Method for detecting multiple pesticide residues in corn based on magnetic aminated multi-walled carbon nanotubes

Abstract

The invention belongs to the technical field of detection, and particularly relates to a method for detecting various pesticide residues in corn based on magnetic aminated multi-walled carbon nanotubes. According to the invention, magnetic aminated multi-walled carbon nanotubes (m-M) are prepared from aminated multi-walled carbon nanotubes to serve as a purification material to improve a QuEChERS method, and meanwhile, the method for detecting multiple pesticide residues in corn is established by combining with UPLC-MS / MS (Ultra Performance Liquid Chromatography-Mass Spectrometry / Mass Spectrometry). The method has the advantages of high recovery rate, simplicity in operation, high precision and high accuracy, and 45 pesticide residues in corn can be simultaneously analyzed. Compared with a traditional QuEChERS purification material, the m-M can achieve an ideal purification effect without being combined with other purification materials, solid-liquid rapid separation can be achieved by applying an external magnetic field, purified liquid is obtained, the operation time is saved, the analysis efficiency is improved, and the method is suitable for rapid detection of a large number of samples.

Description

Technical Field

[0001] The present invention belongs to the field of detection technology. Specifically, the present invention relates to a method for detecting various pesticide residues in corn based on magnetically aminated multi-walled carbon nanotubes. Background Art

[0002] Corn is one of the world's major food crops, which is widely planted and has high yields worldwide. In the process of food production, it is inevitable to be harmed by pests and diseases. Commonly used prevention and control methods generally include breeding of pest-resistant varieties, chemical control, biological control, etc., but the most widely used, fast and efficient prevention and control method is still chemical control - pesticide control. Large amounts of pesticides used and low utilization rates may lead to excessive pesticide residues in corn, affecting the quality of agricultural products and endangering human health. Pesticide residue detection can effectively prevent foods with excessive pesticide residues from entering the market.

[0003] The rapid sample preparation method (QuEChERS) for agricultural product testing was proposed by Anastassiades et al., a scientist from the United States Department of Agriculture (USDA) in 2003. It has been developed for more than 20 years. It is fast, easy to operate, cheap, efficient, durable and safe. It is the preferred method for multi-pesticide residue detection today. Pesticide residue detection is generally divided into three parts: extraction, purification and detection. The performance of the QuEChERS method depends on the ability of the selected purification material to adsorb impurities. Traditional QuEChERS purification materials, such as N-propylethylenediamine (PSA), octadecylsilane bonded silica gel (C18), graphitized carbon black (GCB), etc., often need to be used in combination to achieve a good purification effect, and the supernatant needs to be obtained by centrifugation for detection, which makes the sample pretreatment process cumbersome and time-consuming, which is not conducive to the rapid detection of a large number of samples. Therefore, it is very meaningful to develop a material with simple preparation method and strong purification performance to improve the QuEChERS method, so that it is simpler to operate, has a shorter processing time and higher efficiency when used for the detection of multi-pesticide residues in crops such as corn. Summary of the invention

[0004] The purpose of the present invention is to develop a method for rapid processing and detection of multiple pesticide residues. After long-term research, the present invention has developed a method for detecting multiple pesticide residues in corn based on magnetic amino multi-walled carbon nanotubes, thereby achieving the purpose of the present invention. Specifically, the scheme of the present invention is as follows:

[0005] A method for detecting multiple pesticide residues in corn based on magnetically aminated multi-walled carbon nanotubes comprises the following steps:

[0006] (1) Preparation of corn sample extract to be tested

[0007] (2) Synthetic purification material mM

[0008] (3) Purify the sample extract to obtain a purified solution

[0009] (4) The purified liquid filter membrane was subjected to qualitative and quantitative analysis using UPLC-MS / MS.

[0010] In one embodiment, corn is crushed by a multifunctional crusher and then passed through a 40-mesh standard sieve to serve as a corn sample to be tested.

