Method for detecting organochlorine pesticide residues in liquid milk

Abstract

The invention relates to the field of pesticide residue detection, in particular to a method for detecting organochlorine pesticide residues in liquid milk. The detection method disclosed by the invention is simple and convenient to operate, and can be used for simply and quickly removing impurities in a sample and simultaneously completing efficient purification by using a relatively small amount of organic solvent.

Description

Technical Field

[0001] The invention relates to the field of pesticide residue detection, and in particular to a method for detecting organochlorine pesticide residues in liquid milk. Background Art

[0002] Pesticide residues refer to the general term for pesticide precursors, toxic metabolites, degradation substances and impurities that remain in organisms, agricultural and sideline products or the natural environment after pesticide use. Pesticide residue detection is an important task, which involves the detection of pesticide residues in environmental media such as soil, water sources, and air to assess environmental quality and human health risks. Organochlorine pesticides are a type of persistent organic pollutants that are widely present in the environment and have high efficiency in insecticide, weed control and sterilization. As one of the classic pesticides, it has the characteristics of high toxicity, easy residue and difficult decomposition. Due to the long-term residual characteristics of organochlorine pesticides, this type of pesticide has received much attention in the study of pesticide residues in food. Regarding the relevant standards and regulations for organochlorine pesticide residues, there are national standards such as "GB5009.19-2008 Determination of multi-component residues of organochlorine pesticides in food" and "GB23200.86-2016 National Food Safety Standard Determination of multiple organochlorine pesticide residues in milk and dairy products by gas chromatography-mass spectrometry / mass spectrometry".

[0003] The structure of liquid emulsion matrix is ​​relatively complex. When detecting trace pesticides and heavy metals in it, it is necessary to extract and purify the components to be tested, that is, to perform sample analysis after pretreatment. Therefore, sample pretreatment technology is a very critical link, which directly affects the accuracy and effectiveness of the test results. Existing pretreatment methods include liquid-liquid extraction technology (LLE), solid phase extraction technology (SPE), solid phase microextraction technology (SPME), matrix dispersed solid phase extraction technology (MSPD), gel permeation chromatography technology (GPC), turbidity point extraction technology (CPE), QuEChERS technology, etc.

[0004] Liquid-liquid extraction (LLE): This technology is relatively traditional. It uses the different distribution coefficients or solubilities of the component to be tested and other components in the sample in two immiscible (or slightly soluble) solvents. Through repeated extraction, the non-components to be tested are transferred to other solvents, and most of the components to be tested are extracted and purified. This technology has the characteristics of good separation effect, high recovery rate, strong operability, easy control, and large-scale operation. However, the operation steps are relatively cumbersome, and the extractants are mostly organic solvents, especially organic solvents containing halogens, which are harmful to the health of the experimenter and easily cause a certain degree of environmental pollution.

[0005] Solid phase extraction (SPE): mainly uses the principle of selective adsorption of the target and then elution, that is, after the sample passes through the extraction column, the component to be tested is adsorbed on the extraction column, and the interfering component flows out of the extraction column, and then an appropriate solvent is used to elute the target adsorbed in the extraction column to achieve the purpose of separation and purification. This technology requires activation, sample loading, and elution in existing products; the required experimental time is relatively long.

[0006] Gel Permeation Chromatography (GPC): This technology is effective in removing macromolecular substances such as pigments, fats, and proteins from samples. The stationary phase is gel particles, which can move with the mobile phase. Large molecular weight substances move along the gaps between gel particles and have a shorter retention time (Rt) in the chromatographic column; small molecular weight substances can diffuse into the interior of the gel particles and have a longer retention time (Rt) in the chromatographic column. The purpose of purifying and enriching the components to be tested can be achieved through the difference in retention time of different components. However, since gel chromatography is based on the difference in molecular weight of the substance as the basis for separation, the difference in molecular weight is only reflected in the difference in flow rate, so the flow rate must be strictly controlled during separation. Therefore, the separation operation is generally slow. Moreover, it is difficult to achieve a good separation effect for substances with similar molecular weights. In addition, gel chromatography requires that the sample viscosity should not be too high, and gel particles sometimes have non-specific adsorption.

