Preparation of magnetic fluorine functionalized three-dimensional covalent organic framework and application of magnetic fluorine functionalized three-dimensional covalent organic framework in analysis of benzoylurea insecticides

Abstract

The invention belongs to the technical field of adsorbents, and discloses preparation of a magnetic fluorine functionalized three-dimensional covalent organic framework and application of the magnetic fluorine functionalized three-dimensional covalent organic framework in analysis of benzoylurea insecticides, and the preparation method of the magnetic fluorine functionalized three-dimensional covalent organic framework comprises the following steps: mixing an ammonia source, anhydrous sodium acetate, ferric chloride and ethylene glycol according to a ratio, and stirring uniformly; heating, violently stirring and premixing, and then heating and reacting for set time to obtain NH2-Fe3O4; the preparation method comprises the following steps: mixing and grinding tetra (4-aminophenyl) methane, 2, 3, 5, 6-tetrafluoro-p-dibenzaldehyde, NH2-Fe3O4, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-carboxymethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide according to a ratio, introducing nitrogen into a reaction system, emptying air, sealing, and reacting at 20-40 DEG C for 10-30 hours, so as to obtain the tetra (4-aminophenyl) methane, 2, 3, 5, 6-tetrafluoro-p-dibenzaldehyde, NH2-Fe3O4, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-carboxymethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide. And after the reaction is finished, extracting by using an organic solvent, and drying an extracting solution to obtain the NH2-Fe3O4-coated F-3D COF. The NH2-Fe3O4 (at) F-3D COF shows strong adsorption performance on the BUs through the interaction of fluorine-fluorine affinity and hydrogen bonds.

Description

Technical Field

[0001] This invention belongs to the field of adsorbent technology, specifically relating to the preparation of a magnetic fluorine-functionalized three-dimensional covalent organic framework and its application in the analysis of benzoylurea insecticides. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Benzoylurea pesticides (BUs), as growth regulators, differ from traditional neurotoxic pesticides by targeting the chitin synthesis process within insects, thereby disrupting their molting process and inhibiting normal growth and development. Although BUs are widely used to protect crops due to their significant efficacy, they degrade slowly in the environment, and their residues pose a potential threat to human health and ecosystems. Therefore, global regulatory agencies have set stringent maximum residue limits (MRLs) for BUs and require rigorous monitoring of residue levels in agricultural products to ensure food safety.

[0004] Three-dimensional (3D) COFs form a three-dimensional network through covalent bonds, exhibiting unique properties such as high porosity, ample exposure of active sites, and excellent thermal stability. However, conventional solvothermal synthesis methods typically require harsh conditions, such as specific solvents / catalysts, high temperatures of approximately 120°C, sealed environments, and reaction times of up to 3 days. This complex and demanding preparation process severely limits the widespread application of 3D COFs in environments such as magnetic solid-phase extraction (MSPE). Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing a magnetic fluorine-functionalized three-dimensional covalent organic framework and its application in the analysis of benzoylurea insecticides.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a magnetic fluorine-functionalized three-dimensional covalent organic framework, comprising the following steps: Ammonia source, anhydrous sodium acetate, ferric chloride and ethylene glycol were mixed in proportion, heated and stirred vigorously to premix, and then heated to react for a set time to obtain NH2-Fe3O4. Tetra(4-aminophenyl)methane, 2,3,5,6-tetrafluoro-p-dibenzaldehyde, NH2-Fe3O4, 1-butyl-3-methylimidazolium di(trifluoromethanesulfonyl)imide and 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were mixed and ground in a certain proportion. Nitrogen gas was introduced into the reaction system, the air was purged, and the system was sealed. The reaction was then carried out at 20-40℃ for 10-30 h. After the reaction is complete, the mixture is extracted with an organic solvent. The extract is then dried to obtain NH2-Fe3O4@F-3D COF.

[0007] Secondly, the present invention provides a magnetic fluorine-functionalized three-dimensional covalent organic framework, which is prepared by the aforementioned preparation method.

