Magnetic fluid and application thereof in sample pretreatment and pyrethroid pesticide detection

Abstract

The invention belongs to the technical field of pesticide residue detection, and particularly relates to a magnetic fluid and application thereof in sample pretreatment and pyrethroid pesticide detection. The magnetic fluid provided by the invention comprises a hydrophobic eutecticevaporate solvent and magnetic nanoparticles dispersed in the hydrophobic eutecticevaporate solvent, wherein the hydrophobic eutecticevaporate solvent comprises coumarin serving as a hydrogen bond donor and thymol serving as a hydrogen bond acceptor. Through the hydrophobic interaction between the magnetic hydrophobic deep-eutectic solvent and the hydrophobic pyrethroid pesticide and the strong pi-pi action between benzene ring structures of coumarin and thymol and benzene rings of the pyrethroid pesticide, the extraction efficiency of the magnetic fluid on the pyrethroid pesticide is improved; the detection sensitivity and the detection accuracy of the pyrethroid pesticide can be improved; the magnetic nanoparticles are added, so that the magnetic fluid can realize phase separation by adopting an external magnetic field, the operation is simple and rapid, and the detection process of pyrethroid pesticide residues is simplified.

Description

Technical Field

[0001] The invention relates to the technical field of pesticide residue detection, and in particular to a magnetic fluid and its application in sample pretreatment and pyrethroid pesticide detection. Background Art

[0002] Pyrethroid insecticides (PY) are the main insecticide category in the world. They are highly effective, low-toxic, low-residue, and easy to degrade. They are widely used in agricultural pest control, as well as in the control of sanitary pests and storage pests. At the same time, the problem of PY residues in the environment and agricultural products is becoming increasingly serious, causing serious harm to the ecological environment and human health, and also reducing the quality of agricultural products. More than 10 PY pesticides have been detected in my country, mainly including cypermethrin, deltamethrin, bifenthrin, cypervalerate, cypermethrin, permethrin, cyhalothrin, cyfluthrin, beta-cypermethrin, and phenothrin.

[0003] In recent years, several pretreatment strategies have been developed for preconcentration of pesticide residues, including solid phase extraction (SPE), magnetic solid phase extraction (MSPE), dispersive liquid-liquid microextraction (DLLME), liquid-liquid microextraction (LLME), etc. For example, a Chinese patent with authorization announcement number CN110231423B, which was authorized on April 22, 2022, discloses a method for determining pyrethroid pesticides in grain by dispersed liquid-liquid microextraction-high performance liquid chromatography. Thymol (thymol) or choline chloride is used as a hydrogen bond acceptor, and pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid or decanoic acid is used as a hydrogen bond donor. The hydrophobic low eutectic solvent formed by the mixture is used as an extractant, and is added to the supernatant obtained by vortex mixing the sample to be tested and the dispersant, and dispersed liquid-liquid microextraction is carried out. After the extraction, the extract is centrifuged and ice-bathed, and the extracted phase is converted into a solid phase and then collected, and melted into a liquid at room temperature to obtain a solution of the sample to be tested. This method uses a hydrophobic low eutectic solvent for extraction, avoids the use of harmful organic solvents, reduces the adverse effects and damage to the ecological environment, and is more green and environmentally friendly. However, the extraction efficiency of pyrethroid pesticides using the hydrophobic low eutectic solvent in the above method is low, resulting in low sensitivity and accuracy of subsequent detection; and after extraction, the extraction phase needs to be converted into a solid phase using an ice bath and then collected, which makes the phase separation operation complicated.