[0007] QuEChERS method: Anastassiades, Lehotay and others created the QuEChERS method in 2003. Each letter in the method name represents an advantage of this method, which stands for Quick, Easy, Cheap, Effective, Rugged and Safe. This method was originally used to detect a variety of pesticide residues in vegetables or fruits, but has now been expanded to many fields such as pesticide residues in agricultural products and foods, poisons in blood, and mycotoxins in food. The application range of the QuEChERS method is very wide, but there are still some disadvantages: for samples with low water content or high fat content, the purification effect is not ideal, the extraction efficiency is low, and the loss in the purification process is large.

[0008] Currently, the most widely used pesticide residue analysis technologies include chromatography, mass spectrometry and immunoassay, among which chromatography includes gas chromatography (GC) and liquid chromatography (LC).

[0009] Gas chromatography (GC): The difference in physical properties of materials (such as boiling point, polarity, adsorption, etc.) is used to separate the test component from other components. This technology can be used for easily gasified, high temperature resistant organophosphorus, organochlorine and other pesticides. After separation, the test components are detected by flame photometric detector (FID), nitrogen phosphorus detector (NPD), and electron capture detector (ECD) to obtain chromatographic elution diagrams for qualitative or quantitative analysis. This technology is simple, fast, efficient, and has a wide range of selection. Ban Qiuli et al. used gas chromatography to detect the pesticide methyl isoflavone in vegetables. When the content of methyl isoflavone was 0.25 mg / kg, the expanded uncertainty of the test result was 0.03 mg / kg; Wang Jinyun et al. used gas chromatography-electron capture detector to detect and analyze 8 pesticide residues in wheat; Ji Jinmei used gas chromatography technology to detect 4 pesticide residues of fenpropimorph, acetamiprid, fipronil, and pyraclostrobin in vegetables, and all achieved good detection results.

[0010] Although the existing technology can meet the needs of pesticide residue detection to a certain extent, there are still various problems. First, it is necessary to perform repeated extractions, the operation steps are complicated, the experiment time is long, and a variety of organic solvents are required that may cause subsequent environmental pollution; second, the existing extraction and purification methods may result in a low recovery rate of organochlorine pesticides, affecting the accuracy of the test results. Therefore, the current method for detecting organochlorine pesticide residues in liquid milk still needs to be improved. Summary of the invention

[0011] In view of this, the present invention provides the above-mentioned existing pretreatment methods for organochlorine pesticide residues, which still have many deficiencies. Therefore, the art is in urgent need of a new purification filler and pretreatment method for detecting organochlorine pesticides in animal-derived foods.

[0012] Therefore, in a first aspect, the present invention provides a method for detecting organochlorine pesticide residues in liquid milk, comprising the following steps:

[0013] 1) Take the mixed liquid milk, extract it once with acetonitrile, then add salt bag, shake, centrifuge and take the supernatant;

[0014] 2) adding the supernatant to a multi-walled carbon nanotube purification column for direct purification;

[0015] 3) The purified solution is concentrated to near dryness, and n-hexane is added to dissolve and constant volume to obtain a sample solution to be tested, which is then tested by gas chromatography.

[0016] In some embodiments, the liquid-to-solid ratio of the acetonitrile to the liquid emulsion to be tested is (10-30) mL:10 g.

[0017] In some embodiments, the extraction time of the acetonitrile extracting the liquid milk is at least 5 minutes.

[0018] In some embodiments, the salt package is selected from sodium chloride, sodium chloride and anhydrous sodium sulfate, and anhydrous sodium acetate and anhydrous magnesium sulfate; in a preferred embodiment, the salt package is anhydrous sodium acetate and anhydrous magnesium sulfate; in a preferred embodiment, the salt package is anhydrous sodium acetate and anhydrous magnesium sulfate in a mass ratio of 1:1 to 1:5.