[0011] In one embodiment, 1000 g of corn is randomly sampled, ground with a multifunctional grinder, passed through a 40-mesh standard sieve, and placed in a polyethylene bag as a corn sample, which is stored at -20°C for later use.

[0012] In one embodiment, ultrapure water is added to the corn sample, vortexed to mix, and allowed to stand. Then, an acetic acid-acetonitrile solution is added, vortexed, NaCl and anhydrous MgSO4 are added, vortexed to extract, and the supernatant is obtained by centrifugation to obtain a corn sample extraction solution.

[0013] In one embodiment, 5 g of corn sample is accurately weighed into a 50 mL polytetrafluoroethylene centrifuge tube, 10 mL of ultrapure water is added, vortexed to mix, and allowed to stand for 30 min, followed by adding 10 mL of 1% acetic acid-acetonitrile solution (V:V=1:99), vortexed at 3000 rpm for 3 min, then adding 4 g of NaCl and 1 g of anhydrous MgSO4, vortexed at 3000 rpm for 1 min, and finally centrifuged at 4200 rpm for 5 min, taking the supernatant to obtain a corn sample extraction solution.

[0014] In one embodiment, the aminated multi-walled carbon nanotubes are ultrasonically dispersed in an ethylene glycol solution, and then ferric chloride hexahydrate and sodium acetate are added, and ultrasonication is continued. After the ultrasonication is completed, stirring is continued for a period of time, and then the solution is transferred to a hydrothermal synthesis reactor lined with polytetrafluoroethylene, and reacted at high temperature. After the reaction is completed, it is cooled to room temperature, and an external magnetic field is applied for solid-liquid separation. The obtained solid is washed alternately with water and ethanol several times, and vacuum dried to obtain the purified material mM (magnetic aminated multi-walled carbon nanotubes).

[0015] In one embodiment, 50.0 mg of amino-modified multi-walled carbon nanotubes (MWNTs-NH2) are accurately weighed and ultrasonically dispersed in 30 mL of ethylene glycol solution, then 0.1352 g of ferric chloride hexahydrate and 0.2051 g of sodium acetate are weighed and added to the above solution, and ultrasonication is continued for 20 minutes. After the end, stirring is performed for 30 minutes, and the solution is transferred to a hydrothermal synthesis reactor lined with polytetrafluoroethylene, and the reaction is carried out at 200°C for 8 hours. After the reaction is completed, the reaction is cooled to room temperature, and an external magnetic field is applied for solid-liquid separation. The obtained solid is washed alternately with water and ethanol for 3 times each, and vacuum dried at 60°C for 12 hours to obtain the purified material mM (magnetic amino-modified multi-walled carbon nanotubes).

[0016] In one embodiment, the corn sample extract is mixed with magnetic amino-modified multi-walled carbon nanotubes, vortexed at high speed, and then an external magnetic field is applied to separate the solid and liquid, and the supernatant is collected to obtain a purified solution.

[0017] In one embodiment, 1 mL of the prepared corn sample extract was taken into a 5 mL centrifuge tube filled with mM, and then vortexed at 3000 rpm for 1 min, and then an external magnetic field was applied to separate the solid and liquid, and the obtained supernatant was the purified liquid.

[0018] In one embodiment, the purified solution is filtered through a 0.22 μm organic filter membrane and placed in a sample injection vial for UPLC-MS / MS analysis.

[0019] In one embodiment, the ratio of mM to extract is 40:1 mg / mL.

[0020] In one embodiment, the UPLC-MS / MS analysis conditions in step (4) are as follows: Chromatographic conditions: the chromatographic column is ACQUITY BEH C18, 2.1mm×50mm, particle size 1.7μm; flow rate 0.3mL / min; injection volume 5μL; column temperature 40℃; mobile phase A 0.1% formic acid water, phase B 0.1% formic acid acetonitrile, mobile phase gradient:

[0021]

[0022]

[0023] That is, the mobile phase gradient is: 0-0.5min, 95% by volume of phase A, 5% by volume of phase B; 0.5-2min, 95%-10% by volume of phase A, 5%-90% by volume of phase B; 2min-7min, 10% by volume of phase A; 90% by volume of phase B; 7min-7.1min, 10%-95% by volume of phase A, 90%-5% by volume of phase B; 7.1min-8min, 95% by volume of phase A, 5% by volume of phase B.

