Covalent organic framework materials and solid-phase microextraction fibers synthesized based on ionic liquid catalysis and their application in aflatoxin contamination early warning.

Abstract

This invention belongs to the field of solid-phase microextraction fiber technology, specifically relating to covalent organic framework materials synthesized based on ionic liquid catalysis and solid-phase microextraction fibers, and their application in aflatoxin contamination early warning. This invention uses ionic liquids as solvents and catalysts in the synthesis reaction of covalent organic framework materials, rapidly synthesizing ionic liquid-containing COFs (IL-COFs) in an open system at room temperature and atmospheric pressure. The solid-phase microextraction fiber is obtained by coating stainless steel wire with IL-COFs and then curing it. Using this solid-phase microextraction fiber for the extraction of aflatoxin and its precursors achieves highly selective and efficient adsorption. Combining IL-COF-based solid-phase microextraction with ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS / MS) enables simultaneous, sensitive, and accurate determination of aflatoxin and its precursors in samples. Furthermore, this detection method can be used to obtain the dynamic relationship between aflatoxin and its precursors, thereby providing early warning of aflatoxin contamination.

Description

Technical Field

[0001] This invention belongs to the field of solid-phase microextraction fiber technology, specifically relating to a covalent organic framework material and solid-phase microextraction fiber based on ionic liquid catalysis synthesis, and their application in aflatoxin pollution early warning. Background Technology

[0002] Solid-phase microextraction (SPME), as a powerful microextraction technique, has attracted much attention due to its outstanding advantages such as small sample volume, simple workflow, low solvent consumption, and environmental friendliness, and has been widely used in food, medicine, biology, environment, and other fields. The key to SPME technology lies in the fiber coating; the performance of the coating directly affects the extraction efficiency of the target analyte and the sensitivity of the detection method. Therefore, developing novel coating materials with high extraction performance and high selectivity is of great significance for expanding the application of SPME technology.

[0003] Covalent organic frameworks (COFs) are highly porous crystalline materials formed by covalent bonds between light elements such as C, N, O, and B. They possess characteristics such as high specific surface area, good stability, periodic porosity, and ease of functionalization. Furthermore, the inherent π-electron system and hydrophobic framework of COFs endow them with a strong affinity for most aromatic pollutants, making them widely used as extraction media in sample pretreatment and a promising SPME coating material. However, current synthesis methods for COFs are mainly solvothermal methods, which typically require long reaction times, harsh reaction conditions, cumbersome synthesis steps, and indispensable catalysts, limiting the further application of COFs. In the synthesis of COFs, acetic acid, a typical catalyst, has low catalytic efficiency. Although new catalysts such as metal trifluoromethanesulfonates have been developed (Matsumoto M, Dasari RR, Ji W, et al. Rapid, low temperature formation of imine-linked covalentorganic frameworks catalyzed by metal triflates [J]. Journal of the American Chemical Society, 2017, 139: 4999-5002), p-Toluenesulfonic acid (Karak S, Kandambeth S, Biswal BP, et al. Constructing ultraporous covalent organic frameworks in seconds via an organic terracotta process [J]. Journal of the American Chemical Society, 2017, 139: 1856-1862) has been reported to accelerate the formation of COFs. However, these catalysts may contaminate porous materials with inorganic residues or byproducts, and also increase synthesis costs and operational complexity. Ma et al. reported a solvent-free and catalyst-free method for synthesizing azazine-linked COFs using irreversible enol-keto tautomerization (Li X, Wu Q, Li S, et al. Solvent- and catalyst-free synthesis of anazine-linked covalent organic framework and the induced tautomerization in the adsorption of U(VI) and Hg(II) [J]. Green Chemistry, 2019, 21: 649-657). However, the universality of this method and the porosity of the product still need further improvement. Therefore, developing a simple, efficient, and environmentally friendly method to synthesize high-porosity crystalline COFs has always been a research hotspot in this field.

[0004] Currently, aflatoxins (AFs) and their precursors often co-contaminate cereals and their processed products. Given the trace levels of AFs and their precursors and the complexity of cereal food matrices, sample pretreatment is a crucial step before AFs and their precursor analysis. Furthermore, precursors in the AFs biosynthetic pathway can serve as early warning indicators of AFs contamination. Monitoring changes in precursor content to identify and predict potential AFs contamination risks allows for timely preventative and control measures, representing an effective strategy for ensuring cereal safety. Since AFs and their precursors are organic compounds composed of benzene rings and oxocyclic rings, containing ester, carbonyl, and methoxy groups, and carbonyl groups (COFs) can serve as excellent extraction media for AFs and their precursors, developing a simple and efficient method for synthesizing high-porosity crystalline COFs, applying SPME technology based on these COFs to sample pretreatment of aflatoxins and their precursors in cereal samples, establishing simultaneous and accurate detection methods for AFs and their precursors, and developing precursor-based AFs contamination early warning methods are of great significance. Summary of the Invention

[0005] To address the problems of long reaction times, high temperatures, cumbersome steps, harsh reaction conditions, and low catalytic efficiency of existing catalysts in the synthesis of COFs, this invention provides a simple, efficient, green, and environmentally friendly method for synthesizing high-porosity crystalline COFs. This method uses imidazole ionic liquids (ILs) as solvents and catalysts for the COF synthesis reaction, and rapidly synthesizes IL-containing COFs (IL-COFs) in an open system at room temperature and atmospheric pressure. The building blocks of these IL-COFs are linked by imine bonds, resulting in a stable structure. The small amount of encapsulated ILs provides more adsorption sites and multiple functions, promoting efficient extraction of AFs and their precursors. Furthermore, this invention provides SPME fibers based on IL-COFs for efficient extraction of four AFs (B1, B2, G1, and G2) and their three precursors (AVN, OMST, and ST). Combined with ultra-high performance liquid chromatography-liquid chromatography / mass spectrometry (UHPLC-MS / MS), it provides a sensitive and accurate detection method for simultaneously determining seven target analytes in a sample. In addition, this invention uses AF precursors as early warning indicators to establish an AFs early warning method based on this detection method.