[0004] On June 6, 2024, Li et al. published a new type of ferrofluid in the article "Novel ferrofluid based on hydrophobic deepeutectic solvents for separation and analysis of trace estrogens in environmental water and urine samples". The ferrofluid was prepared using a hydrophobic deep eutectic solvent (DES) and a Fe3O4@graphite composite material. It was used as a green microextraction medium for separating and enriching trace estrogens in actual samples. It can quickly process and accurately determine three estrogens (estradiol [E2], estriol [E3], and ethinyl estradiol [EE2]) in environmental water and urine samples, avoiding the use of volatile toxic organic extraction solvents and cumbersome phase separation operations. However, the above ferrofluid is aimed at the enrichment and separation of estrogen, and the extraction and detection analysis of pyrethroid pesticides are not disclosed. Summary of the invention

[0005] The object of the present invention is to provide a magnetic fluid to solve the problem of low extraction efficiency of pyrethroid pesticides by existing magnetic fluids.

[0006] The second object of the present invention is to provide an application of a magnetic fluid in sample pretreatment during pyrethroid pesticide detection, so as to solve the problem of low extraction efficiency of pyrethroid pesticides by existing magnetic fluids.

[0007] The third object of the present invention is to provide an application of a magnetic fluid in the detection of pyrethroid pesticides to solve the problems of low detection accuracy and low detection sensitivity of pyrethroid pesticides.

[0008] In order to solve the above technical problems, the technical solution of the magnetic fluid of the present invention is:

[0009] A magnetic fluid comprises a hydrophobic deep eutectic solvent and magnetic nanoparticles dispersed in the hydrophobic deep eutectic solvent. The hydrophobic deep eutectic solvent comprises coumarin as a hydrogen bond donor and thymol as a hydrogen bond acceptor.

[0010] The present invention improves the prior art and provides a magnetic fluid comprising a hydrophobic low eutectic solvent and magnetic nanoparticles. The hydrophobic low eutectic solvent uses coumarin as a hydrogen bond donor and thymol as a hydrogen bond acceptor. Through the hydrophobic interaction between the hydrophobic low eutectic solvent and the hydrophobic pyrethroid pesticide, the benzene ring structure of coumarin and thymol in the hydrophobic low eutectic solvent and the benzene ring of the pyrethroid pesticide have a strong π-π interaction. The two work together to achieve selective and efficient enrichment of pyrethroid pesticides, greatly improve the extraction efficiency of the magnetic fluid for pyrethroid pesticides, and help further improve the detection sensitivity and detection accuracy of pyrethroid pesticides. In addition, the addition of the magnetic nanoparticles enables the magnetic fluid to achieve phase separation using an external magnetic field, and the operation is simple and fast, which greatly simplifies the detection process of pyrethroid pesticide residues, saves a lot of time and reduces costs.

[0011] In order to further improve the extraction efficiency, preferably, the molar ratio of coumarin to thymol is 1:(1-4). The hydrophobic low eutectic solvent is coumarin and thymol stirred at 80-100°C until transparent and clear. More preferably, the molar ratio of coumarin to thymol is 1:(1-3). More preferably, the molar ratio of coumarin to thymol is 1:(2-2.5).

[0012] In order to further improve the uniformity of the dispersion of magnetic nanoparticles in the hydrophobic low eutectic solvent and improve the stability of the magnetic fluid, preferably, the magnetic nanoparticles are oleic acid-coated Fe3O4 nanoparticles, and the oleic acid-coated Fe3O4 nanoparticles are obtained by hydrothermal reaction of iron salt, anhydrous sodium acetate and oleic acid, and the temperature of the hydrothermal reaction is 190-210°C, and the time of the hydrothermal reaction is 5-10 hours. Coating oleic acid on the surface of Fe3O4 nanoparticles can reduce the surface tension of the hydrophobic low eutectic solvent on Fe3O4 nanoparticles, which is convenient for the uniform dispersion of nanoparticles and the stability of the fluid.

[0013] In order to further improve the stability of the magnetic fluid, preferably, the ratio of the volume of the hydrophobic deep eutectic solvent to the mass of the magnetic nanoparticles is (1-2) mL: (50-100) mg. The magnetic fluid under this ratio has good stability, has a selective and efficient enrichment effect on pyrethroid pesticide residues in agricultural products, and can be conveniently used for the analysis and detection of pyrethroid pesticide residues in agricultural products.