[0024] Mass spectrometry analysis conditions: Waters UPLC-xevo TQMS; ion source is ESI source; scanning mode is positive ion scanning; monitoring mode is multiple reaction monitoring (MRM) mode; capillary voltage is 3.0KV; backflush gas flow rate is 50L / Hr; desolvation gas flow rate is 900L / Hr; desolvation gas temperature is 500℃; collision gas flow rate is 0.15mL / min; ion source temperature is 150℃.

[0025] In one embodiment, the pesticide is: Tricyclazole, Myclobutanil, Triadimefon, Tebuconazole, Hexaconazole, Metconazole, Epoxiconazole, Propiconazole, Azoxystrobin, Trifloxystrobin, Isoprocarb, Imidacloprid, Dinotefuran, Thiamethoxam, Acetamiprid, Thiacloprid, Pirimicarb ), Pyriproxyfen, Indoxacarb, Simazine, Simetryn, Atrazine, Prometryn, Isoproturon, Propanil, Diuron, Fluroxypyr, Acetochlor, Alachlor, Pretilachlor, Butachlor, Clodinafop-propargyl, Pendimethalin, Fluoxastrobin, icosulfuron, Bensulfuron methyl), Difenoconazole, Pyraclostrobin, Flonicamid, Metolachlor, Mefenacet, Florasulam, Metamifop, Penoxsulam, Mesosulfuron-methyl.

[0026] In one embodiment, the present invention further discloses 10. a kit for detecting various pesticide residues in corn based on magnetically aminated multi-walled carbon nanotubes, characterized in that the kit contains magnetically aminated multi-walled carbon nanotubes.

[0027] Beneficial Effects

[0028] The present invention establishes a method for detecting multiple pesticide residues in corn based on magnetic aminated multi-walled carbon nanotubes. This method uses magnetic aminated multi-walled carbon nanotubes (mM) as purification materials to improve the QuEChERS method, and combines it with UPLC-MS / MS to establish a method for detecting multiple pesticide residues in corn. The advantages of this method are high recovery rate, simple operation, high precision and accuracy, and the ability to simultaneously analyze 45 pesticide residues in corn. Compared with traditional QuEChERS purification materials, mM can achieve an ideal purification effect without combining with other purification materials, and can achieve rapid solid-liquid separation by applying an external magnetic field to obtain a purified liquid, saving operation time, improving analysis efficiency, and being suitable for rapid detection of a large number of samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 :mM preparation flow chart;

[0030] Figure 2 :mM characterization diagram (A: FTIR, B: XRD, C: VSM, D: SEM, E: TEM);

[0031] Figure 3 : Recovery rates of 45 pesticides under different extraction solvents;

[0032] Figure 4 : Recovery rates of 45 pesticides under different extraction solvent volumes;

[0033] Figure 5 : Recovery rates of 45 pesticides at different extraction times;

[0034] Figure 6 : Recovery rates of 45 pesticides at different mM dosages;

[0035] Figure 7 :Comparison of matrix effects before and after purification; DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. The equipment and reagents used in the embodiments and test examples can be obtained from commercial sources unless otherwise specified. Unless otherwise specified, the reagents used in the present invention are all analytical grade reagents. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Embodiment 1:

[0038] 1. Materials and Methods

[0039] 1.1 Corn samples

[0040] The corn samples were purchased organic corn, which was screened to be free of pesticide residues. 1000 g of corn samples were randomly selected, crushed with a multifunctional crusher, passed through a 40-mesh standard sieve, put into a polyethylene bag, and stored at -20°C for later use.