[0019] In some embodiments, the multi-walled carbon nanotube purification column is a multi-walled carbon nanotube purification column for high-lipid matrix.

[0020] In some embodiments, the sample solution is filtered through an organic filter membrane before being tested on the machine; in a preferred embodiment, the filtration is performed using an organic filter membrane with a pore size of less than 0.45 μm.

[0021] In some embodiments, the gas chromatography uses an ECD electron capture detector and a non-polar chromatographic column for detection.

[0022] In some embodiments, the gas chromatography is programmed temperature gas chromatography.

[0023] In some embodiments, the organochlorine pesticide includes at least one of the following pesticides: α-BHC, β-BHC, lindane, δ-BHC, o,p'-DDT (O,P'-DDT), p,p'-DDT (P,P'-DDT), p,p'-DDE (P,P'-DDE), p,p'-DDD (P,P'-DDD), heptachlor, heptachlor epoxide A, heptachlor epoxide B, aldrin, dieldrin, cis-chlordane, trans-chlordane, oxychlordane, α-endosulfan, β-endosulfan, and endosulfan sulfate.

[0024] Beneficial effects of the invention: The invention provides a method for detecting pesticide residues in liquid milk, which is easy to operate, can use less organic solvent (only a small amount of acetonitrile and n-hexane), simply (single extraction, purification column does not need to be activated), and quickly (the detection time of a single sample is only 40 minutes) to remove impurities in the sample and complete efficient purification. In addition, the method of the invention can analyze and detect a variety of organochlorine pesticides, and has the advantages of being applicable to liquid milk and its products, and having a high recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other implementation plans can be obtained based on these drawings without paying creative work.

[0026] Figure 1 The chromatograms of the standard samples under three conditions of programmed temperature increase are shown in Figure 2. DETAILED DESCRIPTION

[0027] The present invention will be described clearly and completely below in conjunction with the embodiments and drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments that can be obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0028] As described above, the methods for detecting organochlorine pesticide residues in the existing technology, especially the methods for detecting organochlorine pesticide residues in high-fat samples such as liquid milk, have problems such as multiple repeated extractions, complicated operation steps, long experimental time, and the need for multiple organic solvents that may cause subsequent environmental pollution. At the same time, the existing extraction and purification methods may result in a low recovery rate of organochlorine pesticides, affecting the accuracy of the test results.

[0029] The present invention aims to provide an improved method for detecting organochlorine pesticide residues in liquid milk, which method only requires a small amount of acetonitrile for a single extraction, and is combined with a purification column that does not require activation to quickly remove impurities in the sample while achieving efficient purification.

[0030] Therefore, in a first aspect, the present invention provides a method for detecting organochlorine pesticide residues in liquid milk, comprising the following steps:

[0031] 1) Take the mixed liquid milk, extract it once with acetonitrile, then add salt bag, shake, centrifuge and take the supernatant;

[0032] 2) adding the supernatant to a multi-walled carbon nanotube purification column for direct purification;

[0033] 3) The purified solution is concentrated to near dryness, and n-hexane is added to dissolve and constant volume to obtain a sample solution to be tested, which is then tested by gas chromatography.

[0034] The term "liquid milk" in the present invention generally refers to liquid dairy products made from fresh raw cow or goat milk or raw cow or goat milk, which have been processed through purification, homogenization, sterilization and other processes, including but not limited to pasteurized milk, sterilized milk, formulated milk, etc. Preferably, the liquid milk is raw cow milk.