[0014] In order to further improve the stability of the magnetic fluid, preferably, the magnetic fluid is obtained by mixing magnetic nanoparticles and a hydrophobic low eutectic solvent and then ultrasonically treating the mixture; the ultrasonic treatment time is 20 to 40 minutes.

[0015] The technical solution of the application of the magnetic fluid of the present invention in sample pretreatment during pyrethroid pesticide detection is as follows:

[0016] The invention discloses an application of a magnetic fluid in sample pretreatment during pyrethroid pesticide detection, comprising the following steps: mixing a sample extract and the magnetic fluid for liquid-liquid microextraction, separating the magnetic fluid under the action of an external magnetic field after the extraction is completed, and obtaining a sample solution to be tested after elution.

[0017] The magnetic fluid provided by the present invention is used in sample pretreatment during pyrethroid pesticide detection. The magnetic fluid is used as an extractant to extract the pyrethroid pesticides. The hydrophobic interaction and strong π-π interaction between the hydrophobic low eutectic solvent in the magnetic fluid and the pyrethroid pesticides are utilized. The two work together to achieve selective and efficient enrichment of the pyrethroid pesticides, thereby improving the extraction efficiency of the pyrethroid pesticides. The magnetic particles in the magnetic fluid are used to achieve phase separation after extraction, which is beneficial to the rapid processing and accurate determination of the pyrethroid pesticides in the sample.

[0018] In order to further enhance the hydrophobic interaction between the hydrophobic deep eutectic solvent and the pyrethroid pesticide, preferably, an inorganic salt is added during mixing, and (0.05-0.5) g of inorganic salt is added for every 5 mL of sample extract. The addition of inorganic salt is beneficial to increase the ionic strength, enhance the hydrophobic interaction between the hydrophobic deep eutectic solvent and the pyrethroid pesticide, and thus improve the extraction efficiency. The inorganic salt is sodium chloride.

[0019] In order to further improve the extraction efficiency, preferably, (25-100) μL of magnetic fluid is added to every 5 mL of sample extract.

[0020] In order to further improve the extraction efficiency, preferably, the liquid-liquid microextraction is performed by vortex oscillation, and the extraction time is 3 to 5 minutes.

[0021] In order to further improve the elution efficiency, preferably, the elution is performed by adding dichloromethane for 3 to 5 minutes. The elution is performed by adding dichloromethane for vortex elution for 3 to 5 minutes.

[0022] In order to further improve the adsorption efficiency, preferably, the pyrethroid pesticides include tefluthrin, bioresmethrin, bifenthrin, cypermethrin, λ-cyhalothrin, trans-permethrin, cis-permethrin, cyhalothrin, cypermethrin, high-efficiency cypermethrin, flucythrin, etherpyrethrin, fluvalinate, cypermethrin, S-cypermethrin, and deltamethrin.

[0023] The technical solution for the application of the magnetic fluid of the present invention in the detection of pyrethroid pesticides is as follows:

[0024] The invention discloses an application of magnetic fluid in the detection of pyrethroid pesticides, comprising the following steps: pre-treating a sample by using the application method of magnetic fluid in sample pre-treatment during the detection of pyrethroid pesticides to obtain a sample solution to be tested, and performing detection and analysis by using GC-MS / MS.

[0025] The magnetic fluid of the present invention is used in the detection of pyrethroid pesticides. The magnetic fluid is used to pre-treat the sample, and the hydrophobic interaction and strong π-π interaction between the hydrophobic low eutectic solvent in the magnetic fluid and the pyrethroid pesticide are used to improve the extraction efficiency of the pyrethroid pesticide, thereby improving the detection sensitivity and detection accuracy of the pyrethroid pesticide, and the magnetic particles in the magnetic fluid are used to achieve phase separation after extraction. The operation is simple and fast, which greatly simplifies the detection process of pyrethroid pesticide residues, saves a lot of time and reduces costs, and provides a detection method for quickly processing and accurately determining pyrethroid pesticides in samples.