[0008] Thirdly, the present invention provides the application of the magnetic fluorine-functionalized three-dimensional covalent organic framework as an adsorbent, particularly as an adsorbent for benzoylurea insecticides.

[0009] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention successfully designed a mixed ionic liquid-mediated Schiff base polymerization reaction to synthesize magnetic fluorine-functionalized three-dimensional covalent organic frameworks (NH2-Fe3O4@F-3D COFs) from tetra(4-aminophenyl)methane, 2,3,5,6-tetrafluoro-p-dibenzaldehyde (TFPDA), and NH2-Fe3O4 at room temperature. This strategy not only promotes the crystallization of 3D COFs but also enhances their functionality by incorporating carboxyl groups into the framework.

[0010] NH2-Fe3O4@F-3D COF exhibits strong adsorption properties for benzoylurea (BUs) through fluorine-fluorine affinity and hydrogen bonding interactions. Therefore, an MSPE-LC-MS / MS method based on this magnetic composite material was developed for the precise capture and sensitive determination of nine benzoylurea pesticides in apple juice, grape juice, oolong tea, and black tea samples. This method features low limits of detection (0.42–2.93 ng / L) and high precision (RSD < 6.2%). The recoveries of the spiked samples ranged from 74.2% to 119.7%. This study reveals the potential of NH2-Fe3O4@F-3D COF as a highly efficient adsorbent for magnetic solid-phase extraction and its applicability for detecting trace pesticide residues in real food samples. Attached Figure Description

[0011] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0012] Figure 1 This is a flowchart of the synthesis process of NH2-Fe3O4@F-3D COF and its use as a magnetic solid phase extraction material for extracting benzoylurea insecticide; Figure 2Powder X-ray diffraction patterns of F-3D COF under different synthetic conditions: (a) 1,4-dioxane / (3M / 6M / 9M) acetic acid aqueous solution (10 / 1, by volume); (b) reaction in 1,4-dioxane / 6M acetic acid aqueous solution (10 / 1, by volume) for 24 / 48 / 96 h; (c) 1-butyl-3-methylimidazolium di(trifluoromethanesulfonyl)imide / 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (10 / 1, 5 / 1, 5 / 2, by volume); (d) reaction in 1-butyl-3-methylimidazolium di(trifluoromethanesulfonyl)imide / 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (5 / 1, by volume) for 1 / 6 / 12 / 24 h; Figure 3 In the image, (a) infrared spectra of TAM, TFPDA, [Bmim][NTf2], [HOOCmim][NTf2], NH2-Fe3O4, F-3D COFs and NH2-Fe3O4@F-3D COFs; (b) simulated powder X-ray diffraction patterns; (c) powder X-ray diffraction patterns of NH2-Fe3O4, F-3D COFs and NH2-Fe3O4@F-3D COFs; Figure 4 In the image, (a) is a scanning electron microscope (SEM) image of NH2-Fe3O4; (b) is a scanning electron microscope (SEM) image of F-3D COF; (c) is a scanning electron microscope (SEM) image of NH2-Fe3O4@F-3D COF; (d) is a transmission electron microscope (TEM) image of F-3D COF; (e) is a TEM image of NH2-Fe3O4; and (f) is a TEM image of NH2-Fe3O4@F-3D COF. Figure 5 In the image, (a) nitrogen adsorption-desorption isotherms of NH2-Fe3O4, F-3D COF, and NH2-Fe3O4@F-3D COF; (b) pore size distribution of F-3D COF and NH2-Fe3O4@F-3D COF; (c) hysteresis curve of NH2-Fe3O4@F-3D COF; (d) TG curves of F-3D COF and NH2-Fe3O4@F-3D COF; and (e) powder X-ray diffraction pattern of NH2-Fe3O4@F-3D COF after acid and alkali treatment. Figure 6 In the study, the MSPE parameters (n=3) were optimized using a single-factor method: (a) solution pH; (b) adsorbent dosage; (c) adsorption time; (d) eluent type; (e) desorption volume; and (f) desorption time. Detailed Implementation