[0035] It is known that the extractants commonly used in the prior art for pretreatment of food pesticide residue detection include acetone, ethyl acetate, acetonitrile, etc. The initial research objects of the QuEChERS method were mainly plant-derived foods such as fruits, vegetables and other agricultural products with high water content. Acetone is too soluble in water and is difficult to separate from the water in the matrix, which is difficult to separate and affects the test results; ethyl acetate cannot completely extract highly polar pesticides from the aqueous matrix, so it is not a suitable choice; acetonitrile has stronger selectivity for pesticides in fruit and vegetable samples, is not easy to extract excess impurities, and can be easily separated from the water in the matrix by salting out, so acetonitrile is finally selected as the most suitable extractant for the QuEChERS method. Experimental data show that in terms of recovery, for non-polar pesticides, there is no obvious difference between acetonitrile and ethyl acetate, but acetonitrile can provide more stable results and a smaller relative standard deviation (RSD) value; for polar pesticides (such as chlorpyrifos, methyl parathion, acephate, etc.), the extraction efficiency of acetonitrile is much higher. The inventors designed the experimental scheme from the three aspects of satisfying the extraction efficiency and detection efficiency of 60%-120% recovery rate and reducing the amount of organic solvent used when establishing the detection method of the present invention. Specifically, the inventors used 5mL, 10mL, 20mL, 30mL, 40mL of acetonitrile (10g sample to be tested) and 2 minutes, 3 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes of extraction time respectively when conducting experimental verification. The inventors found in the experiment that when the extraction time was less than 5 minutes, the extraction effect was not good, and when it was more than 5 minutes, the extraction effect was not much different. The results show that a good recovery rate can be obtained when the liquid-solid ratio of acetonitrile to the sample to be tested is (10-30) mL:10 g, and the extraction time is at least 5 minutes (e.g., 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 15 minutes, 20 minutes, etc.), and a better recovery rate can be obtained when the liquid-solid ratio of acetonitrile to the sample to be tested is 20 mL:10 g. Under this condition, only one extraction with acetonitrile can obtain the detection results of 19 organochlorine pesticides that meet the requirements. Therefore, in some embodiments, the liquid-solid ratio of acetonitrile to the liquid emulsion to be tested is (10-30) mL:10 g, and the extraction time of acetonitrile is at least 5 minutes; in a preferred embodiment, the liquid-solid ratio of acetonitrile to the liquid emulsion to be tested is 20 mL:10 g.

[0036] In addition, due to the high volatility of acetonitrile, it is easy to cause pollution inside the instrument, and it is also easy to dissolve rubber and vulcanized rubber. Therefore, when using acetonitrile as an extractant, it is necessary to select suitable materials to avoid using parts that will be corroded by acetonitrile, and solvent conversion is required after extraction. The inventor took this problem into consideration and concentrated the acetonitrile to near dryness by rotary evaporation after acetonitrile extraction. At the same time, it was found in the experiment that the rotary evaporation process is preferably carried out under a nitrogen atmosphere or a vacuum state, otherwise the recovery rate of α-hexachloride will be reduced. In the present invention, the term "near dryness" refers to the absence of a fluid liquid in the concentrated product. Therefore, in some embodiments, in step 3), the purified liquid is concentrated to near dryness by rotary evaporation to remove the acetonitrile therein. Preferably, the rotary evaporation is carried out under a nitrogen atmosphere or a vacuum state.

[0037] The salt bag is an important component of the QuEChERS method. Its addition helps to improve the purity of the extract and reduce the contamination of the chromatographic column, thereby improving the analysis results. Its preparation and selection are crucial to the accuracy and reliability of the experimental results. Therefore, in the present invention, the inventor optimizes the salt bag according to the sample type (liquid milk) and analysis requirements. In some embodiments, the salt bag is selected from sodium chloride, sodium chloride and anhydrous sodium sulfate, and anhydrous sodium acetate and anhydrous magnesium sulfate. In a preferred embodiment, the salt bag is anhydrous sodium acetate and anhydrous magnesium sulfate, and the anhydrous magnesium sulfate in the salt bag plays a role in absorbing impurities such as moisture and fatty acids, and anhydrous sodium acetate is used as a salting-out agent and buffer salt to maintain stability during the extraction process. In a preferred embodiment, the mass ratio of anhydrous sodium acetate and anhydrous magnesium sulfate is 1:1 to 1:5; in a more preferred embodiment, the mass ratio of anhydrous sodium acetate and anhydrous magnesium sulfate is 1:4.

