Covalent organic framework-based composite beads and application thereof in detection of neonicotinoid pesticides

Abstract

The application discloses a kind of composite beads based on covalent organic framework and its application in neonicotinoid pesticide detection, belong to analytical detection technical field.The preparation of the composite beads CACPs of the present application includes as follows: TAPB, DMTA is dissolved in the mixed solution of mesitylene and 1,4-dioxane, add aqueous acetic acid, stirring reaction at room temperature, after reaction, collect the precipitate, obtain yellow TAPB-DMTA powder;Then it is dissolved in sodium alginate solution, form TAPB-DMTA-sodium alginate mixed solution, then it is added dropwise to receiving solution, after solidification and shaping, the composite beads CACPs are obtained;Based on the composite beads CACPs, solid-liquid separation and recycling of adsorbent in dSPE process can be realized quickly and simply, when used for neonicotinoid pesticide detection, it has the advantages of high sensitivity and accuracy, simple operation, less organic reagent, and has practical application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of composite beads based on covalent organic framework and its application in neonicotinoid pesticide detection, belong to analytical detection technical field. BACKGROUND

[0002] Neonicotinoid pesticides are the fastest growing and most widely used class of insecticides, due to their extensive use in the environment, strong polarity and good water solubility, easy to be absorbed by plant tissues after application, leading to their persistence in soil and surface water, and can further accumulate in domestic water and crops through the cycle in the environment. At present, the multi-media residues of neonicotinoid insecticides and the resulting sharp decline in species diversity have attracted global attention. Studies have shown that the regional high mortality of bees is related to the large-scale use of neonicotinoids, and exposure to neonicotinoids poses potential risks to mammals and even humans, including reproductive toxicity, neurotoxicity, hepatotoxicity / liver cancer toxicity, immunotoxicity, genetic toxicity, etc.

[0003] Due to its high risk to biodiversity and human health, it is of great significance to detect neonicotinoid pesticide residues in food. However, due to their low concentration levels in actual samples and complex sample matrix, it is difficult to directly determine them. Therefore, it is necessary to pretreat before instrument detection to reduce the interference of impurities and enrich them.

[0004] The pretreatment methods of neonicotinoid pesticides reported in the prior art mainly include thin film microextraction (TFME), dispersive liquid-liquid microextraction (DLLME), dispersive solid-phase extraction (dSPE), solid-phase extraction (SPE), quick, easy, cheap, effective, rugged, and safe (QuEChERS), and magnetic solid-phase extraction (MSPE). Among them, dSPE has the advantages of less consumption of organic solvent, low cost, simple operation, high recovery rate, etc., and thus has wide application prospect. However, the adsorption material plays a crucial role in the dSPE process.

[0005] Covalent organic framework (COF) is a kind of porous crystalline polymer composed of light elements (such as hydrogen, carbon, oxygen, nitrogen and boron), which has the advantages of large specific surface area, adjustable pore size, good thermal stability and easy functionalization. However, due to the nanoscale size and low density of COF, it is difficult to separate completely by centrifugation during dSPE, and at least 10 minutes of centrifugation is required, which may cause secondary environmental pollution. At the same time, due to the strong hydrophobicity of COF, it is not conducive to the adsorption of polar substances to a certain extent. At present, there are studies that use polymers (such as polyvinylidene fluoride, polyacrylonitrile, polyethyleneimine and alginate) as nanoadsorbent carriers to synthesize different forms of three-dimensional macroscopic materials (hydrogel, nanofilm) with improved properties, which show good potential in adsorption and separation of trace pollutants, so this composite strategy can be introduced into the field of sample pretreatment, and developing more targeted composite materials based on COF is the key to widening the application range of COF-dSPE. In order to apply the composite strategy to simply and effectively extract neonicotinoid pesticides in complex food matrix, it is urgent to develop a composite adsorbent based on COF with good adsorption effect on neonicotinoid pesticides. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides a kind of COF-sodium alginate-Ca 2+ -PAA composite beads (CACPs) based on TAPB-DMTA, and provides a method (CACPs-dSPE) for dispersing solid phase extraction of polar neonicotinoid pesticides using the CACPs as a hydrophilic adsorbent. The method can detect five neonicotinoid pesticides (dinotefuran, clothianidin, imidacloprid, thiamethoxam and acetamiprid) in food samples, and has the advantages of high sensitivity, simple operation, low organic reagent consumption and practical application prospect.

[0007] The first object of the present application is to provide a preparation method of CACPs based on covalent organic framework-sodium alginate-Ca 2+ -PAA polymer composite beads, which comprises the following steps:

[0008] (1) synthesis of TAPB-DMTA

[0009] 1,3,5-tris (4-aminophenyl) benzene (TAPB) and 2,5-dimethoxy terephthaldehyde (DMTA) are dissolved in a mixed solution of mesitylene and 1,4-dioxane, then an aqueous acetic acid solution is added, and the reaction is stirred at room temperature. After the reaction is completed, the precipitate is separated and collected, washed and dried to obtain yellow TAPB-DMTA powder;

[0010] (2) preparation of CACPs

[0011] The TAPB-DMTA powder prepared in step (1) is dissolved in sodium alginate solution to form a TAPB-DMTA-sodium alginate mixed solution. Then the mixed solution is added dropwise to CaCl2-polyacrylic acid (PAA) receiving solution. Magnetic stirring is used to assist in full solidification. After shaping, the mixed beads are collected, washed, and freeze-dried to obtain composite beads CACPs.