[0006] The present invention specifically adopts the following technical solution:

[0007] This invention provides a covalent organic framework material synthesized based on ionic liquid catalysis, the preparation method of which includes:

[0008] An aqueous acetic acid solution is added to a mixture of an amino monomer, an aldehyde monomer, and an imidazole ionic liquid. After mixing, the mixture is allowed to react statically at room temperature, atmospheric pressure, and an open environment to obtain covalent organic framework materials (IL-COFs). The imidazole ionic liquid serves as both a solvent and a catalyst. The reaction time is at least 1 hour, preferably 1 hour to 24 hours.

[0009] In a further embodiment, the amino monomer is 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) or 1,3,5-tris(4-aminophenyl)benzene (TAPB).

[0010] The aldehyde monomer is 2,5-dibromophenyl-1,4-dicarboxaldehyde (BrTA), 2,5-dihydroxy-1,4-benzenedicarboxaldehyde (OHTA), or 2,5-dimethoxyphenyl-1,4-dicarboxaldehyde (OMeTA).

[0011] The imidazole-based ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][Tf2N]), 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIM][Tf2N]), or 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4).

[0012] In a further embodiment, the molar ratio of the amino monomer, aldehyde monomer, and acetic acid is 1:1.5:21.3, and the molar ratio of the amino monomer to the imidazole ionic liquid is 56.4 μmol:1 mL.

[0013] In a further embodiment, after the reaction is allowed to stand, the product is washed and dried to obtain IL-COFs. The washing involves washing the product sequentially with tetrahydrofuran and anhydrous ethanol, and the drying involves drying the product in a vacuum oven at 60 °C for 10-14 h.

[0014] Furthermore, this invention utilizes the adsorption efficiency results of different IL-COFs for four AFs (B1, B2, G1, and G2) and their three precursors OMST, AVN, and ST to determine the optimal monomers for composing COFs and the optimal ILs for catalytic synthesis of IL-COFs. The results show that, as a preferred embodiment, the amino monomer is 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, the aldehyde monomer is 2,5-dibromophenyl-1,4-dicarboxaldehyde, and the imidazole ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, denoted as IL. ([BMIM][Tf2N]) -COF (TAPT-BrTA) .

[0015] This invention also provides a solid-phase microextraction fiber, which refers to a stainless steel wire coated with an IL-COFs coating. As one embodiment, the stainless steel wire has a diameter of 500 μm and a length of 9 cm; the coating is IL-COFs. ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coating is 480 μm thick. A small amount of coating on the steel wire can achieve efficient extraction. For example, the coating length is 1.8 cm. When using it, the coated steel wire is immersed in the extraction liquid for extraction.

[0016] The method for preparing the solid-phase microextraction fiber includes: coating the covalent organic framework material onto the surface of a stainless steel wire using an adhesive, followed by heating and curing. Specifically, as follows:

[0017] After cleaning, the stainless steel wire is coated with adhesive and immediately immersed in IL-COF powder to form an IL-COF coating on the surface of the stainless steel wire. This process is then cured. Repeating this operation increases the coating thickness. Finally, adhesive is applied again and cured. The curing is carried out at 80°C. The adhesive can be polyacrylonitrile (PAN) glue.

[0018] This invention also provides the application of the above-mentioned solid-phase microextraction fiber in the detection of aflatoxin and / or aflatoxin precursors.

[0019] This application targets aflatoxin and / or aflatoxin precursors, and uses IL-COF-based solid-phase microextraction technology coupled with UHPLC-MS / MS to establish a sensitive and accurate IL-COF-SPME-UHPLC-MS / MS detection method for determining the target analytes in samples. The method includes the following steps:

[0020] Aflatoxin and / or aflatoxin precursors were extracted from the sample to obtain a sample extract. The sample extract was then subjected to solid-phase microextraction using the fiber described above, followed by analysis using ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS / MS) to obtain quantitative results for aflatoxin and / or aflatoxin precursors. The aflatoxins were aflatoxins B1, B2, G1, and / or G2 (AF(B1, B2, G1, and G2)), and the aflatoxin precursors were averlantin, aflatoxin var. chromophore, and / or O-methylaflatoxin var. chromophore (OMST, AVN, and / or ST).

[0021] The specific steps for extracting aflatoxin and / or its precursors from the sample are as follows:

[0022] The sample was pulverized, and a weight was taken. An acetonitrile / water (80:20, v / v) solution was added, vortexed, and then extracted by sonication. After centrifugation, the supernatant was collected, concentrated to near dryness by nitrogen blowing, and the residue was reconstituted with water. The volume ratio of the pulverized sample to the acetonitrile / water (80:20, v / v) solution was 1 g: 4 mL.

[0023] In a further embodiment, the desorbent in the solid-phase microextraction process is methanol, ethanol, acetonitrile, ethyl acetate, or acetone.

[0024] The extraction time in the solid-phase microextraction process is 20–60 min.

[0025] The desorption time during the solid-phase microextraction process is 5–25 min.

[0026] In the optimized solid-phase microextraction method, the extraction time is 50 min. Acetone is used as the desorbent, and the desorption time is 5 min.

[0027] This invention also provides the application of the solid-phase microextraction fiber in the early warning of Aspergillus flavus contamination, including:

[0028] The precursors aflatoxin, averlantin, aflatoxin monoxide, and O-methylaflatoxin monoxide were used as early warning indicators of aflatoxin contamination. The established IL-COF-SPME-UHPLC-MS / MS method was used to quantitatively detect the aflatoxin precursors in the samples, so as to provide early warning of aflatoxin contamination in the samples.

