Method for detecting organochlorine pesticide in milk through lipid removal dispersive solid-phase extraction

Abstract

The invention discloses a method for detecting organochlorine pesticide in milk through lipid removal dispersive solid-phase extraction. The method comprises the following steps: (1) preparing caprylic aldehyde modified chitosan copolymer C8-CsM; (2) removing lipid in milk by adopting the C8-CsM prepared in the step (1): extracting and purifying a milk sample to obtain a to-be-detected solution; and (3) detecting the organochlorine pesticide in the to-be-detected solution obtained in the step (2) by adopting a GC-HRMS method, and quantifying by adopting an external standard method. The caprylic aldehyde modified chitosan copolymer is used as a lipid removal dispersive solid-phase extraction agent, sample extraction and purification conditions are optimized, the GC-HRMS detection method for 24 organochlorine pesticides in milk is established, and the method is low in quantitation limit, high in sensitivity and recovery rate, simple to operate, reliable in result and good in repeatability.

Description

Technical Field

[0001] The invention belongs to the technical field of organochlorine pesticide detection, and specifically relates to a method for detecting organochlorine pesticides in milk by lipid removal dispersed solid phase extraction. Background Art

[0002] Organochlorine pesticides are a class of artificially synthesized broad-spectrum and highly effective insecticides. Swiss scientist Muller won the Nobel Prize for discovering the insecticidal effect of DDT in 1938. Subsequently, countries such as Britain and France successively developed organochlorine pesticides such as 666, chlordane, heptachlor, aldrin, and dieldrin. As the organochlorine pesticide family continues to grow, the large-scale use of various organochlorine pesticides has exposed their shortcomings such as strong fat solubility, difficulty in degradation, and easy accumulation in organisms, which are easy to cause harm to the human body. The United States, Sweden and other countries began to stop production and ban the use of DDT in the 1970s. my country also began to ban the production of organochlorine pesticides in the early 1980s and completely stopped the use of organochlorine pesticides in the early 1990s. However, due to the long residual period of organochlorine pesticides, there are still reports of organochlorine pesticides being detected in food in some areas. As a beneficial source of protein and calcium for the human body, milk has an increasing per capita consumption. Cows ingest residual organochlorine pesticides in the environment through forage and drinking water, which results in organochlorine pesticides being detected in milk. Although the residual amount is very low, long-term drinking of milk that may contain pesticide residues will harm human health. Therefore, it is necessary to establish a convenient, fast and accurate detection method for organochlorine pesticides to ensure the quality and safety of milk.

[0003] Commonly used analytical methods for trace organochlorine pesticides in food include gas chromatography (with electron capture detector), gas chromatography-tandem mass spectrometry, liquid chromatography-tandem mass spectrometry, etc. In recent years, gas chromatography-high-resolution mass spectrometry has also made great progress in the field of food pesticide residue detection. In addition to selecting highly sensitive detection instruments, sample pretreatment methods are equally important for the analysis of trace organochlorine pesticides. Commonly used sample pretreatment methods include liquid-liquid extraction, solid-liquid extraction, solid phase extraction columns, QuEChERS (quick, easy, cheap, effective, rugged, safety) method, etc. In food testing, it is often necessary to select appropriate treatment methods according to different food types, while taking into account solvent consumption and extraction efficiency of target compounds to obtain a stronger instrument response signal.

[0004] The main interfering substances in milk sample analysis are lipids and other compounds. Compared with common solid phase extraction columns and ion exchange dispersed solid phase extraction, lipid removal dispersed solid phase extraction can effectively adsorb interfering substances through size exclusion and other forms of action, retaining the target to be measured. At the same time, it shortens the sample pretreatment process and reduces the amount of solvent used. This method has been widely used in the analysis of trace compounds in the fields of food, chemical industry, and environment.