[0012] In one embodiment, the molar ratio of TAPB and DMTA in step (1) is 1:2 to 2:3.

[0013] In one embodiment, the volume ratio of mesitylene and 1,4-dioxane in the mixed solution of mesitylene and 1,4-dioxane in step (1) is 1:1.

[0014] In one embodiment, the concentration of the acetic acid aqueous solution in step (1) is 3–5 mol·L⁻¹. -1 .

[0015] In one embodiment, the stirring reaction in step (1) is carried out at room temperature (24-30°C) for 36-72 hours.

[0016] In one embodiment, the washing in step (1) is performed using a methanol solution.

[0017] In one embodiment, the drying in step (1) is vacuum drying overnight at 40–60°C.

[0018] In one embodiment, the concentration of TAPB-DMTA in the TAPB-DMTA-sodium alginate mixed solution in step (2) is 5–50 mg / mL. -1 Preferred 25 mg / mL -1 .

[0019] In one embodiment, the CaCl2-polyacrylic acid (PAA) receiving solution in step (2) specifically refers to a solution prepared by dissolving anhydrous CaCl2 in polyacrylic acid.

[0020] In one embodiment, step (2) involves receiving Ca in the solution. 2+ Concentration of 3–9 mg / mL -1 Preferred concentration: 6 mg / mL -1 .

[0021] In one embodiment, the PAA concentration in the receiving solution in step (2) is 0.005–0.03 mol / L. -1 The preferred concentration is 0.01 mol / L. -1 .

[0022] In one embodiment, the dropping of the mixed solution into the CaCl2-polyacrylic acid (PAA) receiving solution in step (2) is specifically referring to the use of a pipette to control the dropping amount, and the volume of the pipette tip is 20 μL-5 mL; preferably 1 mL.

[0023] In one embodiment, the solidification time in step (2) is 2-5 min.

[0024] In one embodiment, the drying in step (2) is freeze-drying for 12-36 h.

[0025] The second object of the present application is to provide an adsorbent for dispersive solid phase extraction, which is composed of the composite beads CACPs prepared by the above-mentioned method.

[0026] In one embodiment, the adsorbent is composed of 1-18 composite beads CACPs; preferably 18 composite beads CACPs.

[0027] The third object of the present application is to provide a method for detecting neonicotinoid pesticides based on the above-mentioned adsorbent for dispersive solid phase extraction, which comprises:

[0028] adding the adsorbent for dispersive solid phase extraction into a sample solution to be detected, performing dispersive solid phase extraction, taking out the adsorbent after the extraction, and removing the residual solution on the surface of the adsorbent with a blotting paper; then eluting the adsorbent to obtain an eluent, passing the eluent through a membrane, and performing HPLC-PDA detection, and calculating the content of neonicotinoid pesticides in the sample to be detected according to a standard curve model.

[0029] In one embodiment, the pH value of the sample solution to be detected is 3-9; preferably the pH value is 6.

[0030] In one embodiment, no salt solution is added in the extraction solution during the dispersive solid phase extraction.

[0031] In one embodiment, the extraction time is 5-60 min; preferably 40 min.

[0032] In one embodiment, the extraction temperature is 24-30℃.

[0033] In one embodiment, the elution solvent is methanol, and the elution volume is 0.5 mL.

[0034] In one embodiment, the elution time is 2.5-25 min; preferably 15 min.

[0035] In one embodiment, the specific conditions of the HPLC-PDA detection are as follows: a chromatographic column C18 (5 μm, 4.6 x 250 mm); mobile phase was acetonitrile and water (25:75, v:v) at a flow rate of 1 mL min -1 at 25℃, for 12 min, and the detection wavelengths were 270 nm (dinotefuran, clothianidin, imidacloprid), 246 nm (acetamiprid), and 253 nm (thiamethoxam).

[0036] A fourth object of the present application is to provide the use of the above-mentioned method for detecting neonicotinoid pesticides in food detection.

[0037] The beneficial effects of the present application are:

[0038] (1) The hydrophilic composite beads CACPs of the present application have good adsorption and extraction capacity for polar neonicotinoid pesticides, and the dSPE process can be quickly and simply realized based on the dispersion solid phase extraction (dSPE) of CACPs, which has the advantages of high sensitivity, simple operation, and less use of organic reagents;

[0039] (2) The sample treated based on CACPs-dSPE is detected: the linear range is 0.01-1 μg mL -1 and 1-10 μg mL -1 , R 2 is 0.9963-0.9997, the limit of quantification (LOQs) is 0.01 μg mL -1 , and the limit of detection (LODs) is 0.0043-0.0059 μg mL -1 . When applied to actual fruit and vegetable samples (peach, pear, lettuce, cucumber, and tomato), the standard recovery rate is 73.6%-116.2%, and the standard deviation (RSD) is less than 9.9%; the detection result has high accuracy, and has a wide practical application prospect for the detection of neonicotinoid pesticides in fruit and vegetable samples. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a schematic diagram of the experimental process of the present application; (A) is a synthesis route diagram of TAPB-DMTA in Example 1; (B) is a preparation flowchart of CACPs; (C) is a dSPE flowchart;