[0029] This invention provides a method for early warning of aflatoxin contamination, comprising: quantitative detection of aflatoxin precursors in a sample to provide early warning of aflatoxin contamination in the sample; the quantitative detection includes: extracting aflatoxin precursors from the sample to obtain a sample extract, performing solid-phase microextraction on the aflatoxin precursors in the sample using the aforementioned solid-phase microextraction fiber, and then analyzing the extract using ultra-high performance liquid chromatography-mass spectrometry to obtain quantitative results of the aflatoxin precursors.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) Existing COFs synthesis methods require long reaction time, harsh reaction conditions, complicated synthesis steps and inefficient catalysts. However, this invention uses ILs as the solvent and catalyst for the reaction and develops a simple, efficient, green and environmentally friendly method that can quickly synthesize high porosity crystalline COFs at room temperature and atmospheric pressure in an open environment.

[0032] (2) The IL synthesized in this invention ([BMIM][Tf2N]) -COF (TAPT-BrTA) It possesses a large specific surface area and a hierarchical porous structure, while containing a large number of π electron systems and abundant bromine atoms that can serve as electron-withdrawing groups. The small amount of encapsulated ILs can also provide more adsorption sites, enabling it to generate multiple interactions with the target analytes. It can also efficiently extract four AFs (B1, B2, G1, G2) and their three precursors OMST, AVN, and ST.

[0033] (3) The IL-COFs (such as IL-COFs) prepared in this invention ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coated fiber has excellent durability and reusability, and can be reused at least 30 times. It can withstand multiple adsorption-desorption operations without damage, and has great application potential in the extraction of trace target substances in real samples.

[0034] (3) This invention establishes for the first time a detection method for simultaneously determining four AFs (B1, B2, G1, G2) and their three precursors OMST, AVN and ST, and applies it to the sensitive and accurate determination of AFs and their precursors in actual grain samples as well as the early warning of AF contamination, providing an effective early warning method for AF contamination in grain samples. Attached Figure Description

[0035] Figure 1 : Schematic diagram of the synthesis of IL-COFs.

[0036] Figure 2 Characterization of IL-COFs. (a) FT-IR plots of 6 IL-COFs; (b) IL-COFs. ([BMIM][Tf2N]) -COF (TAPB-OMeTA) IL([BMIM][Tf2N]) -COF (TAPT-OMeTA) IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) IL ([HMIM][Tf2N]) -COF (TAPT-BrTA) PXRD plot; (c) IL ([BMIM][BF4]) -COF (TAPT-BrTA) PXRD plot; (d) IL ([BMIM][Tf2N]) -COF (TAPT-OHTA) PXRD plot.

[0037] Figure 3 Effects of monomer type and IL type on adsorption efficiency. (a) Monomer type; (b) IL type.

[0038] Figure 4 :IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Characterization. (a) N2 adsorption / desorption analysis; (b) pore size distribution map; (c) scanning electron microscope image; (d) surface scans of C, N, Br and F elements; (e) high-resolution transmission electron microscope image; (f) 13 C solid-state nuclear magnetic resonance spectrum.

[0039] Figure 5 IL synthesized at different reaction times ([BMIM][Tf2N]) -COF (TAPT-BrTA) PXRD plot.

[0040] Figure 6 :IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Scanning electron microscope images of the coated fibers. (a) SPME fiber, (b) magnified view of a region of the SPME fiber.

[0041] Figure 7 SPME condition optimization. (a) Extraction time, (b) Desorbent type, (c) Effect of desorption time on extraction efficiency.

[0042] Figure 8 :IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The memory effect of coated fibers.

[0043] Figure 9 :IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) A comparison between coated fibers and commercial fibers.

[0044] Figure 10 :IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Reusability of coated fibers.

[0045] Figure 11Chromatogram of a spiked peanut sample after SPME treatment.

[0046] Figure 12 Photographs of peanuts infected with A. flavus stored for 7 days.

[0047] Figure 13 : Dynamic changes of AFs and precursors in stored peanuts. (a) AF precursors, (b) AFs.

[0048] Figure 14 Correlation analysis heatmap of AFs and precursors in stored peanuts. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0050] This invention first prepares and screens covalent organic framework materials with optimal adsorption performance based on different amino monomers, aldehyde monomers, and ionic liquids. Then, solid-phase microextraction fibers based on these covalent organic framework materials are prepared, and the parameters for extracting four AFs (B1, B2, G1, G2) and their three precursors OMST, AVN, and ST are optimized. Finally, the optimized extraction technology is combined with UHPLC-MS / MS and applied to the determination of four AFs (B1, B2, G1, G2) and their three precursors OMST, AVN, and ST in peanut samples from different varieties, establishing an early warning method for AF pollution.

[0051] The different varieties of peanuts used in the embodiments of this invention were purchased from the Henan Academy of Agricultural Sciences.

[0052] In this example, the UHPLC-MS / MS analytical conditions were as follows: An Agilent 1290 liquid chromatography system equipped with an electrospray ionization source was coupled with a 6470 triple quadrupole mass spectrometer for analysis. Chromatographic separation was performed using an Agilent C18 column (2.1 mm × 50 mm, 1.8 μm), with a mobile phase consisting of A (0.1% formic acid in water) and B (acetonitrile). The gradient elution program was: 0–1.5 min, 40% B; 1.5–4 min, 40–95% B; 4–6 min, 95% B; 6–6.5 min, 95–40% B; 6.5–8 min, 40% B. The flow rate was 0.2 mL / min, the injection volume was 5 μL, and the column temperature was 40 °C. Analytes were detected in positive ion mode using multiple reaction monitoring (MRM) MS / MS acquisition mode. The main ion source parameters are as follows: drying gas temperature 300 ℃, drying gas flow rate 5 L / min, sheath gas temperature 350 ℃, sheath gas flow rate 11 L / min, nebulizer pressure 45 psi, capillary voltage 3500 V, and nozzle voltage 500 V. High-purity nitrogen is used as the drying gas, sheath gas, and nebulizing gas.