[0005] In the dispersed solid phase extraction method, the selection of adsorbent performance and type is particularly critical. Enhanced lipid removal (EMR-Lipid) is a polymer adsorbent that can selectively and efficiently adsorb lipid impurities through size exclusion and hydrophobic effects. However, whether it is EMR powder dispersed solid phase extraction or EMR solid phase extraction cartridge, it needs to be activated with water before use, or there is water in the extract. It is well known that moisture will affect the baseline of gas chromatography, which means that anhydrous magnesium sulfate needs to be used to remove water after the purification step to reduce the water content in the sample to be analyzed, which prolongs the operation process and increases the experimental cost. In addition, organochlorine pesticides are mostly extracted with n-hexane-acetone solvent to obtain the highest possible extraction effect, but water and n-hexane are not miscible. Therefore, using EMR as an adsorbent to remove lipids will cause stratification of the extract, affecting the purification effect. Summary of the invention

[0006] In view of the deficiencies of the above-mentioned prior art, the present invention provides a method for detecting organochlorine pesticides in milk by lipid removal dispersed solid phase extraction. The method adopts dispersed solid phase extraction to remove lipids in milk extract and retains the organochlorine pesticides to be analyzed. Chitosan copolymer modified with octanal is selected as adsorbent. The method has the advantages of good adsorption effect, short operation time and high sensitivity in organochlorine pesticide analysis.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for detecting organochlorine pesticides in milk by lipid removal dispersed solid phase extraction comprises the following steps:

[0009] (1) Preparing octanal-modified chitosan copolymer C8-CsM: chitosan powder is dissolved in acetic acid aqueous solution, stirred at room temperature to obtain a chitosan solution, octanal is mixed with ethanol to obtain an octanal ethanol solution, and liquid paraffin and Span80 are added to a round-bottom flask; the chitosan solution and the octanal ethanol solution are slowly added to the round-bottom flask in sequence, emulsified in a constant temperature oil bath, and then a glutaraldehyde crosslinking agent is slowly added. After the reaction, the liquid is cooled to room temperature, centrifuged, washed and dried to obtain C8-CsM;

[0010] (2) Using the C8-CsM prepared in step (1) to remove lipids from milk:

[0011] Extraction: Add NaCl to milk, use n-hexane-acetone vortex oscillation to extract organochlorine pesticides, and the supernatant after centrifugation is the milk extract;

[0012] Purification: Add the milk extract into the centrifuge tube containing C8-CsM, vortex to mix, take all the supernatant after centrifugation, blow it to near dryness with nitrogen, re-dissolve it with an organic solvent, and filter it to obtain the test solution;

[0013] (3) Detecting the organochlorine pesticides in the test solution obtained in step (2) by GC-HRMS and quantifying by external standard method.

[0014] Furthermore, in step (2), the organic solvent is acetonitrile, acetone, ethyl acetate or n-hexane.

[0015] Furthermore, the amount of C8-CsM used in step (2) is 0.2-0.6% of the mass of milk.

[0016] Furthermore, during the extraction process of step (2), when the centrifugation time is 2 minutes, the centrifugal speed is above 7000 rpm.

[0017] Furthermore, during the purification process of step (2), the vortex time is 1-10 min.

[0018] Furthermore, the instrument parameters of the GC-HRMS method in step (3) are: TG-5SilMS chromatographic column; carrier gas: high-purity helium; flow rate: 1.20 mL / min; heating method: programmed heating, injection port temperature: 300°C; injection method: splitless injection; injection volume: 1 μL; mass spectrometry scanning method: Full MS, positive mode; mass number range: 50-500 m / z.

[0019] Furthermore, the specific settings of the programmed temperature increase are: maintain at 55°C for 1 min, increase to 140°C at 40°C / min, maintain for 5 min, increase to 210°C at 2°C / min, increase to 280°C at 10°C / min, and maintain for 5 min.

[0020] The beneficial effects of the lipid removal dispersed solid phase extraction method for detecting organochlorine pesticides in milk of the present invention are as follows:

[0021] 1. The present invention adopts dispersed solid phase extraction as a method for purifying milk extract. Compared with the gel chromatography and solid phase extraction column methods in the national standard methods, the amount of solvent used is reduced. Combined with the highly sensitive GC-HRMS analysis instrument, an efficient analysis method for organochlorine pesticides in milk is established, providing technical support for ensuring the quality and safety of milk.