[0041] Figure 2 are scanning electron micrographs of TAPB-DMTA and CACPs prepared in Example 1 and sodium alginate-Ca 2+ -PAA polymer composite beads (ACPs); (A-B) are TAPB-DMTA; (C-D) are ACPs; (E-F) are CACPs;

[0042] Figure 3Fourier transform infrared spectra of TAPB-DMTA and CACPs prepared in Example 1; (A) is TAPB-DMTA; (B) is CACPs;

[0043] Figure 4 X-ray diffraction pattern of TAPB-DMTA prepared in Example 1;

[0044] Figure 5 Thermogravimetric analysis curves of TAPB-DMTA, ACPs and CACPs prepared in Example 1;

[0045] Figure 6 X-ray photoelectron spectroscopy of CACPs prepared in Example 1;

[0046] Figure 7 Nitrogen adsorption-desorption isotherm of CACPs prepared in Example 1;

[0047] Figure 8 Comparison chart of the effect of different Ca 2+ concentrations on the extraction efficiency of CACPs;

[0048] Figure 9 Comparison chart of the effect of different PAA concentrations on the extraction efficiency of CACPs;

[0049] Figure 10 Comparison chart of the effect of different TAPB-DMTA concentrations on the extraction efficiency of CACPs;

[0050] Figure 11 Comparison chart of the effect of different CACPs sizes on the extraction efficiency of CACPs;

[0051] Figure 12 Comparison chart of the effect of different pH on the extraction efficiency of CACPs;

[0052] Figure 13 Comparison chart of the effect of different salt concentrations (NaCl) on the extraction efficiency of CACPs;

[0053] Figure 14 Comparison chart of the effect of different extraction times on the extraction efficiency of CACPs;

[0054] Figure 15 Comparison chart of the effect of different CACPs amounts on the extraction efficiency of CACPs;

[0055] Figure 16 Comparison chart of the effect of different elution solvents on the extraction efficiency of CACPs;

[0056] Figure 17 This is a comparison graph showing the effect of different elution solvent volumes on the extraction efficiency of CACPs in Example 5;

[0057] Figure 18 This is a comparison graph showing the effect of different elution times on the extraction efficiency of CACPs in Example 5;

[0058] Figure 19 This is a graph showing the number of times CACPs were reused in Example 5;

[0059] Figure 20 Comparative data graphs of the extraction effects of composite beads prepared for different COFs on neonicotinoid pesticides and comparative data graphs of the extraction effects of CACPs on different pesticides; (A) data graph of the extraction effects of different COFs on neonicotinoid pesticides; (B) data graph of the extraction effects of CACPs on different pesticides. Detailed Implementation

[0060] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0061] Example 1

[0062] A covalent organic framework - sodium alginate-Ca 2+ The preparation method of PAA polymer composite beads (CACPs) includes the following steps:

[0063] (1) Synthesis of TAPB-DMTA

[0064] 1,3,5-Tris(4-aminophenyl)benzene (TAPB, 112.46 mg, 0.32 mmol) and 2,5-dimethoxyterephthalaldehyde (DMTA, 93.20 mg, 0.48 mmol) were dissolved in 6 mL of a mixed solution of mesitylene and 1,4-dioxane (v:v = 1:1). The solution was sonicated at room temperature until homogeneous, and then 1 mL of 3 mol·L⁻¹ solution was added dropwise. -1 The acetic acid aqueous solution was stirred at room temperature for 72 h; then washed three times with methanol, the precipitate was collected by centrifugation, and dried under vacuum at 60 °C overnight to obtain yellow powder TAPB-DMTA.

[0065] (2) Preparation of CACPs

[0066] Add 25 mg of TAPB-DMTA prepared in step (1) to 1 mL of 20 mg mL -1 The sodium alginate solution was ultrasonically dispersed to form a COF-sodium alginate mixed solution; simultaneously, 120 mg of anhydrous CaCl2 was dissolved in 20 mL of 0.01 mol / L solution. -1A receiving solution was prepared in polyacrylic acid (PAA). Using a 1 mL pipette tip, a COF-sodium alginate mixture was added dropwise to the receiving solution. Magnetic stirring was used to assist in complete solidification. After shaping, the mixed beads were collected, washed with ultrapure water, and freeze-dried for 24 hours to obtain a covalent organic framework-sodium alginate-Ca with a diameter of 4–5 mm. 2+ -PAA polymer composite beads (CACPs).

[0067] Performance Characterization

[0068] 1. The TAPB-DMTA prepared in Example 1 was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD):

[0069] Figure 2 AB SEM results show that TAPB-DMTA is a spherical structure with a diameter of 2-3 μm; Figure 3 AFT-IR spectra show that the aldehyde group of DMTP and the amino group of TAPB form an imine bond through condensation; Figure 4 XRD patterns indicate that TAPB-DMTA has a good crystal form. These results demonstrate the successful synthesis of TAPB-DMTA.