[0041] 1.2 Pesticide standards

[0042] There are 45 pesticides in total, namely Tricyclazole, Myclobutanil, Triadimefo n, Tebuconazole, Hexaconazole, Metconazole, Epoxiconazole, Propiconazole, Azoxystrobin, Trifloxystrobin, Isoprocarb, Imidacloprid, Dinotefuran, Thiamethoxam, Acetamiprid, and id), Thiacloprid, Pirimicarb, Pyriproxyfen, Indoxacarb, Simazine, Simetryn, Atrazine, Prometryn, Isoproturo n, Propanil, Diuron, Fluroxypyr, Acetochlor, Alachlor, Pretilachlor, Butachlor, Clodinafop-propargyl, Pen dimethalin, Fluoxastrobin, icosulfuron, Bensulfuron methy l), Difenoconazole, Pyraclostrobin, Flonicamid, Metolachlor, Mefenacet, Florasulam, Metami fop, Penoxsulam, Mesosulfuron-methyl, purity ≥ 95%, all commercially available. Aminated multi-walled carbon nanotubes (10-20nm, Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.).

[0043] 1.3 Preparation method of magnetic amino multi-walled carbon nanotubes (mM)

[0044] Accurately weigh 50.0 mg MWNTs-NH2 and ultrasonically disperse it in 30 mL ethylene glycol solution. Then weigh 0.1352 g ferric chloride hexahydrate and 0.2051 g sodium acetate and add them to the above solution. Continue ultrasonicating for 20 min. After stirring for 30 min, transfer the solution to a hydrothermal synthesis reactor lined with polytetrafluoroethylene and react at 200 °C for 8 h. After the reaction is completed, cool to room temperature and apply an external magnetic field for solid-liquid separation. The obtained solid is washed alternately with water and ethanol for 3 times each, and vacuum dried at 60 °C for 12 h to obtain mM, which is placed in a brown glass bottle and stored at room temperature for use.

[0045] 1.4 Characterization of magnetic amino-modified multi-walled carbon nanotubes (mM)

[0046] The molecular structure of the material is determined by FTIR; the morphological structure of the material is characterized by SEM; the crystal structure of the material is characterized by XRD; and the magnetic properties of the material are characterized by VSM.

[0047] 1.5 Preparation of standard solution

[0048] 1.5.1 Preparation of standard solution

[0049] Accurately weigh 10 mg of each pesticide standard and place it in a 10 mL volumetric flask. Use acetonitrile to make up to 10 mL to obtain a 1000 mg / L standard solution of each pesticide. Store at -20°C away from light.

[0050] 1.5.2 Mixed standard solution

[0051] Accurately pipette 100 μL of each pesticide standard solution into a 10 mL volumetric flask and dilute to the mark with acetonitrile to obtain a 10 mg / L mixed standard solution.

[0052] 1.5.3 Solvent standard working curve and matrix matching standard working curve

[0053] First, a certain amount of mixed standard solution was taken and added to a certain amount of 1% acetic acid-acetonitrile solution (V:V=1:99) to prepare a 1 mg / L working solution, and then the 1 mg / L working solution was diluted step by step with 1% acetic acid-acetonitrile solution to 0.005, 0.01, 0.05, 0.1, 0.2, 0.5 mg / L solvent standard working curve; corn blank matrix extract was used to match the 1 mg / L working solution to 0.005, 0.01, 0.05, 0.1, 0.2, 0.5 mg / L matrix standard working curve. The working curves were prepared and used immediately.