[0026] The detection method of the present invention can simultaneously determine 16 representative pyrethroid pesticides in agricultural products, expanding the detection range of pyrethroid pesticides. The detection limit of the 16 pyrethroid pesticides is 0.41-7.22 ng / mL, and the quantitative limit is 1.37-26.37 ng / mL.

[0027] In order to further improve the detection sensitivity and accuracy, preferably, the chromatographic conditions during GC-MS / MS detection and analysis are as follows: the chromatographic column is an Agilent DB-5MS chromatographic column; the heating program is: 40-50°C for 1-2 min, then heated to 250-270°C at 30-40°C / min, then heated to 280-290°C at 6-8°C / min, then heated to 300-320°C at 10-12°C / min, and maintained for 5-8 min; injection port temperature: 280-290°C; injection mode: splitless injection; injection volume: 1-2 μL.

[0028] In order to further improve the detection sensitivity and accuracy, preferably, the mass spectrometry conditions during GC-MS / MS detection and analysis are: electron bombardment source: 70-80eV; ion source temperature: 280-290°C; transfer line temperature: 280-290°C; solvent delay: 3-4min; scanning mode: positive ion scanning; detection mode: multiple reaction monitoring. The above chromatographic mass spectrometry parameters are conducive to separating each target analyte and improving the sensitivity of detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the composition structure of the magnetic fluid of Example 1 of the present invention;

[0030] Figure 2This is a flow chart of the application of magnetic fluid in the detection of pyrethroid pesticides according to Example 3 of the present invention;

[0031] Figure 3 A bar graph showing the extraction efficiency of magnetic fluids formed by hydrophobic deep eutectic solvents of different compositions. DETAILED DESCRIPTION

[0032] The technical concept of the magnetic fluid of the present invention is as follows:

[0033] Among the existing hydrophobic low eutectic solvents, only the benzene ring structure of thymol interacts with the benzene ring of pyrethroid pesticides through π-π interaction, which makes the selective adsorption capacity of hydrophobic low eutectic solvents for pyrethroid pesticides limited, and the phase separation after extraction of the existing hydrophobic low eutectic solvents is complex; and the existing ferromagnetic fluids are only for the enrichment and separation of estrogen, and lack a rapid and efficient extraction method for pyrethroid pesticides.

[0034] The present invention adopts a magnetic fluid including a hydrophobic low eutectic solvent and magnetic nanoparticles dispersed in the hydrophobic low eutectic solvent. Thymol and coumarin both containing benzene ring structures in the hydrophobic low eutectic solvent form a stronger π-π interaction with the benzene ring of the pyrethroid pesticide, thereby improving the selective adsorption capacity of the hydrophobic low eutectic solvent for the pyrethroid pesticide. The magnetic nanoparticles are conducive to phase separation, thereby constructing a rapid and efficient extraction method for pyrethroid pesticides.

[0035] Magnetic fluid is a colloidal suspension in which magnetic nanoparticles are composed of ferromagnetic materials such as iron, cobalt, nickel or their oxides. Compared with traditional liquid microextraction solvents, magnetic fluids are diverse in variety and more designable, and can simultaneously play the role of magnetic nanoparticles and hydrophobic low eutectic solvents during application.

[0036] The magnetic fluid of the present invention is used in sample pretreatment during pyrethroid pesticide detection. The specific method is: mixing a sample extract, a magnetic fluid and an inorganic salt, performing liquid-liquid microextraction by vortex oscillation, separating the magnetic fluid by an external magnet after the extraction is completed, adding dichloromethane for vortex elution, and obtaining a sample solution to be tested.