[0070] Through SEM ( Figure 2 EF), FT-IR ( Figure 3 B) Thermogravimetric analysis curve (TGA) Figure 5 X-ray photoelectron spectroscopy (XPS) Figure 6 ) and nitrogen adsorption-desorption curve (BET) ( Figure 7 The CACPs prepared in Example 1 were characterized.

[0071] SEM results showed that sodium alginate-Ca 2+ -PAA polymer composite beads (ACPs without added TAPB-DMTA material) Figure 2 Both CD and CACPs exhibit a layered structure with porous cavities. Spherical materials with a diameter of approximately 3 μm exist within the porous structure of CACPs, preliminarily proving the successful incorporation of TAPB-DMTA. The characteristic bands of TAPB-DMTA are not present in ACPs but are present in CACPs in the FTIR spectrum, indicating the successful preparation of the composite beads. TGA curves show that CACPs have good heat resistance (210℃), and the doping of TAPB-DMTA improves the heat resistance of the composite beads. XPS further characterized the elemental composition and chemical bonds of CACPs. The XPS full spectrum of CACPs showed characteristic elemental peaks for C1s, N 1s, O 1s, Na 1s, and Ca 2p. Figure 6 A); C 1s high-resolution spectrum ( Figure 6B) 284.8 eV, 286.4 eV and 288.1 eV correspond to C=C / C-C, C=N / C-N and C=O / C-O characteristic peaks, respectively, confirming the existence of imine bond in TAPB-DMTA; O 1s high resolution spectrum in Figure 6 C) 531.04 and 532.88 eV correspond to O-H and O-C characteristic peaks, respectively, confirming the existence of -OH in TAPB-DMTA, alginate, PAA and C-O-C in TAPB-DMTA and sodium alginate. Figure 7 The nitrogen adsorption-desorption isotherm of CACPs, the BET surface area of CACPs is 122.262 m 2 g -1 , the average pore size Dv(d) is 2.531 nm, which belongs to mesoporous, while the molecular diameter of the five neonicotinoid pesticides is in It shows that CACPs can provide large enough nanochannels for the movement and adsorption of analytes, which proves the existence of pore size effect in the adsorption process.

[0072] Example 2

[0073] A method for detecting neonicotinoid pesticides based on CACPs solid phase extraction, specifically comprising the following steps:

[0074] (1) Extraction and separation pretreatment of standard sample

[0075] Take 10 mL of mixed standard sample of different concentrations of neonicotinoid pesticides (dinotefuran, clothianidin, imidacloprid, acetamiprid, thiamethoxam) (concentrations are 0.05, 0.08, 0.1, 0.5, 1, 5, 10 μg / mL, respectively), add 18 CACPs prepared in Example 1, adjust the solution pH = 6.0 (without adding NaCl), ultrasonic extraction for 40 min (40 kHz, 50 W), and remove the residual solution on the surface of CACPs with a water absorption paper after extraction; place the treated CACPs in a 5 mL centrifuge tube, desorb with 0.5 mL of methanol for 15 min, obtain the eluent, pass through a 0.22 μm nylon membrane, and obtain the standard sample to be tested;

[0076] (2) Construction of standard curve model

[0077] Use the standard sample to be tested obtained in step (1) for HPLC-PDA detection and analysis, take the concentration of neonicotinoid pesticide mixed standard solution as the abscissa and the corresponding peak area as the ordinate to construct a quantitative relationship model;

[0078] The HPLC conditions are as follows: chromatographic column C18 (5 μm, 4.6 x 250 mm); mobile phase is acetonitrile and water (25:75, v:v), flow rate is 1 mL min -1; the detection temperature is 25°C, and the time is 12 min;

[0079] The PDA conditions are: the detection wavelength is 270 nm (dinotefuran, clothianidin, imidacloprid), 246 nm (acetamiprid), and 253 nm (thiamethoxam);

[0080] (3) Determination of the content of neonicotinoid pesticides in the sample to be tested

[0081] 10 mL of the sample solution to be tested is taken, 18 CACPs are added, the solution pH is adjusted to 6.0 (without adding salt), and ultrasonic extraction is performed for 40 min (40 kHz, 50 W). After extraction, the surface residual solution of the CACPs is removed by using a water absorption paper. The treated CACPs are placed in a 5 mL centrifuge tube, desorbed with 0.5 mL of methanol for 15 min, and the sample eluent to be tested is obtained for HPLC-PDA analysis. According to the standard curve model constructed in step (2), the content of neonicotinoid pesticides in the sample to be tested is calculated.

[0082] The standard curve model constructed in step (2) is used to obtain the detection limit (LOD, S / N=3), the quantification limit (LOQ, S / N=10), and the intra-day and inter-day precision, etc. to verify the effectiveness of the method. The specific results are shown in Table 1. The linear range of this method is 0.01-1 μg mL -1 and 1-10 μg mL -1 , R 2 is 0.9963-0.9997, the LOQ is 0.01 μg mL -1 , the LOD is 0.0043-0.0059 μg mL -1 , the inter-day RSD is less than 8.11%, and the batch RSD is less than 7.97%, proving that the method has good repeatability and reproducibility.