[0013] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0014] In a first aspect, the present invention provides a method for preparing a magnetic fluorine-functionalized three-dimensional covalent organic framework, comprising the following steps: Ammonia source, anhydrous sodium acetate, ferric chloride and ethylene glycol were mixed in proportion, heated and stirred vigorously to premix, and then heated to react for a set time to obtain NH2-Fe3O4. Tetra(4-aminophenyl)methane, 2,3,5,6-tetrafluoro-p-dibenzaldehyde, NH2-Fe3O4, 1-butyl-3-methylimidazolium di(trifluoromethanesulfonyl)imide and 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were mixed and ground in a certain proportion. Nitrogen gas was introduced into the reaction system, the air was purged, and the system was sealed. The reaction was then carried out at 20-40℃ for 10-30 h. After the reaction is complete, the mixture is extracted with an organic solvent. The extract is then dried to obtain NH2-Fe3O4@F-3D COF.

[0015] The monomers tetra(4-aminophenyl)methane and 2,3,5,6-tetrafluoro-p-dibenzaldehyde were reacted in a mixed solvent of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (5 / 1, by volume) at 30°C for 24 h to obtain highly crystalline yellow F-3D COF. This is because the reaction conditions favor the high reversibility of C=N bonds, thereby enhancing the self-repairing ability of the structure and ultimately yielding high-quality F-3D COF materials. NH2-Fe3O4@F-3D COF prepared by the reaction with NH2-Fe3O4 exhibits strong adsorption performance for BUs through fluorine-fluorine affinity and hydrogen bonding interactions. The preparation process is relatively mild and the preparation efficiency is greatly improved.

[0016] In some embodiments, the ammonia source is hexamethylenediamine, ethylenediamine, or triethylenetetramine.

[0017] In some embodiments, the temperature for heating and vigorous stirring of the premix is ​​45-65°C, and the mixture is stirred until transparent.

[0018] In some embodiments, the temperature of the heating reaction is 180-200°C, and the reaction time is 5-10 hours.

[0019] Preferably, after the reaction is complete, the reaction product is magnetically separated, and the solid product is washed with water and ethanol and then dried to obtain NH2-Fe3O4.

[0020] In some embodiments, the mass ratio of tetra(4-aminophenyl)methane, 2,3,5,6-tetrafluoro-p-dibenzoaldehyde and NH2-Fe3O4 is 20-25:20-30:5-15.

[0021] In some embodiments, the volume ratio of 1-butyl-3-methylimidazolium di(trifluoromethanesulfonyl)imide to 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 30-50:5-10.

[0022] In some embodiments, the mixing and grinding time is 2-5 minutes.

[0023] In some embodiments, the extraction is performed using acetone soxo-extraction for 20-30 hours.

[0024] Preferably, the drying temperature is 70-90℃ and the drying time is 5-10h.

[0025] Secondly, the present invention provides a magnetic fluorine-functionalized three-dimensional covalent organic framework, which is prepared by the aforementioned preparation method.

[0026] Thirdly, the present invention provides the application of the magnetic fluorine-functionalized three-dimensional covalent organic framework as an adsorbent, particularly as an adsorbent for benzoylurea insecticides.

[0027] Fourthly, the present invention provides a method for detecting benzoylurea insecticides, comprising the following steps: The magnetic fluorine-functionalized three-dimensional covalent organic framework was mixed with a sample solution containing benzoylurea insecticides. After sufficient adsorption, magnetic separation was performed to obtain a magnetic solid phase extraction material adsorbed with benzoylurea insecticides. The magnetic solid phase extraction material adsorbed with benzoylurea insecticide was eluted with methanol to obtain an eluent. After evaporating the eluent to dryness, the residue was redissolved with methanol. After the reconstituted solution was filtered, it was detected by LC-MS / MS.

[0028] In some embodiments, the liquid chromatography conditions are: The chromatographic column was a ThermoFisher C18 column, 100 mm × 2.1 mm × 2.6 μm; Mobile phase A is a 4-6 mM ammonium acetate solution, and mobile phase B is acetonitrile; The gradient elution program is as follows: 0-5 min, mobile phase B changes from 90% to 55% by volume; 5-7 min, 55% B.