[0038] It is known to those skilled in the art that the pretreatment method of the sample to be tested needs to be determined according to the matrix, composition and properties of the sample. Liquid milk, as an animal-derived product, has obvious differences in composition from plant-derived agricultural products, and the pretreatment is also different. The main components of liquid milk include protein (such as casein, whey protein), fat, lactose, various minerals (such as calcium, phosphorus, potassium, etc.), vitamins, etc. The composition of plant-derived agricultural products varies according to the specific type, such as starch, cellulose, various plant proteins, vitamins, minerals, phytochemicals, etc. Therefore, most plant-derived products are extracted with organic reagents, and the sample liquid needs to remove the interference from pigments after extraction. Animal-derived samples need to consider the interference from fat, small molecule proteins, and amino acids, so a purification column is usually used to purify the sample liquid after extraction to avoid instrument contamination. When selecting a suitable purification column, the inventor compared different purification columns and found that most purification columns (such as CNW purification columns) need to be activated-enriched-eluted, with complex steps, a large amount of organic reagents, and poor recovery of some pesticide residues (the recovery rate of chlordane oxide and endosulfan sulfate is less than 60%). Therefore, the inventor tried to use the MPFC-QuEChERS (high fat) purification column purchased from Beijing Green Cotton Technology, because it does not require activation and is simple to operate, although the product introduction and prior art materials show that the purification column is suitable for use in plant-based foods. The inventor unexpectedly found that by combining the selection of extraction reagents and the adjustment of the extraction scheme, the MPFC-QuEChERS (high fat) purification column was used to purify the liquid milk sample, and an unexpected purification effect was obtained, thereby achieving the goal of improving the accuracy of the test results and improving the detection efficiency on the basis of simplifying the pre-treatment method. Therefore, in some embodiments, the multi-walled carbon nanotube purification column is a multi-walled carbon nanotube purification column for high-fat matrices. In a preferred embodiment, the multi-walled carbon nanotube purification column is the MPFC-QuEChERS (high fat) purification column of Beijing Green Cotton Technology Co., Ltd.

[0039] In the present invention, since the sample supernatant is directly purified by column (without enrichment-elution process), the speed of supernatant passing through purification column has a great influence on the recovery result, so it is very important to control the flow rate. If the speed is too fast, the target and impurities cannot be fully separated, and if the speed is too slow, the carrying capacity of purification column filler is overloaded, which can lead to inaccurate test results. The inventor verified from three different flow rates (0.5mL / minute, 1.0mL / minute, 2.0mL / minute), and found that only at a flow rate of 1.0mL / minute, the flow rate recovery result can meet the 60%-120% requirement. Therefore, in some embodiments, the column speed of the supernatant in step 2) is 1mL / minute.

[0040] Since the pre-treatment method adopted by the present invention is only a single extraction, and is directly purified by column, the obtained sample solution may contain particles or impurities that affect the subsequent gas chromatography. Therefore, in order to further improve the accuracy of the detection method of the present invention, in some embodiments, the sample solution is filtered through an organic filter membrane before being tested on the machine. In a preferred embodiment, an organic filter membrane with a pore size of less than 0.45 μm is used for filtration. In a more preferred embodiment, an organic filter membrane with a pore size of 0.22 μm is used for filtration.

[0041] In addition, the inventors also conducted corresponding comparative experiments on the selection of chromatographic columns when improving the detection method. Specifically, HP-5 (30m×0.32mm×0.25μm), DB-5 (60m×0.25mm×0.25μm), and CD-1701 (30m×0.25mm×0.25μm) capillary chromatographic columns were selected for analysis and comparison, that is, the same concentration of the components to be tested were mixed with standard samples for chromatographic column separation experiments, and the response values ​​and separation degrees of the 19 components of organochlorine pesticides to be tested were compared. Finally, DB-5 (60m×0.25mm×0.25μm) capillary chromatographic column was selected. Therefore, in some embodiments, the gas chromatography method uses an electron capture detector and a non-polar chromatographic column for detection. In a preferred embodiment, the non-polar chromatographic column is a DB-5 chromatographic column.