[0083] Table 1. Analysis characteristic parameter table of the method

[0084]

[0085] Example 3: Determination of the recovery rate and detection of neonicotinoid pesticides in actual samples

[0086] (1) Recovery rate

[0087] According to the detection method of Example 2, 0.2 mg kg -1 , 0.4 mg kg -1 , and 2 mg kg -1The standard solution of neonicotinoid pesticides was added to the sample matrix of fruits and vegetables at different levels, and the recovery experiment (n = 3) was carried out. As shown in Table 2, the recovery rate of the method for the sample of fruits and vegetables was 73.6% to 116.2%, and the standard deviation was less than 9.9%, which proved that the method had good applicability and feasibility for the detection of trace neonicotinoid pesticides in complex food samples.

[0088] (2) Detection of neonicotinoid pesticides in actual samples

[0089] The peach, pear, lettuce, cucumber and tomato samples were washed with water and cut into small pieces for homogenization. 100 g of the homogenized sample was weighed, and then 8000 r / min -1 centrifugation was performed for 10 min, and the supernatant was collected. The supernatant was filtered through a 0.22 μm water phase filter membrane, the filtrate was diluted 10 times, the pH was adjusted to 6, 18 CACPs were added for ultrasonic-assisted extraction for 40 min, and the surface residual solution of the CACPs was treated with a water absorption paper after extraction. The extracted CACPs were placed in a 5 mL centrifuge tube, desorbed with 0.5 mL of methanol for 15 min, and the eluate was filtered through a 0.22 μm nylon filter membrane. The filtrate was determined by HPLC-PDA according to the method of Example 2. The standard curve was constructed using the blank actual sample as the matrix, and the content of neonicotinoid pesticides in the actual sample was calculated. The results are shown in Table 2:

[0090] In the lettuce and cucumber samples, two neonicotinoid pesticides, dinotefuran and clothianidin, were detected, and in the peach, pear and lettuce samples, the five neonicotinoid pesticides were not detected. The contents of dinotefuran and clothianidin detected in the lettuce sample were 0.105 and <LOQ, respectively, and the contents of dinotefuran and clothianidin detected in the cucumber sample were 0.319 and 0.078 mg / kg -1 , respectively, which were lower than the maximum residue limit specified in GB 2763-2021.

[0091] Table 2. Concentration (mg / kg -1 ), recovery rate (%) and RSD (n = 3) of five neonicotinoid pesticides in actual samples

[0092]

[0093] ND: not detected

[0094] Example 4 Optimization of CACPs synthesis conditions

[0095] In order to synthesize CACPs with stable structure and good extraction effect, the addition amount of Ca 2+ and polyacrylic acid (PAA), the amount of doped TAPB-DMTA, and the size of CACPs were optimized.

[0096] 1、Ca 2+The concentration of Ca2+ has a certain impact on the network structure, stability, and adsorption effect of CACPs, and therefore affects the Ca2+ concentration during the synthesis of CACPs. 2+ The concentration has been optimized.

[0097] The preparation method is the same as in Example 1, except that the Ca in step (2) is adjusted. 2+ The concentrations were 3 mg / mL. -1 6mg mL -1 and 9mg mL -1 Other parameters and conditions are the same as in Example 1.

[0098] Referring to the detection method in Example 2, the composite material prepared above was subjected to a test at 0.2 mg / L. -1 Extraction was performed on standard solutions of five neonicotinoid pesticides, and the results were as follows: Figure 8 As shown, at 6 mg mL -1 The peak areas of the five neonicotinoid pesticides were generally large; the actual graph shows that Ca 2+ Concentration of 3 mg / mL -1 The structure of the CACPs composite beads is relatively loose, and they undergo slight dissociation when dispersed in aqueous solution, which is not conducive to the dispersion and extraction process and reuse; Ca 2+ Concentration of 9 mg / mL -1 CACPs have a relatively compact structure, which is not conducive to the adsorption of target substances.

[0099] 2. The addition of PAA can promote the alginate chain and Ca... 2+ Crosslinking was introduced, along with the introduction of PAA-PAA and PAA-Ca. 2+ The hydrogen bonds and ionic interactions between PAA and alginate improve the stability of the composite beads, thereby enhancing their effectiveness and efficiency in liquid separation. The PAA concentration in the CACPs synthesis process was optimized.

[0100] The preparation method is the same as in Example 1, except that the PAA concentration in step (2) is adjusted to 0.005 mol / L. -1 0.01 mol L -1 0.02 mol L -1 and 0.03 mol L -1 Other parameters and conditions are the same as in Example 1.