[0022] 2. The present invention adopts C8-CsM as the lipid purification material of milk extract, utilizes chitosan and glutaraldehyde to form a copolymer through emulsion cross-linking, and directly adds the modifier octanal during the polymerization process to obtain C8-CsM in one step, which simplifies the operation process of the conventional emulsion method, expands the application form of chitosan materials, and effectively removes lipid impurities in milk.

[0023] 3. The present invention adopts chitosan copolymer modified by octanal as lipid removal dispersed solid phase extractant, optimizes sample extraction and purification conditions, and establishes a GC-HRMS detection method for 24 organochlorine pesticides in milk. The method has low limit of quantification, high sensitivity, high recovery rate, simple operation, reliable results and good repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the FT-IR spectrum of C8-CsM prepared in Example 1.

[0025] Figure 2 This is the N2 adsorption-desorption isotherm of C8-CsM prepared in Example 1.

[0026] Figure 3 The recovery rates of 24 organochlorine pesticides at different extraction times are shown in Table 2.

[0027] Figure 4 It is the separation of milk samples at different centrifugal speeds during the extraction process.

[0028] Figure 5 is the recovery rate of 24 organochlorine pesticides at different C8-CsM dosages.

[0029] Figure 6 is the recovery rate of 24 organochlorine pesticides at different vortex times during the purification process.

[0030] Figure 7 is the recovery rate of 24 organochlorine pesticides treated with different re-dissolution solvents.

[0031] Figure 8 It is the spectrum of matrix-matched standards for 12 organochlorine pesticides (including 2,4'-DDT, 4,4'-DDD, 4,4'-DDE, cis-chlordane, trans-chlordane, dicofol, endosulfan sulfate, endrin aldehyde, endrin ketone, aldrin, dieldrin and 4,4'-DDT) under determined analytical conditions.

[0032] Fig. 9 It is the spectrum of matrix-matched standards of 12 organochlorine pesticides (including endrin, exocyclic heptachlor, heptachlor, hexachlorobenzene, methoxychlor, mirex, α-BHC, β-BHC, γ-BHC, β-endosulfan, α-endosulfan and δ-BHC) under determined analytical conditions.

[0033] Fig.10 The spectra of 2,4'-DDT and 4,4'-DDD under different chromatographic temperature programs. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention is clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Unless otherwise specified, the raw materials and instruments used in the following examples are all commercially available; the milk includes fresh milk, ultra-high temperature sterilized milk, pasteurized milk and high temperature sterilized milk.

[0036] Example 1. Preparation of C8-CsM

[0037] Chitosan is a natural polymer formed by removing part of the acetyl group of chitin. The copolymer with chitosan as the building unit has the characteristics of variable structure, flexible design, low density, high stability, good bioaffinity, etc., and has many applications in the field of separation. The present invention uses chitosan and glutaraldehyde to form a copolymer through emulsion cross-linking polymerization, and adds octanal as a modifier during the polymerization process to obtain an octanal-modified chitosan copolymer (C8-CsM). The specific preparation method is as follows:

[0038] 0.10 g of chitosan powder was dissolved in 10 mL of 3% (v / v) acetic acid aqueous solution, and a homogeneous transparent chitosan solution was obtained after stirring at room temperature. The solution was allowed to stand for defoaming. 80 mL of liquid paraffin and 2 mL of Span80 were added to a round-bottom flask. 1 mL of octanal was mixed with 4 mL of ethanol to obtain an octanal ethanol solution. The chitosan solution and the octanal ethanol solution were slowly dripped into the round-bottom flask in sequence, and emulsified in a 40° C. constant temperature oil bath for 2 h. Then 6 mL of glutaraldehyde crosslinking agent was slowly dripped, and the reaction was continued for 4 h. Finally, the liquid was cooled to room temperature, centrifuged at 7000 rpm for 6 minutes, and the precipitate was washed twice by centrifugation with acetone and anhydrous ethanol, and dried in an oven at 80° C. to obtain an octanal-modified chitosan copolymer.