[0053] Example 1: Synthesis of Covalent Organic Framework Materials Catalyzed by Ionic Liquids

[0054] 1. Preparation of covalent organic framework materials by ionic liquid catalysis

[0055] Six IL-COFs were synthesized by selecting two amino monomers (TAPB and TAPT), three aldehyde monomers (OMeTA, BrTA, and OHTA), and three ILs containing different anions / cations ([BMIM][Tf2N], [HMIM][Tf2N], and [BMIM][BF4]). The synthesis schematic diagram is shown below. Figure 1 As shown. ILs serve as both solvent and catalyst. The specific operating steps are as follows:

[0056] The amino monomer (56.4 μmol), aldehyde monomer (84.6 μmol), and 1 mL of ILs were mixed and magnetically stirred for 10 min. Then, 0.2 mL of acetic acid aqueous solution (6 mol / L) was added, and stirring was continued for 1 min to form a homogeneous dispersion. The mixture was allowed to stand at room temperature for 12 h. The solid product was collected, washed three times successively with tetrahydrofuran and anhydrous ethanol, and then dried in a vacuum drying oven at 60 ℃ for 24 h, finally yielding a series of powdered IL-COFs containing different functional groups. The types of amino monomers, aldehyde monomers, and ILs corresponding to the different IL-COFs are shown in Table 1.

[0057] Table 1. Preparation of IL-COFs

[0058]

[0059] Characterization of the prepared series of IL-COFs as follows Figure 2 As shown, the infrared spectrum shows the values ​​in the 1616-1618 cm⁻¹ range. -1 The presence of a characteristic peak indicating a C=N bond at the point suggests that the synthesized IL-COFs all contain imine bonds and have undergone a Schiff base condensation reaction. Figure 2 a). Powder X-ray diffraction patterns of the synthesized IL-COFs indicate that IL ([BMIM][Tf2N]) -COF (TAPB-OMeTA) IL ([BMIM][Tf2N]) -COF (TAPT-OMeTA) IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) IL ([HMIM][Tf2N]) -COF (TAPT-BrTA) Obvious diffraction peaks are observed at 2.75°, 2.85°, 2.88° and 2.85° respectively, which are attributed to the (100) crystal plane. Figure 2 b). However, the type of monomer and the type of ILs also affect the crystallization of IL-COFs. ([BMIM][BF4]) -COF (TAPT-BrTA) and IL ([BMIM][Tf2N]) -COF (TAPT-OHTA) Powder X-ray diffraction patterns indicate that the IL-COFs synthesized under these reaction conditions have poor crystallinity. Figure 2 c and 2d).

[0060] 2. Screening of covalent organic framework materials synthesized by ionic liquid catalysis

[0061] This study primarily investigates the effects of covalent organic frameworks (COFs) synthesized from different amino monomers (TAPB and TAPT), aldehyde monomers (OMeTA, BrTA, and OHTA), and IL types ([BMIM][Tf2N], [HMIM][Tf2N], and [BMIM][BF4]) on the adsorption efficiency of target analytes. IL-COFs were used as adsorbents to adsorb two AFs (B1 and G1, representing AFs) and their three precursors OMST, AVN, and ST. The specific operational steps are as follows:

[0062] Accurately weigh 0.5 mg of IL-COFs material and add it to 10 mL of a mixed standard solution of five analytes (two AFs (B1 and G1) and their three precursors OMST, AVN, and ST) at a concentration of 100 ng / mL. Sonicate for 2 min, shake at 220 rpm for 8 min, and centrifuge at 10,000 rpm for 5 min. Filter the supernatant through a 0.22 μm PTFE membrane and analyze the concentration of the five analytes in the solution using UHPLC-MS / MS.

[0063] The adsorption efficiencies were compared, and the results are as follows: Figure 3 As shown.

[0064] from Figure 3 As can be seen, when [BMIM][Tf2N] is used as the solvent and catalyst, the optimal amino and aldehyde monomers for synthesizing COFs are TAPT and BrTA, respectively. When OMeTA is used as the aldehyde monomer, IL-COFs synthesized with the amino monomer TAPT have higher adsorption efficiency for the target analytes than those synthesized with the amino monomer TAPB. When TAPT is used as the amino monomer, IL-COFs containing -Br have higher adsorption efficiency for the five target analytes than those containing -OMe and -OH. This may be because -Br has strong electronegativity and can act as an electron-withdrawing group, and the synthesized IL-COFs have higher adsorption efficiency for the target analytes. ([BMIM][Tf2N]) -COF (TAPT-BrTA) It has good crystallinity.

[0065] from Figure 3 b shows that when TAPT and BrTA are used as amino and aldehyde monomers respectively, and [BMIM][Tf2N] is used as the reaction solvent and catalyst, the synthesized IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The highest adsorption efficiency was observed for the target analyte. Increasing the carbon chain length of the imidazole cation (from C4 to C6) did not change the adsorption efficiency of the synthesized IL-COFs for the target analyte. This may be because the slight increase in the alkyl carbon chain length did not significantly alter the solubility of the monomer in the ILs. When the anion of the ILs changed from [Tf₂N]... - Change to [BF4] - Synthetic IL ([BMIM][BF4]) -COF (TAPT-BrTA) The adsorption efficiency for the target analyte was significantly reduced. This was due to the low catalytic efficiency of the strongly alkaline [BMIM][BF4], and also because ILs are hygroscopic, leaving a small amount of moisture even after thorough drying. Water reacts with [BF4]. - The hydrofluoric acid produced in the reaction catalyzes the decomposition of ILs over time, while the anion is selected from [Tf₂N]. - This can avoid the effects of hydrofluoric acid on ILs.