[0101] Referring to the detection method in Example 2, the composite material prepared above was subjected to a test at 0.2 mg / L. -1 Extraction was performed on standard solutions of five neonicotinoid pesticides, and the results were as follows: Figure 9 As shown, the results indicate that the PAA concentration is 0.005 mol / L. -1The peak areas of acetamiprid, imidacloprid and thiamethoxam were larger, and the PAA concentration was 0.01 mol / L -1 The peak areas of dinotefuran and thiamethoxam were larger, and the peak areas of the five neonicotinoid pesticides decreased with the increase of PAA concentration, which may be because the polymer diffused into the COF pores during the gel process, occupied the adsorption sites of the COF to the target, thereby reducing the adsorption effect. Considering that the peak areas of dinotefuran and thiamethoxam are much lower, in order to keep the peak areas of the five target objects at a high level, the PAA concentration is selected as 0.01 mol / L -1 .

[0102] 3、TAPB-DMTA as an adsorbent can provide active sites to adsorb neonicotinoid pesticides. Generally, the more the amount of adsorbent, the higher the extraction efficiency. However, due to the incorporation of TAPB-DMTA, the internal network structure of CACPs will change, and the continuous increase of the amount of TAPB-DMTA will increase the difficulty of its uniform dispersion in the sodium alginate solution, and also increase the cost of the analysis method, so the content of TAPB-DMTA needs to be optimized.

[0103] Referring to the preparation method of Example 1, the difference is to adjust the concentration of TAPB-DMTA after adding in step (2) to 5 mg / mL, 10 mg / mL, 25 mg / mL and 50 mg / mL respectively, and other parameters and conditions are the same as Example 1.

[0104] Referring to the detection method of Example 2, the above prepared composite material is used to extract 0.2 mg / L -1 of five kinds of neonicotinoid pesticide standard solution, and the results are shown in Figure 10 The peak areas of the five kinds of neonicotinoid pesticides show an upward trend in the range of 5-50 mg / mL -1 , but the dispersion of COF powder in the sodium alginate solution at a concentration of 50 mg / mL -1 is not good, and the amount of COF added is selected as 25 mg / mL -1 .

[0105] 4、Optimization of the size of CACPs composite beads

[0106] Referring to the preparation method of Example 1, the difference is to adjust the size of the pipette gun head in step (2) to prepare CACPs composite beads of different sizes.

[0107] Referring to the detection method of Example 2, the above prepared composite material is used to extract 0.2 mg / L -1 of five kinds of neonicotinoid pesticide standard solution with the same mass, and the results are shown in Figure 11As shown, when CACPs prepared using a 1mL pipette tip were extracted, the peak areas of the five neonicotinoid pesticides were generally large. Therefore, a 1mL pipette tip was chosen to prepare CACPs.

[0108] Example 5: Optimization of Detection Conditions

[0109] 1. Optimization of pH in the detection system solution

[0110] Referring to the detection method in Example 2, the pH of the solution system was adjusted to 3-9 for 0.2 mg / L. -1 Extraction was performed on standard solutions of five neonicotinoid pesticides, and the results were as follows: Figure 12 As shown, the peak areas of imidacloprid and acetamiprid increased when the solution pH changed from 3 to 6. This may be because the weakly basic pyridine ring in these two analytes is ionized under acidic conditions, which is unfavorable for the adsorption of them by the adsorbent. When the pH changed from 6 to 9, the peak area decreased, possibly because hydrolysis occurred under alkaline conditions. For thiamethoxam and thiamethoxam, the peak area was largest at pH 6 because they are most stable under neutral conditions and degrade under acidic and alkaline conditions; therefore, pH 6 was chosen as the detection condition.

[0111] 2. Selection of salt concentration (NaCl)

[0112] In the dSPE process, ionic strength is one of the main factors affecting extraction efficiency. Adding salt reduces the solubility of the analyte in the sample solution, which is beneficial for extraction; however, adding salt also increases the viscosity of the solution, which is detrimental to extraction. Therefore, the salt ion concentration in the extraction system was optimized.

[0113] Referring to the detection method in Example 2, the salt ion concentration (NaCl) of the solution system was adjusted to 0–10% (w / v) for 0.2 mg / L. -1 Extraction was performed on standard solutions of five neonicotinoid pesticides, and the results were as follows: Figure 13 As shown, within the range of 0–10% (w / v), the extraction efficiency of CACPs for acetamiprid showed a trend of first increasing and then decreasing. Except for acetamiprid, the peak areas of the other four neonicotinoid pesticides all showed a trend of decreasing with increasing salt concentration. In general, the peak areas of the five neonicotinoid pesticides were relatively high when no salt was added, so no salt was added in the subsequent methods.

[0114] 3. Selection of extraction time

[0115] Extraction time is related to the extraction yield. As the extraction time gradually increases, the extraction tends to reach equilibrium, so it needs to be optimized.

[0116] Referring to the detection method in Example 2, the extraction time was adjusted to 5–60 min to investigate the effect on 0.2 mg L... -1The extraction effects of five new neonicotinoid pesticide standard solutions were explored, and the results are shown in Table 1. Figure 14 As shown in Table 1, the peak areas of the five new neonicotinoid pesticides gradually increased first and then tended to be stable after 40 min, indicating that the extraction had reached equilibrium at this time. Therefore, the extraction time was set to 40 min.