[0054] 1.6 Sample pretreatment

[0055] Accurately weigh 5g corn sample in a 50mL polytetrafluoroethylene centrifuge tube, add 10mL ultrapure water, vortex mix, let stand for 30min, then add 10mL 1% acetic acid-acetonitrile solution (V:V=1:99), vortex at 3000rpm for 3min, then add 4gNaCl, 1g anhydrous MgSO4, vortex at 3000rpm for 1min, finally centrifuge at 4200rpm for 5min, take the supernatant, and obtain the corn sample extraction solution. Take 1mL of corn sample extract in a 5mL centrifuge tube containing 40mg mM, then vortex at 3000rpm for 1min, then apply an external magnetic field to separate solid-liquid, take the supernatant, and obtain the purified solution, then pass the purified solution through a 0.22μm organic filter membrane in a sampling vial for UPLC-MS / MS analysis.

[0056] 1.7 UPLC-MS / MS analysis parameters

[0057] Chromatographic conditions: The chromatographic column is ACQUITY UPLC BEH C18, 2.1mm×50mm, particle size 1.7μm; flow rate 0.3mL / min; injection volume 5μL; column temperature 40°C; mobile phase A 0.1% formic acid water, phase B 0.1% formic acid acetonitrile, mobile phase gradient see Table 1 below.

[0058] Table 1: Mobile phase gradient

[0059] Time / min A / ％ B / ％ 0 95 5 0.50 95 5 2.00 10 90 7.00 10 90 7.10 95 5 8.00 95 5

[0060] Mass spectrometry analysis conditions: Waters UPLC-xevo TQMS; ESI source; positive ion scan; multiple reaction monitoring (MRM) mode; capillary voltage 3.0 KV; backflush gas flow rate 50 L / Hr; desolvation gas flow rate 900 L / Hr; desolvation gas temperature 500 °C; collision gas flow rate 0.15 mL / min; ion source temperature 150 °C. The mass spectrometry parameters of 45 pesticides are shown in Table 2.

[0061] Table 2: Pesticide mass spectrometry parameters

[0062]

[0063]

[0064]

[0065] “a” is the quantitative ion

[0066] 1.8 Matrix Effects

[0067] The matrix effect can intuitively evaluate the purification performance of purification materials. The matrix refers to the components in the sample extract other than the target analyte, and these components often interfere with the response signal of the target analyte, resulting in an increase or decrease in the response signal. This phenomenon is called the matrix effect (ME). In this invention, the post-extraction addition method is used to calculate the matrix effect. Standard working curves are prepared using 1% acetonitrile in acetic acid, corn extract, and purified corn extract as solvents respectively. The matrix effect is calculated using the following formula:

[0068] The matrix effect ME1 of corn extract = B / A × 100%

[0069] The matrix effect ME2 of purified corn extract = C / A × 100%

[0070] In the formula, A is the slope of the standard curve of a certain pesticide in pure solvent; B is the slope of the matrix standard curve of the pesticide prepared with corn extract as the solvent; C is the slope of the matrix standard curve of the pesticide prepared with purified corn extract as the solvent; 0.8 < ME < 1.2 indicates a weak matrix effect, and the matrix effect can be ignored, indicating good purification effect; ME < 0.8 indicates a matrix inhibition effect, and the smaller the value, the stronger the inhibition effect; ME > 1.2 indicates a matrix enhancement effect, and the larger the value, the greater the matrix enhancement effect.

[0071] 1.9 Recovery rate

[0072] The mass fraction ω is used to represent the residual amount of each pesticide in the sample.

[0073] Recovery rates of each pesticide:

[0074] In the formula, C1 represents the mass concentration of the analyte in the purified matrix-matched standard working solution, with the unit of mg / L; A represents the peak area of the mass chromatogram of the analyte in the sample solution; V represents the volume of the extract, with the unit of mL; As represents the peak area of the mass chromatogram of the analyte in the purified matrix-matched standard working solution; m represents the mass of the sample, with the unit of g; C0 represents the theoretical addition concentration, with the unit of mg / kg.