[0042] Furthermore, it is known to those skilled in the art that a mixture with a large difference in boiling point can be analyzed and determined by using a programmed temperature rise mode, by setting the initial temperature, heating rate, holding time and end temperature, wherein the boiling point temperature of the lowest boiling point component in the mixture to be measured is used as the upper limit of the initial temperature, a temperature lower than the lowest boiling point is selected as the initial temperature, and the holding time is set to ensure that the sample can be completely vaporized; the end temperature should be set according to the highest boiling point temperature of the component to be measured below the highest temperature of the chromatographic column. The use of a programmed temperature rise mode can shorten the analysis cycle, improve the chromatographic peak shape, and increase the chromatographic separation and detection sensitivity. The inventors studied and compared three programmed temperature increases: programmed temperature increase one: set the initial temperature to 60°C (maintain for 1 minute), and increase the temperature to 280°C at a rate of 10°C / min (maintain for 10 minutes); programmed temperature increase two: set the initial temperature to 90°C (maintain for 2 minutes), increase the temperature to 200°C at a rate of 40°C / min (maintain for 1 minute), increase the temperature to 230°C at a rate of 5°C / min (maintain for 2 minutes), and increase the temperature to 280°C at a rate of 40°C / min (maintain for 5 minutes); programmed temperature increase three: set the initial temperature to 90°C (maintain for 1 minute), increase the temperature to 170°C at a rate of 40°C / min (not maintained), increase the temperature to 230°C at a rate of 1.5°C / min (maintain for 17 minutes), and increase the temperature to 280°C at a rate of 40°C / min (maintain for 5 minutes), and select the optimal chromatographic column temperature condition as programmed temperature increase three through the separated chromatographic elution diagram. Therefore, in some embodiments, the gas chromatography in the detection method is a programmed temperature gas chromatography. In a preferred embodiment, the programmed temperature conditions of the gas chromatography are as follows (programmed temperature three): initial temperature 90°C (held for 1 minute), heated to 170°C (not held) at a heating rate of 40°C / min, heated to 230°C (held for 17 minutes) at a heating rate of 1.5°C / min, and heated to 280°C (held for 5 minutes) at a heating rate of 40°C / min.

[0043] Example

[0044] The present invention is described in more detail below in conjunction with the embodiments. The test methods in the following embodiments are conventional methods unless otherwise specified. The test materials used in the following embodiments are obtained by purchasing from conventional reagent stores unless otherwise specified. It should be noted that the above summary of the invention and the detailed description below are only for the purpose of specifically illustrating the present invention and are not intended to limit the present invention in any way.

[0045] Example 1.19 components two levels of spike recovery results

[0046] Sample pretreatment method: weigh 10.0g liquid milk (taking raw milk as an example), put it in a 50mL centrifuge tube, add 20mL acetonitrile, vortex and shake for 5 minutes, remove it, add 6g anhydrous magnesium sulfate and 1.5g anhydrous sodium acetate, shake for 1 minute, let it stand and cool to room temperature, shake it again for 1 minute, centrifuge it at 10000rpm / 5 minutes, pass the supernatant through the column at a speed of 1mL / min, take 10mL of the filtrate into a rotary evaporator, concentrate to near dryness (you can choose to concentrate and evaporate to dryness at 40℃±5℃ under nitrogen filling conditions, or concentrate and evaporate to dryness under vacuum conditions through a vacuum device), dissolve it in n-hexane to make it dilute to 5mL, and finally filter the fixed volume sample through a 0.22μm organic filter membrane to obtain the sample solution to be tested by gas chromatography.