[0066] The prepared IL with the best adsorption efficiency ([BMIM][Tf2N]) -COF (TAPT-BrTA) The characteristics such as Figure 4 As shown, IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) It possesses an extremely high BET specific surface area (1435.3 m² / g) and a large pore volume of 1.10 cm³. 3 / g, the material exhibits a distinct Type IV isotherm ( Figure 4a) contains micropores with a diameter of 1.0 nm and mesopores with a diameter of 2.2 nm. Figure 4 b). Scanning electron microscopy shows IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) It is in the form of long, clustered strips. Figure 4 c) C, N, Br, and F elements are present and uniformly distributed throughout the IL-COFs. ([BMIM][Tf2N]) -COF (TAPT-BrTA) Contains fluorine (0.21wt%) Figure 4 d), this is due to the in-situ encapsulation of a small amount of [BMIM][Tf2N] during the synthesis of IL-COFs, which was not removed even after repeated washing with organic solvents. The presence of fluorine allows the adsorbent to specifically adsorb AFs and their precursors through multiple interactions such as FO and F-π. High-resolution transmission electron microscopy revealed a large number of ordered porous structures and layered lattice fringes, fully demonstrating the high crystallinity of the material. The measured lattice spacing was 0.35 nm. Figure 4 e). In 13 C solid-state nuclear magnetic resonance spectrum ( Figure 4 In f), the signal at 156 ppm corresponds to the carbon atom of the imine bond, confirming the successful Schiff base condensation reaction catalyzed by ILs, and the preparation of imine-type ILs. ([BMIM][Tf2N]) -COF (TAPT-BrTA) .

[0067] 3. Effect of reaction time on IL-COFs

[0068] This embodiment mainly studies the effect of condensation reaction time on the synthesis of IL-COFs. Specifically, this embodiment uses highly crystalline IL-COFs as an example. ([BMIM][Tf2N]) -COF (TAPT-BrTA) To conduct time-dependency experiments on objects, the steps are as follows:

[0069] TAPT (56.4 μmol), BrTA (84.6 μmol), and 1 mL of [BMIM][Tf₂N] were mixed and magnetically stirred for 10 min. Then, 0.2 mL of acetic acid aqueous solution (6 mol / L) was added, and stirring was continued for 1 min to form a homogeneous dispersion. The mixture was allowed to stand at room temperature for 30 min, 1 h, 3 h, 6 h, 12 h, and 24 h, respectively. The solid products obtained at different reaction times were collected, washed three times sequentially with tetrahydrofuran and anhydrous ethanol, and then dried in a vacuum drying oven at 60 ℃ for 24 h, finally yielding ILs obtained at a series of reaction times. ([BMIM][Tf2N]) -COF (TAPT-BrTA) Powder X-ray diffraction analysis was performed.

[0070] Powder X-ray diffraction pattern ( Figure 5 The results showed that the diffraction peaks corresponding to the (100) crystal plane appeared and grew rapidly within 30 min, and the crystal structure was improved and tended to stabilize after 1 h, indicating that the use of [BMIM][Tf2N] as a solvent accelerated the rapid crystallization of COFs materials, and IL could be synthesized in 1 h. ([BMIM][Tf2N]) -COF (TAPT-BrTA) .

[0071] Example 2: IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Fibers used as coatings for solid-phase microextraction (SPME) preparation

[0072] This embodiment uses IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The specific steps for preparing SPME fibers as an SPME coating in this embodiment are as follows:

[0073] A stainless steel wire (500 μm in diameter and 9 cm in length) was ultrasonically cleaned sequentially with methanol, acetone, and ultrapure water. The cleaned stainless steel wire was then coated with a layer of polyacrylonitrile (PAN) adhesive and immediately immersed in a solid IL. ([BMIM][Tf2N]) -COF (TAPT-BrTA) A uniform coating was formed on the powder and cured in an oven at 80 °C for 30 min. This process was repeated 6 times. Finally, the SPME fiber was coated with a layer of polyacrylonitrile (PAN) adhesive and cured in an oven at 80 °C for 12 h. Excess coating was removed with a knife, leaving a 1.8 cm length of coating on the wire. The SPME fiber was then immersed in static N,N-dimethylformamide (3 mL) for 6 min at room temperature to remove excess polyacrylonitrile (PAN) adhesive from the fiber surface. It was then washed with methanol and ultrapure water, dried, and coated with IL. ([BMIM][Tf2N]) -COF (TAPT-BrTA) SPME fibers, i.e., IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Coated fiber.

[0074] The resulting coating with COF-IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Scanning electron microscopy of SPME fibers, such as Figure 6 As shown in the image, the SPME fiber surface is uniform ( Figure 6 a) The diameter of the coated fiber is approximately 1460 μm. Subtracting the diameter of the stainless steel wire (500 μm), the thickness of the coating is calculated to be approximately 480 μm. Figure 6 The magnified image of the fiber coating in b shows that the adhesion of the polyacrylonitrile (PAN) adhesive was not altered. ([BMIM][Tf2N]) -COF (TAPT-BrTA) Clustered morphology.

[0075] Example 3: Experimental study on different extraction times, types of desorbents, and desorption times

[0076] This embodiment primarily studies the effects of extraction time, desorbent type, and desorption time on extraction recovery. The sample solution mentioned in this embodiment refers to a spiked peanut sample solution, prepared as follows:

[0077] The blank peanut sample was crushed, and 2.0 g of the sample was weighed. 200 ng / g of 4 AFs (B1, B2, G1, G2) and 7 mixed standards of their 3 precursors OMST, AVN and ST were added. 8 mL of acetonitrile / water (80:20, v / v) solution was added, vortexed for 2 min, and ultrasonically extracted for 10 min. After centrifugation at 10000 rpm for 5 min, 4 mL of supernatant was transferred and concentrated to near dryness by nitrogen blowing at 60 ℃. 10 mL of primary water was added to redissolve the residue to obtain a peanut sample solution containing 7 target analytes.