[0037] In a specific embodiment, the sample extract is the supernatant obtained by centrifugation after the sample is extracted with water. When the sample is a solid powder, the sample extract is the supernatant obtained by mixing the solid powder and water, ultrasonicating, standing and centrifuging; (1-3) mL of water is added for every 10 mg of solid powder; the ultrasonication time is 30-60 min; the standing time is 30-60 min; the centrifugation speed is 3000-5000 rpm, and the centrifugation time is 5-10 min. When the sample is a fruit and vegetable sample, the sample extract includes a first supernatant obtained by centrifugation after homogenization of the fruit and vegetable sample, and a second supernatant obtained by mixing and centrifuging the solid residue after homogenization and centrifugation and water; the sample extract is obtained by filtering the first supernatant and the second supernatant with a 0.45-0.50 μm water membrane; (1-5) mL of water is added for every 10 mg of solid phase residue.

[0038] In a specific embodiment, the hydrophobic deep eutectic solvent is obtained by stirring coumarin and thymol at 80-100° C. for 30-60 minutes.

[0039] In a specific embodiment, after vortex elution, the sample solution to be tested is filtered through a 0.22-0.45 μm organic phase membrane.

[0040] In a specific embodiment, the oleic acid-coated Fe3O4 nanoparticles are obtained by hydrothermal reaction of iron salt, anhydrous sodium acetate and oleic acid in a solvent; the iron salt is FeCl3·6H2O; the molar ratio of FeCl3·6H2O, anhydrous sodium acetate and oleic acid is (0.10-0.15): (0.90-1.0): (0.090-0.095).

[0041] 1. Specific embodiments of the magnetic fluid of the present invention

[0042] Example 1

[0043] The magnetic fluid of this embodiment is composed of 1 mL of a hydrophobic low eutectic solvent (HDES) and 100 mg of oleic acid-coated Fe3O4 nanoparticles (Fe3O4-OA) dispersed in the hydrophobic low eutectic solvent. The hydrophobic low eutectic solvent is composed of coumarin (HBA) as a hydrogen bond donor and thymol (HBD) as a hydrogen bond acceptor. The molar ratio of coumarin to thymol is 1:2. The composition structure diagram of the magnetic fluid is shown in FIG. Figure 1 shown.

[0044] The preparation method of oleic acid-coated Fe3O4 nanoparticles is as follows:

[0045] Weigh 4.0 g of FeCl3·6H2O into a 500 mL three-necked flask, add 120 mL of ethylene glycol and stir mechanically (350 r) in a 50°C water bath to dissolve it (5 min), then add 8.0 g of anhydrous sodium acetate and 3 mL of oleic acid (0.89 g / cm 3 ), continue to stir vigorously (350r) for 0.5h to obtain a uniform solution; transfer the uniform solution to a hydrothermal reactor and react at 200℃ for 6h; transfer all the liquid after the reaction to a beaker, separate it with a magnet, and discard the upper solution; wash it with deionized water and anhydrous ethanol for 3-5 times (the added volume is 40mL), vortex oscillation for 5min each time, and then dry it in a vacuum drying oven at 50℃ for 12h.

[0046] Preparation of hydrophobic deep eutectic solvent: Coumarin and thymol in a molar ratio of 1:2 were magnetically stirred at 80°C for 30 min to obtain a clear and transparent solution.

[0047] Preparation of magnetic fluid: 100 mg of Fe3O4-OA was added into 1 mL of HDES as magnetic nanoparticles and ultrasonicated for 20 min to disperse the nanoparticles and form a stable magnetic fluid.

[0048] In other embodiments, the molar ratio of coumarin to thymol is 1:1, 1:3, 1:4, respectively.

[0049] II. Specific Examples of Application of the Magnetic Fluid of the Present Invention in Sample Pretreatment for Pyrethroid Pesticide Detection Example 2

[0050] The application of the magnetic fluid of this embodiment in sample pretreatment during pyrethroid pesticide detection is as follows:

[0051] 1) Tobacco leaf sample pretreatment: weigh 100 mg of tobacco leaf powder into a 50 mL centrifuge tube, add 10 mL of water and sonicate for 30 min, let stand for 30 min, centrifuge at 3000 rpm for 5 min in a centrifuge, and use the supernatant after solid-liquid separation as the sample extract for later use.