[0029] Preferably, the column temperature is 25°C and the flow rate is 0.4 mL / min. -1 The injection volume was 5 μL.

[0030] In some embodiments, the benzoylurea insecticides include flufenoxuron, flufenoxuron, flufenoxuron, flufenoxuron, pyridaben, lufenuron, flufenoxuron, flufenoxuron, and flufenoxuron.

[0031] The present invention will be further described below with reference to the embodiments.

[0032] 1.1 Example 1 The synthesis method of 1.2F-3D COF includes the following steps: 1.3 In a centrifuge tube, tetrakis(4-aminophenyl)methane (TAM, 0.06 mmol, 22.8 mg), 2,3,5,6-tetrafluoro-p-dibenzaldehyde (TFPDA, 0.12 mmol, 24.7 mg), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][NTf2], 400 mL), and 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([HOOCmim][NTf2], 80 mL) were added sequentially. After mixing, the mixture was ground for 3 minutes, nitrogen gas was introduced, and the air was expelled before sealing. The centrifuge tube was placed in an oven at 30 °C and reacted for 24 h. After the reaction was completed, ethanol was added for washing, centrifugation was performed, and the solution was extracted with acetone using a Soxhlet extraction method for 24 h. After the Soxhlet extraction was completed, the solution was dried in a drying oven at 80 °C for 8 h to obtain a yellow powder, F-3D COF.

[0033] Example 2 In the preparation of F-3D COF, tetrakis(4-aminophenyl)methane was chosen as the kink and 2,3,5,6-tetrafluoro-p-dibenzaldehyde as the linker to prepare a dia-topologically-based fluorinated three-dimensional covalent organic framework. To obtain materials with optimal performance, the most suitable synthesis conditions were screened by changing experimental conditions such as solvent, catalyst concentration, and reaction time. The screening results are as follows: Figure 2 As shown, the results indicate that highly crystalline yellow F-3D COF can be obtained from the reaction of two monomers in a 5 / 1 (by volume) solvent of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide / 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide at 30 °C for 24 h. This is because the reaction conditions favor the high reversibility of the C=N bond, thereby enhancing the self-repairing ability of the structure and ultimately yielding high-quality F-3D COF material. Subsequently, by adding different masses of NH2-Fe3O4, considering magnetic properties and crystallinity, 10 mg was finally selected as the amount of NH2-Fe3O4@F-3D COF to be prepared.

[0034] The specific synthesis method of NH2-Fe3O4@F-3D COF, such as Figure 1 As shown, it includes the following steps: (1) The synthesis method of NH2-Fe3O4 is as follows: 10 mL of hexamethylenediamine, 4.0 g of anhydrous sodium acetate, 2.0 g of ferric chloride hexahydrate, and 60 mL of ethylene glycol were stirred vigorously at 50 °C until transparent. The mixture was then transferred to a tetrafluoroethylene reactor and reacted at 190 °C for 6 h. After the reaction, magnetic separation was performed, and the mixture was washed three times with water and three times with ethanol, and then dried at 50 °C to obtain NH2-Fe3O4.

[0035] (2) In a centrifuge tube, add tetratetra(4-aminophenyl)methane (TAM, 0.06 mmol, 22.8 mg), 2,3,5,6-tetrafluoro-p-dibenzaldehyde (TFPDA, 0.12 mmol, 24.7 mg), ammonium ferric oxide (NH2-Fe3O4, 10 mg), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][NTf2], 400 mL) and 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([HOOCmim][NTf2], 80 mL); After mixing the above mixture, grind it for 3 minutes, introduce nitrogen gas into it, expel the air, seal it, and react it at a temperature of about 30°C for 24 hours.

[0036] After the reaction is complete, the solid product obtained by magnetic separation is washed several times with water and ethanol until the washing solution is clear.

[0037] After extraction with acetone for 24 hours, the powder was dried in an oven at 80°C for 8 hours to obtain a gray-green powder NH2-Fe3O4@F-3D COF.

