acetone mixture, and filter the pesticide-acetone mixture through an organic filter membrane to obtain the organic phosphorus pesticide solution to be detected; The homogenization extraction is a technical means applied in sample processing; The vortex mixing is a mixing technique applied in the field of chemical analysis.

4. The corn pesticide residue detection method according to claim 2, characterized in that, The method for obtaining the organic chlorine pesticide solution to be detected: Add acetonitrile and ultrapure water to the corn samples to be tested, and place them in a homogenizer for homogenization extraction. Put the homogenized corn samples to be tested into a stoppered graduated cylinder containing sodium chloride, shake and let stand at room temperature to obtain the organic phase and the aqueous phase; Extract the organic phase with a pipette to obtain the organic phase to be tested. Place the organic phase to be tested on an 80°C water bath and heat it. At the same time, pass nitrogen through a nitrogen blower to blow it to nearly dry. Add 2.0 mL of n-hexane to the organic phase to be tested blown to nearly dry, and vortex mix it with a vortex mixer to obtain the solution to be purified; The Florisil solid-phase extraction column was pre-rinsed successively with an acetone-n-hexane mixture and n-hexane. Under the condition that the liquid level in the Florisil solid-phase extraction column reached the surface of the Florisil adsorption layer, the solution to be purified was poured in, and the eluate was collected with a centrifuge tube. The eluate was heated to 50 °C, and at the same time, it was blown to near dryness by a nitrogen blower. n-Hexane was added to the eluate blown to near dryness to make up the volume to a pre-set volume, and it was vortex-mixed by a vortex mixer to obtain a pesticide n-hexane mixture. The pesticide n-hexane mixture was filtered through an organic filter membrane to obtain a test solution of organochlorine pesticides.

5. The corn pesticide residue detection method according to claim 3, characterized in that, The method for detecting the test solution of organophosphorus pesticides by a gas chromatograph: Select a gas chromatograph equipped with a flame photometric detector, split injection, an RTX-5 and a wondacap-17 capillary column. Set the column temperature program, carrier gas flow rate, injection volume, flame photometric detector temperature, injection port temperature, air flow rate and split ratio of the gas chromatograph. Inject the test solution of organophosphorus pesticides into the set gas chromatograph to obtain pesticide chromatogram data.

6. The corn pesticide residue detection method according to claim 4, characterized in that The method for monitoring the test solution of organochlorine pesticides by a gas chromatograph: Select a gas chromatograph equipped with an electron capture detector, an RTX-5 and a Wondacap-1 capillary column. Set the column temperature program, injection volume, electron capture detector temperature, injection port temperature, gas flow rate and split ratio of the gas chromatograph. Inject the test solution of organochlorine pesticides into the set gas chromatograph to obtain pesticide chromatogram data.

7. The method for detecting pesticide residues in corn according to claim 1, characterized in that, The method for separately preparing series concentration standard solutions of organophosphorus pesticide standard solutions and organochlorine pesticide standard solutions and detecting the series concentration standard solutions by a gas chromatograph: Take the organophosphorus pesticide standard solution, add acetone to the organophosphorus pesticide standard solution to prepare five series concentration standard solutions with organophosphorus pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L and 0.4 mg / L. Use the method for detecting the test solution of organophosphorus pesticides by a gas chromatograph for the five series concentration standard solutions with organophosphorus pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L and 0.4 mg / L to obtain pesticide standard concentration chromatogram data; Take the organochlorine pesticide standard solution, add n-hexane to the organochlorine pesticide standard solution to prepare five series concentration standard solutions with organochlorine pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / mL and 0.4 mg / L. Use the method for detecting the test solution of organochlorine pesticides by a gas chromatograph for the five series concentration standard solutions with organochlorine pesticide concentrations of 0.02 mg / L, 0.05 mg / L, 0.1 mg / L, 0.2 mg / L and 0.4 mg / L to obtain pesticide standard concentration chromatogram data; The organophosphorus pesticide standard solution is a solution with the concentrations of ethoprophos, monocrotophos, malathion, fenthion, isocarbophos and profenofos all being 1000 mg / L; The organochlorine pesticide standard solution is a solution with the concentrations of metolachlor, fenvalerate, deltamethrin, cyhalothrin, procymidone and chlorfenapyr all being 1000 mg / L.

8. The corn pesticide residue detection method according to claim 7, characterized in that, The method for obtaining the standard curve of peak area concentration by plotting according to the chromatogram data of pesticide standard concentrations: Extract the peak area and the retention time corresponding to the peak area from the chromatogram data of pesticide standard concentrations. Determine the type of pesticide corresponding to the peak area according to the retention time corresponding to the peak area, and manually mark the standard solution concentration and the type of pesticide corresponding to the peak area. With the standard solution concentration as the abscissa and the peak area as the ordinate, perform least-squares linear regression through the chromatographic workstation software to obtain the standard curve of peak area concentration for each type of pesticide; The types of pesticides include ethoprophos, monocrotophos, malathion, fenthion, isocarbophos, profenofos, metolachlor, fenvalerate, deltamethrin, cyhalothrin, procymidone and chlorfenapyr; The chromatographic workstation software is a professional software used to control the operation of chromatographic instruments, collect and process chromatographic data; The least-squares linear regression is a statistical method used to fit data by minimizing the sum of the squares of the errors.

9. The corn pesticide residue detection method according to claim 8, characterized in that, The method for obtaining the pesticide residue concentration: Extract the peak area and the retention time corresponding to the peak area from the chromatogram data of pesticide concentrations. Determine the type of pesticide corresponding to the peak area according to the retention time corresponding to the peak area, and substitute the peak area into the standard curve of peak area concentration of the corresponding type of pesticide for calculation to obtain the pesticide residue concentration.

10. The corn pesticide residue detection method according to claim 9, characterized in that, The method for constructing the quantitative threshold of pesticide residues and comparing the pesticide residue concentration with the quantitative threshold of pesticide residues for reinspection judgment: If the pesticide residue concentration is greater than or equal to the quantitative threshold of pesticide residues of 0.02 mg / kg, the pesticide residue concentration is obtained; If the pesticide residue concentration is less than the quantitative threshold of pesticide residues of 0.02 mg / kg, it indicates that the operation of corn pesticide residue detection is not standardized, and the corn pesticide residue detection is carried out again.

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