[0052] 2) Liquid-liquid microextraction: 5 mL of sample extract was added to a 12 mL glass bottle, 0.2 g of NaCl was added, and then the magnetic fluid (90 μL) of Example 1 was poured into the glass bottle, and the mixture was vigorously shaken for 3.5 min under the action of a vortex agitator. After the extraction was completed, an external magnet was used to achieve phase separation, and finally 1 mL of dichloromethane solution was added for vortex elution. The eluate was obtained by vortex elution for 3 min, and 500 μL of the eluate was filtered through a 0.22 μm organic phase membrane to obtain a sample solution to be tested.

[0053] In other embodiments, when the sample is a fruit or vegetable sample, the fruit or vegetable sample pretreatment method is as follows:

[0054] The fruits and vegetables were chopped and homogenized in a homogenizer. 50.0 g of homogenized fruit and vegetable samples were weighed and placed in 50 mL centrifuge tubes. The samples were centrifuged at 3000 rpm for 5 min. The first supernatant was obtained after solid-liquid separation and transferred to a beaker. The solid phase residue obtained after solid-liquid separation was mixed with 5 mL of water at a rate of 50 mg, and the second supernatant was obtained after centrifugation. The first supernatant and the second supernatant were mixed and filtered through a 0.45 μm water membrane to obtain the fruit and vegetable sample extract, which was transferred to a 100 mL volumetric flask and fixed to volume for later use.

[0055] 3. Specific Examples of Application of the Magnetic Fluid of the Present Invention in Detection of Pyrethroid Pesticides

[0056] Example 3

[0057] The flow chart of the application of magnetic fluid in the detection of pyrethroid pesticides in this embodiment is shown in FIG. Figure 2 As shown, the specific method is as follows:

[0058] The sample was pretreated using the method for applying the magnetic fluid in Example 2 in sample pretreatment for pyrethroid pesticide detection to obtain a sample solution to be tested, which was then detected and analyzed using GC-MS / MS.

[0059] The GC-MS / MS detection and analysis method is: use the internal standard method to establish a standard working curve for each target compound, enter the sample solution to be tested into the GC-MS / MS instrument for analysis, substitute the detection data into the standard working curve, and calculate the concentrations of tefluthrin, bioresmethrin, bifenthrin, cypermethrin, λ-cyhalothrin, trans-permethrin, cis-permethrin, cyhalothrin, cypermethrin, high-efficiency cypermethrin, flucythrin, ethomethrin, fluvalinate, cypermethrin, S-cypermethrin, and deltamethrin in the sample.

[0060] The chromatographic conditions for GC-MS / MS detection and analysis are as follows: the chromatographic column is an Agilent DB-5MS chromatographic column (60m×250μm×0.25μm); the heating program is: maintain at 40°C for 1 min, then increase the temperature to 250°C at 30°C / min, then increase the temperature to 280°C at 6°C / min, and then increase the temperature to 300°C at 10°C / min, and maintain for 5 min; injection port temperature: 280°C; injection mode: splitless injection; injection volume: 1μL; carrier gas: helium, purity ≥99.999%, flow rate 1.0mL / min.

[0061] The mass spectrometry conditions for GC-MS / MS analysis were as follows: electron bombardment source: 70 eV; ion source temperature: 280°C; transfer line temperature: 280°C; solvent delay: 3 min; scan mode: positive ion scan; detection mode: multiple reaction monitoring (MRM), see Table 1.

[0062] Table 1 Quantitative ion pairs, qualitative ion pairs, dwell time, collision voltage of each compound

[0063]

[0064]

[0065] Note: a: quantitative ion, b: qualitative ion.

[0066] IV. Experimental Examples

[0067] Experimental Example 1

[0068] In this experimental example, the detection method of Example 3 was used to detect pyrethroid pesticides in tobacco leaf samples. The linear equations, correlation coefficients, detection limits and quantification limits of various pyrethroid pesticide residues with 3 times the signal-to-noise ratio (S / N) as the detection limit and 10 times the S / N as the quantification limit are shown in Table 2.