[0047] Gas chromatography detection conditions:

[0048] Inlet temperature: 250℃

[0049] Detector temperature: 300°C

[0050] Diversion method: No diversion

[0051] Tail blowing: 50mL / min

[0052] Carrier gas: Nitrogen

[0053] Column flow rate: 0.9mL / min

[0054] Injection volume: 1.0 μL

[0055] Chromatographic column: DB-5, 60m×0.25mm×0.25μm.

[0056] Program temperature rise: initial temperature 90°C (held for 1 minute), increased to 170°C at a heating rate of 40°C / min (not held), increased to 230°C at a heating rate of 1.5°C / min (held for 17 minutes), and increased to 280°C at a heating rate of 40°C / min (held for 5 minutes).

[0057] Calculation of recovery rate:

[0058] Recovery rate = (S3-S1) / S2×100%

[0059] Where: S1 is the background content (μg / 100g), S2 is the theoretical addition amount (μg / 100g), and S3 is the detected content of the spiked sample (μg / 100g).

[0060] Results: The recoveries of α-BHC, β-BHC, γ-BHC (lindane), δ-BHC, o,p'-DDT (O,P'-DDT), p,p'-DDT (P,P'-DDT), p,p'-DDE (P,P'-DDE), p,p'-DDD (P,P'-DDD), heptachlor, heptachlor epoxide A, heptachlor epoxide B, aldrin, dieldrin, cis-chlordane, trans-chlordane, chlordane oxide, α-endosulfan, β-endosulfan and endosulfan sulfate at two concentration levels are shown in Tables 1-1 to 1-19.

[0061] Table 1-1α-BHC recovery rate test data table

[0062]

[0063] Table 1-2 β-BHC Recovery Rate Test Data Table

[0064]

[0065] Table 1-3 γ-BHC recovery rate test data table

[0066]

[0067] Table 1-4 δ-BHC recovery rate test data table

[0068]

[0069] Table 1-5 Heptachlor recovery rate test data table

[0070]

[0071] Table 1-6 Aldrin recovery rate test data table

[0072]

[0073] Table 1-7 Heptachlor Epoxide B Recovery Rate Test Data Table

[0074]

[0075] Table 1-8 Chlordane Oxidation Recovery Rate Test Data Table

[0076]

[0077] Table 1-9 Heptachlor Epoxide A Recovery Rate Test Data Table

[0078]

[0079] Table 1-10 Trans-Chlordane Recovery Rate Detection Data Table

[0080]

[0081] Table 1-11α-Endosulfan recovery rate test data table

[0082]

[0083] Table 1-12 Cis-chlordane recovery rate test data table

[0084]

[0085] Table 1-13 P, P'-DDE recovery rate test data table

[0086]

[0087] Table 1-14 Dieldrin recovery rate test data table

[0088]

[0089] Table 1-15β-endosulfan recovery rate test data table

[0090]

[0091] Table 1-16P, P'-DDD recovery rate test data table

[0092]

[0093] Table 1-17O,P'-DDT recovery rate test data table

[0094]

[0095] Table 1-18 Endosulfan sulfate recovery rate test data table

[0096]

[0097] Table 1-19 P, P'-DDT recovery rate test data table

[0098]

[0099] When the sampling amount is 10g and the fixed volume is 10mL, the detection limits of α-BHC, β-BHC, γ-BHC, δ-BHC, P,P'-DDE, P,P'-DDD, O,P'-DDT, P,P'-DDT, aldrin, α-endosulfan, dieldrin, β-endosulfan, and endosulfan sulfate are 0.002mg / kg, the detection limits of heptachlor, heptachlor epoxide B, and heptachlor epoxide A are 0.001mg / kg, and the detection limits of chlordane oxide, cis-chlordane, and trans-chlordane are 0.000 4mg / kg; the quantification limits of α-BHC, β-BHC, γ-BHC, δ-BHC, P,P'-DDE, P,P'-DDD, O,P'-DDT, P,P'-DDT, aldrin, α-endosulfan, dieldrin, β-endosulfan, and endosulfan sulfate are 0.002mg / kg, the quantification limits of heptachlor, heptachlor epoxide B, and heptachlor epoxide A are 0.001mg / kg, and the quantification limits of chlordane oxide, chlordane homeopathic, and trans-chlordane are 0.0004mg / kg; it can meet the requirements of "GB 2763-2021 National Food Safety Standard Maximum Residue Limits of Pesticides in Food".