[0117] 4. Selection of the number of CACPs

[0118] The number of CACPs directly affects the extraction effect of the analyte. If the number is too small, it may lead to incomplete extraction of the analyte. The effects of different amounts of CACPs on the extraction of new neonicotinoid pesticides were explored.

[0119] Referring to the detection method of Example 2, the number of CACPs in the extraction system was increased from 1 to 18, and the extraction effects of five new neonicotinoid pesticide standard solutions of 0.2 mg L -1 were explored. The results are shown in Table 2. Figure 15 As shown in Table 2, with the number of CACPs increasing from 1 to 10, the peak areas of the five new neonicotinoid pesticides increased rapidly, and slightly increased from 10 to 18. Continuing to increase the number of CACPs is not conducive to subsequent elution operation. Therefore, 18 CACPs were selected as the application in actual detection.

[0120] 5. Selection of elution solvent type

[0121] Referring to the detection method of Example 2, the elution solvents were adjusted to be methanol, acetonitrile, 0.5% ammonia water-methanol, and 0.5% acetic acid-methanol, respectively, and other conditions were unchanged. The five new neonicotinoid pesticide standard solutions of 0.2 mg L -1 were eluted, and the results are shown in Table 3. Figure 16 As shown in Table 3, the elution effects of methanol, acetonitrile, 0.5% ammonia water-methanol, and 0.5% acetic acid-methanol on new neonicotinoid pesticides were investigated. According to the peak area size, acetonitrile showed good elution effect on acetamiprid and imidacloprid, but relatively poor elution effect on dinotefuran, clothianidin, and thiamethoxam; the elution effects of 0.5% ammonia water-methanol and 0.5% acetic acid-methanol on the five new neonicotinoid pesticides were equivalent to those of methanol. Considering comprehensively, methanol was finally selected as the elution solvent.

[0122] 6. Selection of elution solvent volume

[0123] Referring to the detection method of Example 2, the volume of the elution solvent was adjusted to be 0.5-2 mL, and other conditions were unchanged. The five new neonicotinoid pesticide standard solutions of 0.2 mg L -1 were eluted. The results are shown in Table 4. Figure 17As shown, the peak areas of the five triazole pesticides decreased with increasing eluent volume, indicating that neonicotinoid pesticides were completely eluted after 0.5 mL. With increasing eluent volume, the concentration of triazole pesticides in the eluent was gradually diluted, resulting in a decrease in peak area. Furthermore, elutions of 0.5 mL twice and 1 mL twice (with consistent total elution time) were compared. The experimental results show that elution of 0.5 mL once yielded the best results. Therefore, 0.5 mL of eluent was chosen for elution.

[0124] 7. Selection of wash-off time

[0125] Referring to the detection method in Example 2, the elution time was adjusted to 2.5 min to 25 min, while other conditions remained unchanged, for 0.2 mg L... -1 Five neonicotinic pesticide standard solutions were eluted. The results are as follows: Figure 18 As shown, starting from 5 minutes, the peak areas of the five neonicotinoid pesticides gradually increased with the extension of elution time. When the elution time reached 15 minutes, the peak areas no longer showed significant changes, and the elution reached equilibrium. Therefore, the elution time was chosen to be 15 minutes.

[0126] 8. Investigation into Reusability

[0127] The reusability of adsorbent materials is an important performance indicator. The performance of the prepared CACPs was investigated after seven adsorption / desorption cycles. The results are as follows: Figure 19 As shown, the extraction efficiency of the CACPs composite material can be maintained above 90% after 7 adsorption / desorption cycles, indicating that the composite material has good reusability.

[0128] 9. Selective Experiments

[0129] Referring to the detection method of Example 2, the CACPs prepared in Example 1 were used to detect 0.2 mg L... -1 Extraction was performed on neonicotinoid pesticides (dinotefuran, thiamethoxam, thiamethoxam, imidacloprid, acetamiprid), carbamate pesticides (methoprim, fenvalerate, isoprocarb, carbaryl), and benzimidazole pesticide (carbendazim) at various concentrations. The extraction results are as follows: Figure 20 As shown in B, the results indicate that the CACPs prepared in Example 1 have specific selectivity for neonicotinoid pesticides.

[0130] Comparative Example 1

[0131] The preparation method of TAPOB-DMTA composite beads is as follows:

[0132] 1,3,5-Tris(4-aminophenoxy)benzene (TAPOB, 127.82 mg, 0.32 mmol) and 2,5-dimethoxyterephthalaldehyde (DMTA, 93.20 mg, 0.48 mmol) were dissolved in 6 mL of a mixed solution of mesitylene and 1,4-dioxane (v:v = 1:1). The solution was sonicated at room temperature until homogeneous, and then 1 mL of 3 mol·L⁻¹ was added dropwise. -1 The acetic acid aqueous solution was stirred at room temperature for 72 h; then washed three times with methanol, the precipitate was collected by centrifugation, and dried under vacuum at 60 °C overnight to obtain yellow powder TAPOB-DMTA.

[0133] The preparation of TAPOB-DMTA composite beads is the same as step (2) in Example 1.