[0069] Table 2 Linear equations, correlation coefficients, detection limits and quantification limits of pyrethroid pesticide residues

[0070]

[0071]

[0072] As can be seen from Table 2, the detection limit of the detection method of the present invention for 16 pyrethroid pesticides is 0.41-7.22 ng / mL, and the quantification limit is 1.37-26.37 ng / mL.

[0073] The same sample was measured six times in parallel within one day and for five days. The relative standard deviation (RSD) of the measurement results indicated the intra-day precision and inter-day precision of the method. At the same time, the spike recovery tests at low, medium and high spike levels were performed. The test results are shown in Table 3.

[0074] Table 3 Intra-day precision, inter-day precision and spike recovery test results

[0075]

[0076]

[0077] It can be seen from the results in Table 3 that the detection method provided by the present invention has good precision and high spike recovery rate, and is suitable for the detection of pyrethroid pesticide residues in agricultural products.

[0078] 16 pyrethroid pesticides were extracted and tested using a magnetic fluid formed by a hydrophobic low eutectic solvent (HDES) of different components. The extraction test method was referred to Example 3. The extraction efficiency was evaluated by the spiked recovery rate obtained by GC-MS / MS test. The spiked recovery rate = [(X1-X0) / m]*100%, where X1 is the measured value of the spiked sample, X0 is the measured value of the sample, and m is the spiked amount. The extraction efficiency bar graph is as follows: Figure 3 As shown, COU-THY represents the HDES formed by coumarin-thymol, THY-MEN represents the HDES formed by thymol-DL-menthol, MEN-DEC represents the HDES formed by DL-menthol-decanoic acid, and THY-DEC represents the HDES formed by thymol-decanoic acid. Figure 3 It can be seen that the low eutectic solvents formed by coumarin and thymol (1:1-4) in different molar ratios all show good extraction efficiency, among which the molar ratio of 1:2 shows better extraction efficiency.

[0079] Experimental Example 2

[0080] Five kinds of agricultural product samples (tobacco leaves, cabbage, lettuce, celery, and apple) were collected, and the detection method in Example 3 was used to perform liquid phase microextraction and GC-MS / MS analysis on tefluthrin, bioresmethrin, bifenthrin, cypermethrin, λ-cyhalothrin, trans-permethrin, cis-permethrin, cyhalothrin, cypermethrin, beta-cypermethrin, flucythrin, ethomethrin, fluvalinate, cypermethrin, S-cypermethrin, and deltamethrin in the agricultural product samples. The results are shown in Table 4.

[0081] Table 4 Actual content and spiked recovery test results of pyrethroid pesticides in 5 agricultural product samples

[0082]

[0083]

[0084] The detection method provided by the present invention can conveniently detect the content of tefluthrin, bioresmethrin, bifenthrin, cypermethrin, λ-cyhalothrin, trans-permethrin, cis-permethrin, cyhalothrin, cypermethrin, high-efficiency cypermethrin, flucythrin, ethomethrin, fluvalinate, cypermethrin, S-cypermethrin and deltamethrin in agricultural products, and the detection process is simple, and the detection precision and stability are good.

[0085] In Table 4, λ-cyhalothrin and ethomethrin were detected in tobacco leaves, and bifenthrin was detected in lettuce and celery. In addition, deltamethrin was also detected in lettuce. The detection method provided by the present invention achieved a high recovery rate in the application of agricultural product samples, indicating that the use of the magnetic fluid liquid-liquid microextraction technology provided by the present invention can lay a good foundation for the subsequent research on pyrethroid pesticide residues.

[0086] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A magnetic fluid, characterized in that: The magnetic fluid comprises a hydrophobic deep eutectic solvent and magnetic nanoparticles dispersed in the hydrophobic deep eutectic solvent. The hydrophobic deep eutectic solvent comprises coumarin as a hydrogen bond donor and thymol as a hydrogen bond acceptor.