[0100] Example 2. Comparison of recovery rates between the prior art method and the method of the present invention

[0101] In order to further compare the extraction and purification effects of the method of the present invention with the prior art method, the inventors used the extraction method that is more commonly used and has better effects in the prior art to detect the recovery rate of the same 19 organochlorine pesticides. The specific implementation steps of the method are shown in Tables 1-20. It can be clearly seen from Tables 1-20 that compared with the method in the prior art, the method of the present invention has simpler steps, uses less organic solvent, and has higher extraction and purification efficiency.

[0102] Table 1-20 Comparison of sample extraction and purification methods

[0103]

[0104] The experimental results show that among the 14 groups of sample data processed by the method of the present invention, the recovery rates of most of the organochlorine pesticide residues are better or equivalent to the recovery rates obtained by the prior art methods. In order to more intuitively show this point, the inventor selected the second group of data using the method of the present invention for comparison in Table 1-21. From the recovery rate point of view, the recovery rates of at least 17 organochlorine pesticide residues are better than those of the original method, and the recovery rates of 2 organochlorine pesticide residues are equivalent to those of the original method. In summary, the method of the present invention has higher accuracy, data stability and reliability, and can better meet the detection requirements.

[0105] Table 1-21 Recovery rate comparison table

[0106]

Claims

1. A method for detecting organochlorine pesticide residues in liquid milk, comprising the following steps: 1) Take the mixed liquid milk, extract it once with acetonitrile, then add salt bag, shake, centrifuge and take the supernatant; 2) adding the supernatant to a multi-walled carbon nanotube purification column for direct purification; 3) The purified solution is concentrated to near dryness, and n-hexane is added to dissolve and constant volume to obtain a sample solution to be tested, which is then tested by gas chromatography.

2. The method of claim 1, wherein the liquid-to-solid ratio of acetonitrile to the liquid emulsion to be tested is (10-30) mL:10 g.

3. The method of claim 1 or 2, wherein the extraction time of extracting the liquid milk using the acetonitrile is at least 5 minutes.

4. The method of any one of claims 1 to 3, wherein the salt bag is selected from sodium chloride, sodium chloride and anhydrous sodium sulfate, and anhydrous sodium acetate and anhydrous magnesium sulfate.

5. The method of claim 4, wherein the salt bag is anhydrous sodium acetate and anhydrous magnesium sulfate, preferably anhydrous sodium acetate and anhydrous magnesium sulfate in a mass ratio of 1:1 to 1:

5. 6 . The method according to claim 1 , wherein the multi-walled carbon nanotube purification column is a multi-walled carbon nanotube purification column for high-fat matrix.

7. The method according to any one of claims 1 to 6, wherein the sample solution is filtered through an organic filter membrane before being tested on the machine, and preferably, the pore size of the organic filter membrane is less than 0.45 μm.

8. The method according to any one of claims 1 to 7, wherein the gas chromatography is detected using an electron capture detector and a non-polar chromatographic column.

9. The method of claim 8, wherein the gas chromatography is programmed temperature gas chromatography.

10. The method according to any one of claims 1 to 9, wherein the organochlorine pesticide comprises at least one of the following pesticides: α-BHC, β-BHC, lindane, δ-BHC, o,p'-DDT, p,p'-DDT, p,p'-DDE, p,p'-DDD, heptachlor, heptachlor epoxide A, heptachlor epoxide B, aldrin, dieldrin, cis-chlordane, trans-chlordane, oxychlordane, α-endosulfan, β-endosulfan, and endosulfan sulfate.

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