[0075] 2. Results and analysis

[0076] 2.1 m-M characterization results

[0077] As shown in the Fourier transform infrared spectroscopy (FTIR) graph ( Figure 2 A), the absorption peak at 593 cm -1 is the absorption peak of Fe-O-Fe, proving the existence of Fe3O4. The stretching vibration peaks of N-H and C-N are at 1629 and 1039 respectively, the non-stretching vibration peak of C-H is at 2919, and the in-plane bending vibration of C-H is at 1382, proving the existence of MWNTs-NH2. As Figure 2As shown in B, the X-ray diffraction (XRD) diagram reveals the crystal structure of the material. MWNTs-NH2 and Fe3O4 have two crystal structures. The main diffraction peaks at 30.3°, 35.7°, 57.4°, and 62.9° correspond to the crystal planes (220), (311), (511), and (440), which are consistent with the characteristic crystal planes of the XRD standard card of ferroferric oxide. Figure 2 As shown in the C vibrating sample magnetometer curve (VSM) graph, at room temperature, the mM hysteresis loop is basically a curve, the coercive force is close to 0, there is almost no hysteresis, showing good superparamagnetism, and the saturation magnetization intensity reaches 17.17 Gauss. Figure 2 Medium D and Figure 2 As shown in Figure E, the morphology and structure of mM were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and it can be clearly seen that the magnetic spheres are attached to the tubular structure. In summary, mM was successfully prepared and has the characteristics of both MWNTs-NH2 and Fe3O4.

[0078] 2.2 QuEChERS method optimization

[0079] 2.2.1 Selection of extraction conditions

[0080] The pretreatment of pesticide residue analysis is generally divided into two steps: extraction and purification. Among them, extraction is the step of extracting the target pesticide from the sample with a solvent, and its efficiency is directly related to the accuracy of the pesticide residue analysis results. This experiment optimized the type of extraction solvent, extraction solvent volume and extraction time. Figure 3 , 4 As shown in Figures 5 and 5 , at the added concentration of 1 mg / kg, when the extraction solvent was 1% acetic acid-acetonitrile solution (V:V=1:99), the volume was 10 mL, and vortexed at 3000 rpm for 3 min, all 45 target pesticides were extracted, and the recovery rates were between 70.96% and 103.50%.

[0081] 2.2.2 Optimization of m-M dosage

[0082] MWNTs-NH2 has a high specific surface area, high strength, large pore capacity, and its surface is modified with organic chains and has active amino groups, which can effectively remove pigments, metal ions, organic acids, alcohols, phenols and other substances. However, while MWNTs-NH2 effectively adsorbs the matrix, it also adsorbs the target compound, so the dosage of MWNTs-NH2 needs to be optimized. Figure 6As shown in the figure, when the dosage of mM is between 10-30 mg, only 38 pesticides have a recovery rate between 70% and 110%; when the dosage of mM is 40 mg, the recovery rates of 45 target pesticides are between 70.23% and 108.32%, and when the dosage of mM is 50 mg, mM will adsorb some target pesticides, causing the recovery rate of target pesticides to be lower than 70%. In summary, the dosage of mM is finally determined to be 40 mg / mL, that is, the ratio of mM to corn extract is 40:1.

[0083] 3. Matrix Effects

[0084] The matrix effect is an important basis for evaluating the performance of purification materials. The present invention prepares the standard working curve of the unpurified corn matrix matching and the standard working curve of the purified corn matrix matching according to the above method. Figure 7 As shown in the figure, all 45 target pesticides have matrix inhibition effects, ranging from 0.05 to 0.84, of which 1 target pesticide has a weak matrix effect, 17 target pesticides have a medium matrix effect, and 27 have a strong matrix effect; after purification by mM, the matrix effects are all weakened, ranging from 0.17 to 1.09, of which 4 pesticides have a weak matrix effect, 27 target pesticides have a medium matrix effect, and 14 target pesticides have a strong matrix effect. In summary, mM has good purification performance.