[0039] The preparation method of C8-CsM is different from the conventional emulsion method, that is, preparing chitosan polymer first and then performing secondary modification, but preparing chitosan polymer modified with octanal in one step, which simplifies the operation process. In this method, the modifier octanal is directly added to the emulsion polymerization system, and octanal can occupy the cross-linking site of chitosan and glutaraldehyde, introduce a long carbon chain into the cross-linking system of chitosan and glutaraldehyde, increase the affinity of chitosan polymer and lipid, and thus enhance the removal effect of lipid.

[0040] Figure 1 This is the Fourier transform infrared (FT-IR) spectrum of C8-CsM. It can be seen from the figure that 3419cm -1 The absorption band is a broad absorption peak generated by the stretching vibration of OH and NH bonds, 2992 cm -1and 2885cm -1 The absorption peak at 1652 cm is attributed to the stretching vibration of the CH bond. -1 The stretching vibration peaks of C=O bond are located at 1058 cm -1 and 1030cm -1 By comparing the infrared spectra of chitosan copolymer and chitosan copolymer modified with octanal, it can be found that the 2918 cm -1 and 2878cm -1 The infrared signal at 1652 cm was enhanced, and the Schiff base produced by glutaraldehyde cross-linking reacted to generate a new group, imine (-N=CH-), which led to the -1 The peak at 40° was enhanced, which verified the formation of chitosan copolymer modified by octanal.

[0041] Figure 2 The N2 adsorption-desorption isotherm of C8-CsM is similar to the slit pore structure of the IV type isotherm. Capillary condensation occurs only when the pressure is close to the saturated vapor pressure. During evaporation, the slits are not parallel and the Kelvin radius changes, so the desorption curve slowly decreases, and the interval at the narrow end of the slit is very small, resulting in a small adsorption loop. The above characteristics indicate that the porosity of C8-CsM is very low and the specific surface area is very small.

[0042] Example 2, preparation of standard solution

[0043] 2.1. Preparation of standard solution

[0044] Accurately pipette a certain amount of liquid standard products (1000 mg / L, n-hexane as solvent) of 24 commercial organochlorine pesticides, dilute with n-hexane to obtain a 1.0 mg / L standard solution, and store in a refrigerator at 4°C.

[0045] The 24 organochlorine pesticides are 2,4'-DDT, 4,4'-DDD, 4,4'-DDE, 4,4'-DDT, aldrin, cis-chlordane, trans-chlordane, dicofol, dieldrin, endosulfan sulfate, endrin aldehyde, endrin ketone, endrin, exocyclic heptachlor, heptachlor, hexachlorobenzene, methoxychlor, mirex, α-hexachlorocyclohexane, α-endosulfan, β-endosulfan, β-hexachlorocyclohexane, γ-hexachlorocyclohexane, and δ-hexachlorocyclohexane.

[0046] 2.2 Preparation of matrix-matched standard curve

[0047] Use blank milk sample to dilute the above 1.0 mg / L standard solution into matrix-matched standard curves of 1.0, 5.0, 10.0, 20.0, 50.0, and 100.0 μg / L, and prepare them before use.

[0048] Example 3: Optimization of experimental conditions for lipid dispersion solid phase extraction

[0049] The specific steps of the method for detecting organochlorine pesticides in milk by lipid removal dispersed solid phase extraction of the present invention are as follows:

[0050] (1) Using C8-CsM prepared in Example 1 to remove lipids from milk:

[0051] Extraction: Add NaCl to milk, use n-hexane-acetone to shake and extract organochlorine pesticides, and the supernatant after centrifugation is the milk extract;

[0052] Purification: Add the milk extract into the centrifuge tube containing C8-CsM, vortex to mix, centrifuge, take all the supernatant and blow it to near dryness with nitrogen, re-dissolve it with an organic solvent, and filter to obtain the test solution;

[0053] (2) Detecting the organochlorine pesticides in the test solution obtained in step (2) by GC-HRMS and quantifying by external standard method.

[0054] Based on the above steps, the experimental conditions for detecting 24 organochlorine pesticides were optimized, including the selection of extraction times, the selection of centrifugal speed during extraction, the amount of C8-CsM, the selection of vortex time during purification, and the selection of reconstitution solvent.