2. The magnetic fluid according to claim 1, characterized in that: The molar ratio of coumarin to thymol is 1:(1-4).

3. The magnetic fluid according to claim 1, characterized in that: The magnetic nanoparticles are oleic acid-coated Fe3O4 nanoparticles, which are obtained by hydrothermal reaction of iron salt, anhydrous sodium acetate and oleic acid. The temperature of the hydrothermal reaction is 190-210° C., and the time of the hydrothermal reaction is 5-10 hours.

4. The magnetic fluid according to any one of claims 1 to 3, characterized in that: The ratio of the volume of the hydrophobic low eutectic solvent to the mass of the magnetic nanoparticles is (1-2) mL: (50-100) mg.

5. The magnetic fluid according to claim 1, characterized in that: The magnetic fluid is obtained by mixing magnetic nanoparticles and a hydrophobic low eutectic solvent and then ultrasonically treating the mixture; the ultrasonic time is 20 to 40 minutes.

6. An application of the magnetic fluid according to any one of claims 1 to 5 in sample pretreatment for pyrethroid pesticide detection, characterized in that: The method comprises the following steps: mixing the sample extract and the magnetic fluid for liquid-liquid microextraction, separating the magnetic fluid under the action of an external magnetic field after the extraction is completed, and obtaining a sample solution to be tested after elution.

7. The use of the magnetic fluid as claimed in claim 6 in sample pretreatment for pyrethroid pesticide detection, characterized in that: Add inorganic salt during mixing, adding (0.05~0.5) g of inorganic salt for every 5 mL of sample extract.

8. The use of the magnetic fluid as claimed in claim 6 in sample pretreatment for pyrethroid pesticide detection, characterized in that: For every 5 mL of sample extract, add (25-100) μL of magnetic fluid.

9. The use of the magnetic fluid as claimed in claim 6 in sample pretreatment for pyrethroid pesticide detection, characterized in that: The liquid-liquid microextraction is performed by vortex oscillation, and the extraction time is 3 to 5 minutes.

10. The use of the magnetic fluid as claimed in claim 6 in sample pretreatment for pyrethroid pesticide detection, characterized in that: The elution is performed by adding dichloromethane, and the elution time is 3 to 5 minutes.

11. The use of the magnetic fluid as claimed in claim 6 in sample pretreatment for pyrethroid pesticide detection, characterized in that: The pyrethroid pesticides include tefluthrin, bioresmethrin, bifenthrin, cypermethrin, λ-cyhalothrin, trans-permethrin, cis-permethrin, cyhalothrin, cypermethrin, high-efficiency cypermethrin, flucythrin, ethomethrin, fluvalinate, cypermethrin, S-cypermethrin, and deltamethrin.

12. Use of the magnetic fluid according to any one of claims 1 to 5 in the detection of pyrethroid pesticides, characterized in that: The method comprises the following steps: pre-treating the sample by using the method for applying the magnetic fluid in any one of claims 6 to 11 in sample pre-treatment during pyrethroid pesticide detection to obtain a sample solution to be tested, and performing detection and analysis by using GC-MS / MS.

13. The use of the magnetic fluid in the detection of pyrethroid pesticides as claimed in claim 12, characterized in that: The chromatographic conditions for GC-MS / MS analysis were as follows: the chromatographic column was an Agilent DB-5MS column; the temperature program was: 40-50°C for 1-2 min, then increased to 250-270°C at 30-40°C / min, then increased to 280-290°C at 6-8°C / min, then increased to 300-320°C at 10-12°C / min, and maintained for 5-8 min; injection port temperature: 280-290°C; injection mode: splitless injection; injection volume: 1-2 µL.

14. The use of the magnetic fluid in the detection of pyrethroid pesticides as claimed in claim 12, characterized in that: The mass spectrometry conditions for GC-MS / MS analysis were as follows: electron bombardment source: 70~80 eV; ion source temperature: 280~290℃; transfer line temperature: 280~290℃; solvent delay: 3~4 min; scanning mode: positive ion scanning; detection mode: multiple reaction monitoring.

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