[0085] 4. Methodological Validation

[0086] 4.1 Linearity, detection limit and quantification limit of the method

[0087] This method uses matrix-matched standard working solution to compensate for matrix effects to improve the accuracy of the test results. Use the purified blank sample solution to accurately prepare mixed standard solutions of 0.005, 0.01, 0.05, 0.1 and 0.5 mg / L. Use mass concentration as the horizontal axis and target pesticide peak area as the vertical axis to draw standard curves. The standard curves of 45 target pesticides are shown in Table 3. In the range of 0.005-0.5 mg / L, 44 target pesticides such as tricyclazole have good linear relationships, R 2 The linear relationship of fluroxypyr was good in the range of 0.01-0.5 mg / L. 2 The detection limit (LOD) of 44 targets such as tricyclazole was 0.005 mg / kg, the quantification limit (LOQ) was 0.01 mg / kg, and the LOD of fluroxypyr was 0.01 mg / kg, and the LOQ was 0.05 mg / kg.

[0088] Table 3: Standard curves and correlation coefficients (R 2 ), detection limit and quantification limit

[0089]

[0090]

[0091]

[0092] 4.2 Accuracy and precision of the method

[0093] In order to verify the accuracy and precision of this method, this experiment set three concentration addition levels of low, medium and high in blank corn samples. The results are shown in Table 4. When the addition level was 0.01 mg / kg, the recovery rate of 44 pesticides such as tricyclazole was 65.68%-119.01%, and the relative standard deviation (RSD) was 0.69%-9.66%; when the addition level was 0.1 mg / kg, the recovery rate was 80.80%-119.68%, and the RSD was 0.59%-8.78%; when the addition level was 1 mg / kg, the recovery rate was 70.23%-108.32%, and the RSD was 0.23%-7.56%. The recoveries of fluroxypyr at the addition levels of 0.05, 0.1 and 1 mg / kg were 116.75%, 111.36% and 102.33%, respectively, and the RSDs were 1.14%, 5.97% and 7.36%, respectively.

[0094] Table 4 Recoveries and RSDs of 44 pesticides in corn matrix at three addition levels

[0095]

[0096]

[0097]

[0098] 5. Actual sample testing

[0099] The preferred method of the present invention was applied to test corn samples purchased from Shangqiu, Henan, Changchun, Jilin, Suzhou, Anhui, Yancheng, Jiangsu and Baoding, Hebei. The content of target pesticides in the samples was calculated by matching the standard curve with the corn matrix. The test results are shown in the following table.

[0100]

[0101]

[0102]

[0103] ND: Not detected.

[0104] In summary, the mM prepared by the present invention is used as a purification material in the QuEChERS method. Compared with other traditional purification materials, it can achieve a good purification effect without combining with other purification materials, has a fast separation speed (no centrifugation, an external magnetic field can be used for separation), and is simple to operate. This method uses the improved QuEChERS method as a sample pretreatment method, combined with UPLC-MS / MS analysis technology, to establish a method for detecting multiple pesticide residues in corn. This method has a high recovery rate, simple operation, high precision and accuracy, and can simultaneously analyze 45 pesticide residues in corn, and is suitable for rapid detection of a large number of samples.

[0105] The above content is a further detailed description of the present invention in combination with specific implementation methods. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the scope of protection determined by the claims submitted for the present invention.

Claims

1. A method for detecting multiple pesticide residues in corn based on magnetically aminated multi-walled carbon nanotubes, characterized in that: The method comprises the following steps: (1) Preparing the extract of the corn sample to be tested; (2) Synthesize purification material mM (magnetic amino multi-walled carbon nanotubes); (3) purifying the sample extract to obtain a purified solution; (4) The purified liquid filter membrane was qualitatively and quantitatively analyzed using UPLC-MS / MS.

2. The method according to claim 1, characterized in that: The step (1) is to add ultrapure water to the corn sample, vortex mix, let stand, then add acetic acid-acetonitrile solution, vortex, then add NaCl and anhydrous MgSO4, vortex extract, centrifuge to obtain the supernatant, and obtain the corn sample extraction solution.