[0055] 3.1 Selection of extraction times

[0056] The number of extractions has a certain impact on the recovery rate of trace pesticides in food. The common number of extractions is 1 or 2. Organochlorine pesticides are highly fat-soluble. A mixed solvent of n-hexane and acetone was selected to extract the milk sample with a spiked concentration of 10 μg / kg. The milk extract was extracted once with 10 mL of n-hexane-acetone and twice with 20 mL of n-hexane-acetone to obtain the milk extract. After purification, the test solution was obtained. GC-HRMS was used to detect the organochlorine pesticides in the test solution. The recovery rate was calculated as follows: Figure 3 shown.

[0057] Depend on Figure 3 The results show that extraction once or twice has little effect on the test results. The recovery rates of the same organochlorine pesticides are similar under different extraction times. Therefore, in order to save solvent and shorten the operation time, 10 mL of n-hexane-acetone was used to extract the organochlorine pesticides in milk.

[0058] 3.2 Selection of centrifugal speed during extraction

[0059] NaCl was added to milk, and the milk sample spiked with 10 μg / kg was extracted once with n-hexane-acetone. After mixing, it was centrifuged for 2 min. The centrifugal speeds were 4000 rpm, 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm and 9000 rpm, respectively. The separation effects at different speeds are shown in the figure. Figure 4 shown.

[0060] Depend on Figure 4 The results show that there is basically no separation at 4000rpm for 2min, and it is difficult to obtain more supernatant for lipid dispersed solid phase extraction in the purification process; as the speed increases from 5000rpm to 6000rpm, the thickness of the white solid layer becomes thinner, the supernatant increases, and the separation effect gradually improves; the thickness of the solid layer at 7000rpm, 8000rpm and 9000rpm is basically the same, and the separation effect is equivalent. It can be seen that when the centrifugation time is 2min, in order to obtain a better separation effect, the centrifuge speed should not be lower than 7000rpm.

[0061] 3.3C8-CsM dosage selection

[0062] The amount of adsorbent plays a crucial role in the lipid purification step. C8-CsM with a concentration of 0.2%, 0.4% and 0.6% of the milk mass was used for dispersive solid phase extraction of milk extract with a spike concentration of 10 μg / kg, adsorbing lipids in the milk extract, centrifuging and separating, retaining the organochlorine pesticides to be tested, and obtaining the test solution. The organochlorine pesticides in the obtained test solution were detected by GC-HRMS, and the recovery rate was calculated as follows: Figure 5 shown.

[0063] Depend on Figure 5 The results show that when C8-CsM is not used, the recovery rates of 24 organochlorine pesticides are 24.8-83.9%, which may be due to the matrix inhibition effect of impurities such as lipids, resulting in low recovery rates; when the dosage of C8-CsM is 0.2% of the mass of the milk sample, the recovery rate is 79.1-112.1%, and the recovery rate is significantly improved; when the dosage of C8-CsM is further increased to 0.4% and 0.6% of the mass of the milk sample, the recovery rate of individual pesticides decreases, such as the recovery rate of γ-hexachloride decreased by 20.7%. It can be seen that the use of C8-CsM to purify milk and remove lipids can significantly improve the accuracy of detecting 24 organochlorine pesticides, and when the dosage of C8-CsM is 0.2% of the mass of the milk sample, the detection accuracy is the best.

[0064] 3.4 Selection of vortex time during purification

[0065] Sufficient vortex time can ensure the effective removal of lipids and ensure a high recovery rate of the target organochlorine pesticides. The milk extract with a spike concentration of 10 μg / kg was subjected to dispersed solid phase extraction using C8-CsM at 0.2% of the mass of milk. The vortex time was 1 min, 5 min, and 10 min, respectively. After centrifugation, nitrogen blowing, and filtration, the test solution was obtained. The organochlorine pesticides in the obtained test solution were detected by GC-HRMS, and the recovery rate was calculated as follows: Figure 6 shown.

[0066] Depend on Figure 6 The results show that the recovery rate is 79.1-112.1% when vortexed for 1 minute, 76.9-112.0% when vortexed for 5 minutes, and 76.1-109.5% when vortexed for 10 minutes. The three recovery rates are close. Vortexing for 1-10 minutes can ensure the effective removal of lipids, indicating that C8-CsM can achieve rapid purification of milk extracts and ensure a good recovery rate of organochlorine pesticides.