[0078] 1. Experimental study on different extraction times

[0079] Acetone was used as the desorbent, and the extraction times were 20 min, 30 min, 40 min, 50 min, and 60 min, respectively. The specific operating steps are as follows:

[0080] The IL-coated material prepared using the method in Example 2 will be used. ([BMIM][Tf2N]) -COF (TAPT-BrTA) SPME fibers were immersed in 10 mL of peanut sample solution. Adsorption was performed by shaking at 220 rpm for 20 min, 30 min, 40 min, 50 min, and 60 min, respectively. The SPME fibers were then removed, gently wiped with filter paper, and immersed in an inner tube containing 300 μL of acetone. Desorption was carried out by shaking for 5 min. The eluent containing the analyte was then concentrated to near dryness under a gentle nitrogen flow and redissolved in 100 μL of methanol. The solution was filtered through a 0.22 μm PTFE membrane and analyzed by UHPLC-MS / MS.

[0081] The extraction recovery rates obtained at different extraction times were compared, and the results are as follows: Figure 7 As shown in a.

[0082] from Figure 7 As shown in Figure a, when the extraction time increased from 20 min to 50 min, the peak areas of the seven target compounds continuously increased and reached their peak values ​​at 50 min. With further increases in extraction time, the peak areas tended to stabilize. This indicates that extraction equilibrium can be achieved at 50 min.

[0083] 2. The effect of desorbent type on extraction efficiency

[0084] The extraction time was 50 min, and the desorbents were methanol, ethanol, acetonitrile, ethyl acetate, and acetone. The specific operating steps are as follows:

[0085] The IL-coated material prepared using the method in Example 2 will be used. ([BMIM][Tf2N]) -COF (TAPT-BrTA) SPME fibers were immersed in 10 mL of peanut sample solution. Adsorption was performed by shaking at 220 rpm for 50 min. The SPME fibers were then removed, gently wiped with filter paper, and subsequently immersed in inner tubes containing 300 μL each of methanol, ethanol, acetonitrile, ethyl acetate, and acetone, respectively. Desorption was performed by shaking for 5 min. The eluent containing the analyte was then concentrated to near dryness under a gentle nitrogen flow and redissolved in 100 μL of methanol. The solution was filtered through a 0.22 μm PTFE membrane and analyzed by UHPLC-MS / MS.

[0086] The extraction recoveries obtained using different desorbents were compared, and the results are as follows: Figure 7 As shown in b.

[0087] from Figure 7 As shown in b, acetone has the highest extraction efficiency for the seven target compounds when used as a desorbent. This may be because acetone, which contains unsaturated carbonyl groups, has stronger hydrophobicity than methanol, ethanol, acetonitrile, and ethyl acetate, and can effectively disrupt the π-π and hydrophobic interactions between the target compounds and the adsorbent.

[0088] 3. Experimental study on different desorption times

[0089] The extraction time was 50 min, and acetone was used as the desorption agent. The desorption times were 5 min, 10 min, 15 min, 20 min, and 25 min, respectively. The specific operating steps are as follows:

[0090] The IL-coated material prepared using the method in Example 2 will be used. ([BMIM][Tf2N]) -COF (TAPT-BrTA) SPME fibers were immersed in 10 mL of peanut sample solution. Adsorption was performed by shaking at 220 rpm for 50 min. The SPME fibers were then removed, gently wiped with filter paper, and then immersed in an inner tube containing 300 μL of acetone for desorption by shaking for 5 min, 10 min, 15 min, 20 min, and 25 min, respectively. The eluent containing the analyte was then concentrated to near dryness under a gentle nitrogen flow and redissolved in 100 μL of methanol. The solution was filtered through a 0.22 μm PTFE membrane and analyzed by UHPLC-MS / MS.

[0091] The extraction recovery rates obtained at different resolution times were compared, and the results are as follows: Figure 7 As shown in c.

[0092] from Figure 7 As shown in Figure c, the peak areas of all analytes did not change significantly with increasing desorption time during the tested desorption period, indicating that complete desorption can be achieved in 5 minutes.

[0093] Example 4: IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Memory effect of coated fibers

[0094] This embodiment mainly examines IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The memory effect of coated fibers. The specific operation steps in this embodiment are as follows:

[0095] The IL prepared using the method in Example 2 ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coated fibers were immersed in a peanut sample solution containing seven analytes prepared according to the method in Example 3. The solution was shaken at 220 rpm for 50 min for adsorption. The SPME fibers were then removed, gently wiped with filter paper, and then immersed in an inner tube containing 300 μL of acetone. The solution was shaken for 5 min for desorption. The eluent containing the analytes was then concentrated to near dryness under a gentle nitrogen flow and redissolved in 100 μL of methanol. The solution was filtered through a 0.22 μm PTFE membrane and analyzed by UHPLC-MS / MS. The used fibers were washed sequentially with methanol and ultrapure water for 30 min each, dried, and then immersed again in an inner tube containing 300 μL of acetone, repeating the above desorption steps.

[0096] The ratio of the peak area of ​​the target analyte in the second desorption to that in the first desorption was used to investigate the IL. ([BMIM][Tf2N]) -COF (TAPT-BrTA) The memory effect of coated fibers, the result is as follows Figure 8 As shown.

[0097] from Figure 8 As can be seen, IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) In the second desorption of the coated fiber, the peak areas of all target substances were less than 8.8% of those in the first desorption, indicating that the desorption was complete and the memory effect was negligible.