3. The method according to claim 1, characterized in that The step (2) comprises ultrasonically dispersing the aminated multi-walled carbon nanotubes in an ethylene glycol solution, then adding ferric chloride hexahydrate and sodium acetate, continuing ultrasonication, continuing stirring for a period of time after the ultrasonication ends, and then transferring the solution to a hydrothermal synthesis reactor lined with polytetrafluoroethylene, reacting at high temperature, cooling to room temperature after the reaction ends, applying an external magnetic field for solid-liquid separation, and washing the obtained solid with water and ethanol alternately for several times, and vacuum drying to obtain the purified material mM (magnetic aminated multi-walled carbon nanotubes).

4. The method according to claim 1, characterized in that: The high temperature reaction is carried out at 200° C. for 8 hours.

5. The method according to claim 1, characterized in that The step (3) is to mix the corn sample extract with the magnetic amino-modified multi-walled carbon nanotubes, vortex at high speed, and then apply an external magnetic field to separate the solid and liquid, and take the supernatant to obtain the purified solution.

6. The method according to claim 5, characterized in that The ratio of magnetic amino multi-walled carbon nanotubes to corn extract was 40:1, mg / mL.

7. The method according to claim 1, characterized in that In the UPLC-MS / MS analysis, the chromatographic conditions are as follows: the chromatographic column is ACQUITY UPLC® BEH C18, 2.1 mm×50 mm, and the particle size is 1.7 μm; the flow rate is 0.3 mL / min; the injection volume is 5 μL; the column temperature is 40°C; the mobile phase A is 0.1% formic acid in water, the mobile phase B is 0.1% formic acid in acetonitrile, and the mobile phase gradient is: 0-0.5 min, 95% by volume of phase A, 5% by volume of phase B; 0.5-2 min, 95%-10% by volume of phase A, 5%-90% by volume of phase B; 2 min-7 min, 10% by volume of phase A; 90% by volume of phase B; 7 min-7.1 min, 10%-95% by volume of phase A, 90%-5% by volume of phase B; 7.1 min-8 min, 95% by volume of phase A, 5% by volume of phase B.

8. The method according to claim 1, characterized in that In the UPLC-MS / MS analysis, the mass spectrometry analysis conditions were: Waters UPLC-xevo TQMS; the ion source was an ESI source; the scanning mode was a positive ion scan; the monitoring mode was a multiple reaction monitoring (MRM) mode; the capillary voltage was 3.0 KV; the backflush gas flow rate was 50 L / Hr; the desolvation gas flow rate was 900 L / Hr; the desolvation gas temperature was 500 °C; the collision gas flow rate was 0.15 mL / min; and the ion source temperature was 150 °C.

9. The method according to claim 1, characterized in that The multiple pesticides are: Tricyclazole, Myclobutanil, Triadimefon, Tebuconazole, Hexaconazole, Metconazole, Epoxiconazole, Propiconazole, Azoxystrobin, Trifloxystrobin, Isoprocarb, Imidacloprid, Dinotefuran, Thiamethoxam, Acetamiprid, Thiacloprid, Pirimicarb, Pyridoxine, Pyriproxyfen, Indoxacarb, Simazine, Simetryn, Atrazine, Prometryn, Isoproturon, Propanil, Diuron, Fluroxypyr, Acetochlor, Alachlor, Pretilachlor, Butachlor, Clodinafop-propargyl, Pendimethalin, Fluoxastrobin, icosulfuron, Bensulfuron methyl), Difenoconazole, Pyraclostrobin, Flonicamid, Metolachlor, Mefenacet, Florasulam, Metamifop, Penoxsulam, Mesosulfuron-methyl.

10. A kit for detecting various pesticide residues in corn based on magnetically aminated multi-walled carbon nanotubes, characterized in that: The kit contains magnetic amino-modified multi-walled carbon nanotubes.

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