[0067] 3.5 Choice of reconstitution solvent

[0068] The milk sample spiked with a concentration of 10 μg / kg was extracted, lipid removed, and nitrogen blown, and then re-dissolved with 1 mL of methanol, n-hexane, acetonitrile, acetone, and ethyl acetate, respectively. The test solution was obtained after filtration. The organochlorine pesticides in the obtained test solution were detected by GC-HRMS, and the recovery rate was calculated as follows: Figure 7 shown.

[0069] Depend on Figure 7 The results show that when re-dissolved in methanol, the recovery rate of most compounds is 0, indicating that the solubility of organochlorine pesticides in methanol is low; when re-dissolved in acetonitrile, acetone and ethyl acetate, the recovery rates of 24 organochlorine pesticides are lower than the results when n-hexane is used as the re-dissolution solvent, so n-hexane is used as the re-dissolution solvent.

[0070] Example 4

[0071] Using the C8-CsM prepared in Example 1 as an adsorbent and based on the experimental conditions optimized in Example 3, the specific steps for detecting organochlorine pesticides in milk are as follows:

[0072] Accurately weigh 5.0g of milk, add 2.5g of NaCl and 10mL of n-hexane-acetone, vortex at 3000rpm for 5min, centrifuge at 9000rpm for 2min, take all the supernatant into a centrifuge tube containing 10mg C8-CsM, vortex mix at 3000rpm for 2min, centrifuge at 4000rpm for 2min, blow the obtained supernatant with nitrogen to nearly dryness at 40°C, add 1mL of n-hexane to re-dissolve, filter through 0.22μm filter membrane to obtain the test solution; use GC-HRMS to detect the organochlorine pesticides in the obtained test solution and quantify by external standard method.

[0073] Among them, GC-HRMS instrument conditions: TG-5SilMS chromatographic column (30m×0.25mm×0.25μm); carrier gas: high-purity helium; flow rate: 1.20mL / min; heating method: program heating, 55℃ for 1min, 40℃ / min to 140℃, keep for 5min, 2℃ / min to 210℃, 10℃ / min to 280℃, keep for 5min; injection port temperature: 300℃; injection method: splitless injection; injection volume: 1μL. Mass spectrometry scanning method: Full MS, positive mode; mass number range: 50-500m / z.

[0074] The linearity, spike recovery, precision and accuracy of the above method were evaluated. The linear range of the 24 organochlorine pesticides was 1.0-100.0 μg / L. The peak area y was plotted against the concentration x, and a linear fit was performed to obtain the linear correlation coefficient, as shown in Table 1.

[0075] Table 1 Linear equations and linear correlation coefficients of standard solutions of 24 organochlorine pesticides

[0076]

[0077]

[0078] The above method was verified by a spike recovery test at three concentrations (0.5 μg / kg, 1.0 μg / kg, and 5.0 μg / kg). Six milk samples were measured in parallel for each concentration, and the relative standard deviation (RSD) was calculated to characterize the repeatability of the method. The results are shown in Table 2.

[0079] Table 2 Spike recovery test of milk samples (n=6)

[0080]

[0081]

[0082] As shown in Table 2, the average recovery rate of the above detection method for 24 organochlorine pesticides is 73.9%-110.8%, and the RSD is 0.6%-6.1%, indicating that the instrument precision and method repeatability are good. Taking the lowest spike concentration as the quantitative limit, the quantitative limit of this method for detecting 24 organochlorine pesticides is 0.5μg / kg. The spectrum of the matrix matching standard sample (concentration of 100.0μg / L) of 24 organochlorine pesticides is shown in Figure 8 and Fig. 9 shown.