[0098] Example 5: IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Comparison of coated fibers and commercial fibers

[0099] This embodiment mainly compares the IL prepared using the method of Example 2. ([BMIM][Tf2N]) -COF (TAPT-BrTA)The extraction performance of the coated fiber and three commercially available DVB / CAR / PDMS fibers (50 / 30 μm), CAR / PDMS fiber (75 μm), and PDMS / DVB fiber (65 μm) (all purchased from Supelco, USA) on the target analyte was compared. The specific operating steps in this example are as follows:

[0100] IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Coated fibers, DVB / CAR / PDMS fibers (50 / 30 μm), CAR / PDMS fibers (75 μm), and PDMS / DVB fibers (65 μm) were immersed in a peanut sample solution prepared according to the method in Example 3. The solution was shaken at 220 rpm for 50 min to adsorb the analyte. The SPME fibers were then removed, gently wiped with filter paper, and then immersed in an inner tube containing 300 μL of acetone. The solution was shaken for 5 min to desorb the analyte. The eluent containing the analyte was then concentrated to near dryness under a gentle nitrogen flow and redissolved in 100 μL of methanol. The solution was filtered through a 0.22 μm PTFE membrane and analyzed by UHPLC-MS / MS.

[0101] Enrichment factors (EFs), i.e., the ratio of the target analyte concentration in the desorption solution after SPME to the initial concentration added to the sample, were used to compare the extraction performance of the fiber. Results are as follows: Figure 9 As shown.

[0102] from Figure 9 As can be seen, IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coated fibers exhibited excellent extraction capabilities, with EFs ranging from 40.1 to 81.0, which are 8.4 to 32.1 times, 7.3 to 10.8 times, and 3.9 to 9.2 times that of DVB / CAR / PDMS fibers, PDMS / DVB fibers, and CAR / PDMS fibers, respectively. This is likely because, compared to commercially available fiber coatings, IL... ([BMIM][Tf2N]) -COF (TAPT-BrTA) It possesses a large specific surface area and hierarchical porosity, and its structure contains a large number of π-electron systems and abundant bromine atoms that can act as electron-withdrawing groups. It can adsorb target substances through electrostatic interactions, hydrophobic interactions, π-π interactions and size matching effects. In addition, [BMIM][Tf2N] is encapsulated inside the material, and the presence of fluorine can provide more interaction sites and interactions for the simultaneous and efficient extraction of AFs and their precursors.

[0103] Example 6: IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Reusability of coated fibers

[0104] This embodiment mainly examines the IL prepared using the method of Example 2.([BMIM][Tf2N]) -COF (TAPT-BrTA) The reusability of the coated fibers. The specific operating steps in this embodiment are as follows:

[0105] Following the extraction steps in Example 5, the same IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The peak areas of the target compounds in the peanut sample solution prepared by the method in Example 3 were analyzed by UHPLC-MS / MS after each extraction using the repeated extraction of the coated fiber.

[0106] The results are as follows Figure 10 As shown, after 30 repeated uses, IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coated fibers reduced the peak area of ​​seven target compounds by 7.0%–15.1%, indicating that IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coated fibers exhibit excellent stability and can be reused at least 30 times. Meanwhile, during this process, IL... ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coated fibers can withstand multiple adsorption-desorption operations without damage, demonstrating excellent durability and great application potential in the extraction of trace target substances in real samples.

[0107] Example 7: IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Performance evaluation of SPME-UHPLC-MS / MS method for determining four AFs (B1, B2, G1, G2) and their three precursors OMST, AVN, and ST in peanut samples, and its application in actual peanut samples.

[0108] IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The specific method for determining four AFs (B1, B2, G1, G2) and their three precursors OMST, AVN, and ST in peanut samples using SPME-UHPLC-MS / MS is as follows:

[0109] The peanut sample was crushed, and 2.0 g of the sample was weighed. 8 mL of acetonitrile / water (80:20, v / v) solution was added, vortexed for 2 min, and ultrasonically extracted for 10 min. The mixture was then centrifuged at 10000 rpm for 5 min, and 4 mL of the supernatant was collected. The supernatant was concentrated to near dryness under nitrogen blowing at 60 °C. 10 mL of primary water was added to redissolve the residue to obtain the sample solution. Then, the IL prepared using the method in Example 2 was... ([BMIM][Tf2N]) -COF (TAPT-BrTA) The coated fiber was immersed in the sample solution and shaken at 220 rpm for 50 min to adsorb the sample. The IL was then removed. ([BMIM][Tf2N]) -COF (TAPT-BrTA)The coated fiber was gently wiped with filter paper and then immersed in an inner tube containing 300 μL of acetone. The solution was shaken and desorbed for 5 min. The eluent containing the analytes was then concentrated to near dryness under a gentle nitrogen flow and redissolved in 100 μL of methanol. The solution was filtered through a 0.22 μm PTFE membrane, and the contents of four AFs (B1, B2, G1, G2) and their three precursors OMST, AVN, and ST were determined by UHPLC-MS / MS.

[0110] The mass spectrometry parameters of the above seven target compounds are shown in Table 2.

[0111] Table 2. Physicochemical properties and MS / MS parameters of the seven target compounds.

[0112]

[0113] IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) The analytical performance of the SPME-UHPLC-MS / MS method in peanut samples is shown in Table 3.