[0038] NH 2 -Fe 3 O 4 Structural Analysis of @F-3D COF First, NH2-Fe3O4@F-3D COF was characterized by infrared and powder X-ray diffraction to determine whether imine bonds were formed and whether the composite material was successfully prepared. Figure 3 As shown, NH2-Fe3O4@F-3D COF, as expected, at 1626 cm⁻¹ -1 The characteristic peak at 572 cm⁻¹ is attributed to C=N, indicating the formation of an imine bond. -1 The peak value at this point is related to the Fe-O tensile vibration. A peak value of 1173 cm⁻¹ was detected in NH₂-Fe₃O₄@F-3D COF. -1 (Symmetrical stretching with O=S=O) and 1349 cm -1A peak appears at (asymmetric stretching of O=S=O), indicating the presence of some ionic liquid in NH2-Fe3O4@F-3D COF. The cell parameters of F-3D COF were analyzed by powder X-ray diffraction measurements and structural simulation using Materials Studio software. After performing geometric energy minimization, the cell parameters of F-3D COF were determined to be a = b = 28.7791 Å, c = 9.4526 Å, and α = β = γ = 90°. The simulated powder X-ray diffraction pattern agrees very well with the experimental data. The diffraction peaks observed at 6.15°, 8.70°, and 9.87° correspond to space group I4, respectively. 1 / a

[200] ,

[220] , and

[101] crystal planes of (No. 88). Powder X-ray diffraction comparisons of F-3D COF, NH2-Fe3O4, and NH2-Fe3O4@F-3D COF showed good consistency, confirming the successful preparation of the composite material and that it did not affect the structural integrity or crystallinity of NH2-Fe3O4 and F-3D COF.

[0039] High-magnification scanning electron microscope (SEM) images and transmission electron microscope (TEM) images of NH2-Fe3O4, F-3D COF, and NH2-Fe3O4@F-3D COF are shown below. Figure 4 As shown in the figure, the NH2-Fe3O4@F-3D COF material has a rod-like structure, consisting of a large number of rods with a diameter >2 micrometers, on which NH2-Fe3O4 spheres with an average diameter of 50nm are attached.

[0040] As a porous material, the pore size and specific surface area properties are crucial, especially for adsorption applications. Therefore, the nitrogen adsorption / desorption, pore size distribution, and specific surface area of ​​F-3D COF and NH2-Fe3O4@F-3D COF were characterized. Figure 5 The adsorption-desorption curves of F-3D COF and NH2-Fe3O4@F-3D COF show that both isotherms belong to typical Type IV isotherms, implying that the synthesized materials possess mesoporous properties. Furthermore, the specific surface areas of F-3D COF and NH2-Fe3O4@F-3D COF are 379.8 m² and 379.8 m², respectively. 2 / g and 333.5 m 2 / g, with average pore sizes of 2.77 nm and 2.79 nm, and pore volumes of 0.263 cm³, respectively. 3 / g and 0.233 cm 3 / g.

[0041] hysteresis loop, such as Figure 5As shown in d, neither exhibits significant hysteresis, and their VSM curves show similar shapes and symmetry. The saturation magnetization (Ms) of NH2-Fe3O4 is 78.2 emu / g, while that of NH2-Fe3O4@F-3D COF is 12.9 emu / g. While the value is slightly lower, it still possesses high magnetic susceptibility, achieving rapid magnetic separation within a short time.

[0042] Stability analysis of NH2-Fe3O4@F-3D COF The thermal and chemical stability of NH2-Fe3O4@F-3D COF was investigated. Figure 5 d indicates that mass loss only begins in NH2-Fe3O4@F-3D COF when the temperature reaches 320℃, which may be due to the collapse and decomposition of the NH2-Fe3O4@F-3D COF framework. In addition, the chemical stability of this material was investigated by dispersing it in HCl (10 mM) and NaOH (10 mM) for 2 days. Figure 5 e). Surprisingly, even under harsh acid and alkaline solutions, the positions of the PXRD peaks were consistent with the initial results for the material, indicating that the chemical and skeletal structure of the material remained unchanged. These results demonstrate the potential of robust NH₂-Fe₃O₄@F-3D COF as an adsorbent material capable of adsorbing benzoylurea pesticides from complex food samples.