[0083] Comparative Example 1

[0084] The detection method is basically the same as that of Example 4, except that the chromatographic temperature program is: 40°C for 1.5 min, 25°C / min to 90°C, 1.5 min, 25°C / min to 180°C, 1.5 min, 5°C / min to 280°C, 10°C / min to 300°C, 5 min. The spiked milk sample was analyzed by GC-HRMS. The results are as follows: Fig.10 As shown,

[0085] Depend on Fig.10 It can be seen that under the above chromatographic heating conditions, the chromatographic peak separation of 2,4'-DDT and 4,4'-DDD is low. The gas chromatography heating program has a direct impact on the separation of the target. If the separation of the two compounds is low, it is difficult to achieve accurate quantification. Therefore, the chromatographic heating program of Comparative Example 1 is not suitable for the detection of 24 organochlorine pesticides in this method.

[0086] Comparative Example 2

[0087] The detection method is basically the same as that of Example 4, except that 0.2% of the mass of the milk sample EMR powder is used instead of C8-CsM as the lipid adsorbent, and the spiked concentration is 5.0 μg / kg. The recovery rates of some pesticides by C8-CsM and EMR powder are compared as shown in Table 3 below.

[0088] Table 3 Comparison of recovery rates of some pesticides between C8-CsM and EMR powder

[0089]

[0090] It can be seen from Table 3 above that the recovery rate of C8-CsM for the 9 organochlorine pesticides in Table 3 is better than that of EMR powder, especially the recovery rate of EMR for endrin is only 49.6%, while the recovery rate of C8-CsM for endrin can reach 86.8%; there is no significant difference in the recovery rates of the two for the remaining 15 organochlorine pesticides.

[0091] 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 and improvements made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A method for detecting organochlorine pesticides in milk by lipid removal dispersed solid phase extraction, characterized in that: The steps include: (1) Preparing octanal-modified chitosan copolymer C8-CsM: chitosan powder is dissolved in acetic acid aqueous solution, stirred at room temperature to obtain a chitosan solution, octanal is mixed with ethanol to obtain an octanal ethanol solution, and liquid paraffin and Span80 are added to a round-bottom flask; the chitosan solution and the octanal ethanol solution are slowly added to the round-bottom flask in sequence, emulsified in a constant temperature oil bath, and then a glutaraldehyde crosslinking agent is slowly added. After the reaction, the liquid is cooled to room temperature, centrifuged, washed and dried to obtain C8-CsM; (2) Using the C8-CsM prepared in step (1) to remove lipids from milk: Extraction: Add NaCl to milk, use n-hexane-acetone vortex oscillation to extract organochlorine pesticides, and the supernatant after centrifugation is the milk extract; Purification: Add the milk extract into the centrifuge tube containing C8-CsM, vortex to mix, take all the supernatant after centrifugation, blow it to near dryness with nitrogen, re-dissolve it with an organic solvent, and filter it to obtain the test solution; (3) Detecting the organochlorine pesticides in the test solution obtained in step (2) by GC-HRMS and quantifying by external standard method.

2. The method for detecting organochlorine pesticides in milk according to claim 1, characterized in that: The organic solvent in step (2) is acetonitrile, acetone, ethyl acetate or n-hexane.

3. The method for detecting organochlorine pesticides in milk according to claim 1, characterized in that: The amount of C8-CsM used in step (2) is 0.2-0.6% of the mass of milk.

4. The method for detecting organochlorine pesticides in milk according to claim 1, characterized in that: During the extraction process of step (2), when the centrifugation time is 2 minutes, the centrifugal speed is above 7000 rpm.

5. The method for detecting organochlorine pesticides in milk according to claim 1, characterized in that: During the purification process of step (2), the vortex time is 1-10 min.

6. The method for detecting organochlorine pesticides in milk according to claim 1, characterized in that: The instrument parameters of the GC-HRMS method in step (3) are: TG-5SilMS chromatographic column; Carrier gas: high-purity helium; flow rate: 1.20 mL / min; heating method: programmed heating, injection port temperature: 300°C; injection method: splitless injection; injection volume: 1 μL; mass spectrometry scanning method: Full MS, positive mode; mass number range: 50-500 m / z.

7. The method for detecting organochlorine pesticides in milk according to claim 6, characterized in that: The specific settings of the programmed temperature increase are: hold at 55°C for 1 min, increase to 140°C at 40°C / min, hold for 5 min, increase to 210°C at 2°C / min, increase to 280°C at 10°C / min, hold for 5 min.

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