[0134] Comparative Example 2

[0135] The preparation method of TpPa-SO3H composite beads is as follows:

[0136] 2,4,6-Tricarboxymethylpyrogallol (Tp, 63 mg, 0.3 mmol) and 2,5-diaminobenzenesulfonic acid (Pa-SO3H, 84.7 mg, 0.45 mmol) were dissolved in 3 mL of a mixed solution of trimethylbenzene and 1,4-dioxane (v:v = 4:1). The solution was sonicated at room temperature until homogenized, and then 0.6 mL of 6 mol·L⁻¹ was added dropwise. -1 The mixture was prepared with an aqueous acetic acid solution, transferred to a reaction vessel, and reacted at 120°C for 72 h. The resulting red solid was washed successively with ethanol, water, and ethanol, and then dried under vacuum at 50°C for 12 h to obtain TpPa-SO3H.

[0137] The preparation of TpPa-SO3H composite beads is the same as step (2) in Example 1.

[0138] Comparative Example 3

[0139] The preparation method of TFPB-BD composite beads, the specific steps are as follows:

[0140] 1,3,5-Tris(4-formylphenyl)benzene (TFPB, 62.5 mg, 0.16 mmol) and benzidine (BD, 44.2 mg, 0.24 mmol) were dissolved in 6 mL of a mixed solution of mesitylene and 1,4-dioxane (v:v = 1:1), and the solution was sonicated for 10 min at room temperature. Then, 0.6 mL of 6 mol·L⁻¹ was added dropwise. -1 The acetic acid aqueous solution was allowed to stand at room temperature for 72 h. The resulting yellow product was washed once with THF, DMF and acetone, respectively. The precipitate was collected by centrifugation and dried under vacuum at 60 °C to obtain yellow TFPB-BD powder.

[0141] The TFPB-BD composite beads were prepared according to step (2) of Example 1.

[0142] The composite bead materials prepared in Example 1 and Comparative Examples 1-3 were subjected to extraction of 0.2 mg L-1 of neonicotinoid pesticides (imidacloprid and acetamiprid) according to the method of Reference Example 2, and the results are shown in Table A. -1 Table A Figure 20 Among the four COFs materials, the CACPs formed by TAPB-DMTA prepared in Example 1 had the best extraction effect on neonicotinoid pesticides.

[0143] The examples provided above are not intended to limit the scope of the present application, nor are the described steps intended to limit the order of their execution. Those skilled in the art will make obvious modifications to the present application in combination with existing common knowledge, which also fall within the protection scope defined by the claims of the present application.

Claims

1. A method for detecting neonicotinoid pesticides based on dispersive solid-phase extraction with adsorbents, characterized by, The method comprises: The dispersing solid phase extraction adsorbent is added into the sample solution to be detected to perform the dispersing solid phase extraction, after the extraction is completed, the adsorbent is taken out, the residual solution on the surface of the adsorbent is removed and treated by using the water absorption paper, then the adsorbent is eluted to obtain the eluent, the eluent is filtered to perform the HPLC-PDA detection, and the content of the neonicotinoid pesticide in the sample to be detected is calculated according to the standard curve model; The dispersing solid phase extraction adsorbent is composed of composite beads CACPs. The preparation method of the composite beads CACPs comprises the following steps: (1) synthesis of COF TAPB-DMTA 1,3,5-tris (4-aminophenyl) benzene, 2,5-dimethoxy benzene-1,4-dicarboxaldehyde is dissolved in a mixed solution of mesitylene and 1,4-dioxane, then aqueous acetic acid is added, stirring reaction is carried out at room temperature, after the reaction is completed, the precipitate is separated and collected, washed and dried, and yellow TAPB-DMTA powder is obtained; (2) preparation of CACPs The TAPB-DMTA powder prepared in step (1) is dissolved in a sodium alginate solution to form a TAPB-DMTA-sodium alginate mixed solution, then the mixed solution is added dropwise into a CaCl2-polyacrylic acid receiving solution, magnetic stirring is assisted to make it solidify fully, after shaping, the mixed beads are collected, washed and dried, and the composite beads CACPs are obtained.

2. The method of claim 1, wherein, The concentration of TAPB-DMTA in the TAPB-DMTA-sodium alginate mixed solution of step (2) is 5-50 mg / mL -1 .

3. The method of claim 1, wherein, Ca in the receiving solution in step (2) 2+ concentration of 3-9 mg / mL -1 .

4. The method of claim 1, wherein, The concentration of PAA in the receiving solution in step (2) is 0.005-0.03 mol / L -1 .

5. The method of claim 1, wherein, In step (2), the mixed solution is added dropwise into the CaCl2-polyacrylic acid PAA receiving solution, specifically, a pipette gun is used to control the dropwise amount, and the volume of the gun head of the pipette gun is 20 μL-5 mL.

6. The method of claim 1, wherein, The dispersing solid phase extraction adsorbent is composed of 1-18 composite beads CACPs.

7. The method of claim 1, wherein, The pH value of the sample solution to be detected is 3-9.

8. The method according to any one of claims 1-7 for use in food detection.

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