[0043] Optimization of extraction and analysis conditions for magnetic solid-phase extraction using single-factor method Six experimental parameters were optimized using single-factor methods, including sample pH, adsorbent dosage, extraction time, desorption solvent, desorption liquid volume, and desorption time. Ultrapure water containing nine benzoylurea insecticides at a concentration of 10 μg / L was used as samples, and recovery experiments were conducted under different conditions to evaluate the efficiency of the MSPE and obtain the optimal experimental parameters.

[0044] The effect of sample pH on MSPE performance was evaluated within a pH range of 2-10. Figure 6 As shown in Figure a, the recoveries of the nine benzoylurea insecticides initially increased with increasing pH, reaching a maximum under neutral conditions (pH=7), and then decreased at more extreme pH values. This trend may be attributed to the instability of benzoylurea insecticides, which readily dissociate or hydrolyze under strongly acidic or alkaline conditions. Under acidic conditions, high concentrations of H⁺ ions may interfere with the interaction between the adsorbent and the target molecules, thereby weakening their binding affinity. Furthermore, since the pKa values ​​of all nine benzoylurea insecticides are above 8.1, the compounds exist primarily in anionic form at pH>8, which may also reduce adsorption efficiency. Therefore, pH=7 was chosen as the optimal pH for adsorption.

[0045] The amount of adsorbent directly affects adsorption capacity and extraction efficiency. Insufficient adsorbent leads to a reduction in adsorption sites and incomplete capture of the target compound, while excessive adsorbent increases cost without significantly improving recovery. Adsorbent dosages of 3-12 mg were evaluated. Figure 6 (b) The recovery rate increased with increasing adsorbent dosage. When the adsorbent dosage was 9 mg, the recovery rates of all nine benzoylurea insecticides exceeded 80%. Further increasing the dosage had little effect on the recovery rate. Therefore, 9 mg was chosen for subsequent experiments.

[0046] The effect of extraction time (5-20 minutes) on the recovery rate of benzoylurea insecticides was studied. Figure 6 c). When the extraction time was between 5 and 15 minutes, the recovery rate of some benzoylurea insecticides was less than 70%. When the extraction time was further extended to 20 minutes, the recovery rate of all nine benzoylurea insecticides exceeded 80%, indicating that adsorption equilibrium was achieved within this time range. To balance efficiency and time, 20 minutes was selected as the optimal extraction time in subsequent experiments.

[0047] The polarity and solubility of the desorption solvent affect the release of the target compound from the adsorbent. The desorption performance of four commonly used solvents (n-hexane, dichloromethane, acetonitrile, and methanol) was evaluated. Figure 6 d). Only methanol yielded satisfactory recoveries for all nine benzoylurea insecticides. Therefore, methanol was chosen as the optimal desorption solvent.

[0048] This study investigated the effects of solvent adsorption volume (2-10 mL) and desorption time (5-20 min) on the properties of MSPE. Figure 6 (e and 6f). A satisfactory recovery was achieved with an 8 mL desorption solvent volume, but further increases in solvent volume did not significantly improve the recovery. Therefore, 8 mL was chosen as the optimal desorption volume. Similarly, the recovery reached equilibrium within 10 minutes, with recoveries exceeding 80% for all nine benzoylurea insecticides. Extending the desorption time beyond 10 minutes did not significantly improve the recovery. Therefore, a 10-minute desorption time was used in subsequent experiments.

[0049] 1.4 The final magnetic solid-phase extraction process: Weigh 9 mg of NH2-Fe3O4@F-3D COF sample and transfer it to a glass sample vial. Then add 20 mL of sample solution containing a standard solution of benzoylurea insecticides. Rotate the mixture in a rotary mixer (80 rpm / min) for 20 min at room temperature, then perform magnetic separation using a magnet. Desorb the benzoylurea insecticides from the material by shaking with 8 mL of chromatographic grade methanol for 10 min. Evaporate the eluent to dryness under a nitrogen stream at 30°C. Redissolve the residue in 0.5 mL of methanol, filter through a 0.22 μm organic phase membrane, and inject into an LC-MS / MS system for analysis of benzoylurea insecticides.

[0050] Liquid Chromatography-Tandem Mass Spectrometry Conditions HPLC-MS / MS Instrument: Ultimate 3000 liquid chromatograph tandem with QTRAP 5500 mass spectrometer. HPLC Conditions: Thermo Fisher C18 column (100 mm × 2.1 mm × 2.6 μm); column temperature: 25℃; mobile phase: 5 mM ammonium acetate in water (A) and acetonitrile (B); gradient elution: 0–5.0 min, 55%–90% B; 5.0–7.0 min, 55% B; flow rate: 0.4 mL / min -1 Injection volume: 5 μL.

[0051] Mass spectrometry conditions: Ion source: electrospray ionization (ESI) in negative ion mode; Scan mode: multiple reaction monitoring (MRM); Ion source temperature: 500 °C; Other parameters are shown in Table 1.

[0052] Table 1. Mass spectrometry parameters of nine benzoylurea insecticides

[0053] The established analytical method was evaluated by examining the linear range, correlation coefficient, limit of detection (LOD), limit of quantitation (LOQ), precision, and other relevant parameters. The corresponding quantitative results are shown in Table 2. The linear range for the eight benzoylurea insecticides using this method was 12.5–10000.0 ng / L, and for fluazinam, it was 25.0–10000.0 ng / L, with a correlation coefficient R > 0.9960. The LOD was calculated based on a signal-to-noise ratio (S / N) of 3, and the results were 0.42–2.93 ng / L, significantly lower than methods reported in other literature. The LOQ was calculated based on S / N = 10, ranging from 1.40–9.77 ng / L. For the nine benzoylurea insecticides, the intra-day bias (n = 5) and inter-day bias (n = 5) were 3.4%–5.4% and 3.8%–6.2%, respectively. These data demonstrate the high sensitivity and reliability of the established analytical method, which shows great promise for the extraction and analysis of trace or ultra-trace levels of benzoylurea pesticides in complex real-world samples.

[0054] Table 2 Analytical parameters of magnetic solid phase extraction

[0055] Detection of benzoylurea pesticides in actual fruit juice and tea beverage samples by magnetic solid phase extraction combined with LC-MS / MS After successfully constructing a quantitative method for detecting benzoylurea insecticides based on the newly prepared NH2-Fe3O4@F-3D COF, this method was applied to determine benzoylurea insecticides in food samples (e.g., apple juice, grape juice, oolong tea, and black tea) to verify its practicality.

[0056] 1.5 Food Sample Collection and Pretreatment Two fruit juices (apple and grape juice) and two tea beverages (oolong and black tea) were purchased from a local supermarket in Jinan, China. After opening, the samples were stored at 4°C and used within one week. Each sample was filtered, and 10 mL of the filtrate was diluted with 10 mL of ultrapure water. The pH of the diluted solution was adjusted to approximately 7 for subsequent magnetic solid-phase extraction.

[0057] As shown in Table 3, trace levels of fluorouracil were detected in the selected real samples, ranging from 19.9 to 34.2 ng / L, in apple juice, grape juice, and oolong tea beverages. Spiking recovery experiments were then conducted by adding three different concentration levels (50, 2500, and 5000 ng / L) to the apple juice, grape juice, oolong tea, and black tea samples.

[0058] The experimental results showed that the recoveries of the spiked pesticides in the two fruit juice samples ranged from 74.2% to 119.7%, with relative standard deviations (RSDs) ranging from 0.5% to 8.7%. Similarly, the recoveries of the spiked pesticides in the two tea beverages ranged from 78.5% to 118.0%, with RSDs ranging from 0.7% to 8.4%. These results demonstrate that this method can rapidly, accurately, and sensitively analyze trace amounts of benzoylurea pesticides in real food samples.

[0059] Table 3 Analytical results of the actual samples to be tested

[0060] a spiked level: 50 ng / L -1 . b spiked level: 2500 ng / L -1 . c Spiked level: 5000ng / L -1 . d Not detected. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic fluorine-functionalized three-dimensional covalent organic framework, characterized in that: Includes the following steps: Ammonia source, anhydrous sodium acetate, ferric chloride and ethylene glycol were mixed in proportion, heated and stirred vigorously to premix, and then heated to react for a set time to obtain NH2-Fe3O4. Tetra(4-aminophenyl)methane, 2,3,5,6-tetrafluoro-p-dibenzaldehyde, NH2-Fe3O4, 1-butyl-3-methylimidazolium di(trifluoromethanesulfonyl)imide and 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were mixed and ground in a certain proportion. Nitrogen gas was introduced into the reaction system, the air was purged, and the system was sealed. The reaction was then carried out at 20-40℃ for 10-30 h. After the reaction is complete, the mixture is extracted with an organic solvent. The extract is then dried to obtain NH2-Fe3O4@F-3D COF.

2. The method for preparing the magnetic fluorine-functionalized three-dimensional covalent organic framework according to claim 1, characterized in that: The ammonia source is hexamethylenediamine, ethylenediamine, or triethylenetetramine; Preferably, the temperature for heating and vigorous stirring during premixing is 45-65℃, and stirring is continued until the mixture becomes transparent; Preferably, the heating reaction temperature is 180-200℃, and the reaction time is 5-10 hours; Preferably, after the reaction is complete, the reaction product is magnetically separated, and the solid product is washed with water and ethanol and then dried to obtain NH2-Fe3O4.

3. The method for preparing the magnetic fluorine-functionalized three-dimensional covalent organic framework according to claim 1, characterized in that: The mass ratio of tetra(4-aminophenyl)methane, 2,3,5,6-tetrafluoro-p-dibenzaldehyde, and NH2-Fe3O4 is 20-25:20-30:5-15.

4. The method for preparing the magnetic fluorine-functionalized three-dimensional covalent organic framework according to claim 1, characterized in that: The volume ratio of 1-butyl-3-methylimidazolium di(trifluoromethanesulfonyl)imide to 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 30-50:5-10.

5. The method for preparing the magnetic fluorine-functionalized three-dimensional covalent organic framework according to claim 1, characterized in that: The mixing and grinding time is 2-5 minutes; Preferably, the extraction is performed using acetone soxhlet extraction for 20-30 hours; Preferably, the drying temperature is 70-90℃ and the drying time is 5-10h.

6. A magnetic fluorine-functionalized three-dimensional covalent organic framework, characterized in that: It is prepared by any one of the preparation methods described in claims 1-5.

7. The application of the magnetic fluorine-functionalized three-dimensional covalent organic framework of claim 6 as an adsorbent, particularly as an adsorbent for benzoylurea insecticides.

8. A method for detecting benzoylurea insecticides, characterized in that: Includes the following steps: The magnetic fluorine-functionalized three-dimensional covalent organic framework of claim 6 is mixed with the test sample solution containing benzoylurea insecticide. After sufficient adsorption, magnetic separation is performed to obtain a magnetic solid phase extraction material adsorbed with benzoylurea insecticide. The magnetic solid phase extraction material adsorbed with benzoylurea insecticide was eluted with methanol to obtain an eluent. After evaporating the eluent to dryness, the residue was redissolved with methanol. After the reconstituted solution was filtered, it was detected by LC-MS / MS.

9. The method for detecting benzoylurea insecticides according to claim 8, characterized in that: Liquid chromatography conditions: The chromatographic column was a ThermoFisher C18 column, 100 mm × 2.1 mm × 2.6 μm; Mobile phase A is a 4-6 mM ammonium acetate solution, and mobile phase B is acetonitrile; The gradient elution program is as follows: 0-5 min, mobile phase B changes from 90% to 55% by volume; 5-7 min, 55% B. Preferably, the column temperature is 25°C and the flow rate is 0.4 mL / min. -1 The injection volume was 5 μL.

10. The method for detecting benzoylurea insecticides according to claim 9, characterized in that: The benzoylurea insecticides include flufenoxuron, flufenoxuron, flufenoxuron, flufenoxuron, pyridaben, lufenuron, flufenoxuron, flufenoxuron, and flufenoxuron.

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