[0114] Table 3, IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) Analytical performance of SPME-UHPLC-MS / MS method in peanut samples

[0115]

[0116] The method of this invention exhibits good linearity (R0) in the range of 0.015-200 ng / g. 2 ≥ 0.9951). The limits of detection and limits of quantitation for the seven target analytes in peanut samples were 0.005–0.015 ng / g and 0.015–0.05 ng / g, respectively. The intra-day (n = 5) and inter-day (n = 3) precision for the seven target analytes were both less than 5.3%. Meanwhile, three parallel IL-1000 samples... ([BMIM][Tf2N]) -COF (TAPT-BrTA) The inter-fiber precision of the coated fibers is 3.9%-7.1% (n = 3). The matrix effect of the method is 87.2%-109.1%. This indicates that the method of the present invention has high sensitivity and good repeatability, with a small matrix effect.

[0117] After crushing the peanut sample, 2.0 g of the sample was weighed and spiked with AFs (B1, B2, G1, G2), OMST, AVN, and ST at concentrations of 0, 2, 10, and 50 ng / g, respectively. The sample was processed according to the above method. Three parallel measurements were performed for each spiked sample, and the average value was taken. The spiked recovery rate was calculated based on the actual amount added and the measured results. The results are shown in Table 4. A representative chromatogram of the spiked peanut sample after SPME is shown below. Figure 11 As shown.

[0118] Table 4, IL ([BMIM][Tf2N]) -COF (TAPT-BrTA) -SPME-UHPLC-MS / MS detection of AFs and their precursors in peanuts (n=3)

[0119]

[0120] In Table 4, peanut 1: Da Bai Sha; peanut 2: Yu Hua 23; peanut 3: Yuan Za 6; ND: Not detected; SD: Standard deviation.

[0121] The results showed that 4.7 ng / g of AFB1 and 2.1 ng / g of AFB2 were detected in peanut sample 2, while the rest were not detected. Furthermore, the recoveries of the spiked samples ranged from 80.1% to 106.4%, and the precision was less than 8.6% for all samples. The experimental results indicate that the established analytical method has satisfactory accuracy and repeatability and can be used to determine AFs (B1, B2, G1, G2), OMST, AVN, and ST in peanut samples from different varieties.

[0122] Example 8: Dynamic changes in the content of AFs and their precursors in stored peanuts and early warning strategies based on AFs precursors

[0123] Select peanuts with intact appearance and autoclave them at 121 °C for 20 min. Dilute the Aspergillus flavus spore suspension with sterile water at a ratio of 4 mL / 100g, mix thoroughly, and inoculate the peanuts at an inoculation rate of 5 × 10⁶. 5 Peanuts were inoculated at spore count / g and stored at 4 °C for 24 h, stirring with a glass rod every 8 h to ensure uniform rehydration. Then, 25 g of this peanut sample was placed in sterile petri dishes (9 cm in diameter) and placed in a desiccator containing saturated ammonium sulfate solution. The dishes were incubated at 28 °C in the dark for 7 days. Samples were taken every 12 h after inoculation, and all collected peanut samples were stored at -20 °C until extraction. The cultured moldy peanut samples were pulverized and ground with liquid nitrogen. Peanut samples not inoculated with Aspergillus flavus were used as blank samples. The IL method described in Example 7 was employed. ([BMIM][Tf2N]) -COF (TAPT-BrTA) -SPME-UHPLC-MS / MS was used to detect the contents of AFs (B1, B2, G1, G2), OMST, AVN, and ST. The experiment was conducted in triplicate. A photograph of peanut samples artificially infected with Aspergillus flavus stored for 7 days in a constant temperature and humidity environment is shown below. Figure 12 As shown in the figure. The dynamic changes and correlation analysis heatmaps of AFs and their precursors are shown in the figure. Figure 13 and Figure 14 As shown.

[0124] The dynamic changes of AFs and their precursors show that ( Figure 13 Under suitable conditions, peanuts quickly become moldy and produce amylopectin (AFs) and their precursors. On day 1, only AVN (0.14 ng / g) was detected. On day 1.5, trace amounts of AFB1 (0.4 ng / g), AFB2 (0.13 ng / g), and OMST (0.25 ng / g) were detected for the first time; at this point, mycelium was not yet observed on the peanut surface. On day 2, the AFB1 concentration was 2.50 ng / g, while on day 2.5, the AFB1 concentration increased to 40.20 ng / g, exceeding the maximum residue limits (MRLs) set by China and the United States (< 20 ng / g). At this point, obvious white mycelium was visible on the peanut surface. Figure 12 On the same day, the AFB2 concentration was 1.2 ng / g, while AFG1 and AFG2 were not yet detected, confirming that AFB1 was the predominant AFs produced, representing the main metabolic pathway of *A. flavus*. The precursor ST was first detected on day 2 (1.10 ng / g). Since AVN was first detected on day 1, and the concentrations of AFB1 and the sum of the four AFs all exceeded MRLs on day 2.5, it can be preliminarily inferred that AVN can predict AF contamination in stored peanuts 1.5 days in advance.

[0125] Heat map ( Figure 14The results showed that ST and OMST, as key precursors appearing successively in the AFB1 and AFG1 branch pathways, were significantly correlated in content (Pearson's = 0.79), and were also positively correlated with AFB1 and AFG1, with higher correlations than with AFB2 and AFG2. This result is consistent with the metabolic pathway of *A. flavus*. During peanut storage, AVN was detected only three times, and its content was negatively correlated with all four AFs (B1, B2, G1, and G2) (Pearson's = -0.25 to -0.36). Throughout the peanut mold growth process, AVN was detected first. The contents of AVN, ST, and OMST initially increased and then decreased, reaching peak values ​​on days 1.5, 3.5, and 4.5, respectively. Four aerosol oxidases (AFs) (B1, B2, G1, and G2) peaked on day 6. OMST showed the highest correlation with AFs, followed by ST. However, OMST and AFB1 were detected for the first time at the same time, with only a 1.5-day difference in peak value, indicating a narrow warning window. Furthermore, compared to the mold growth process in corn, the peanut mold growth process was much faster under the same storage conditions, posing greater challenges to AF contamination warning in peanuts. Therefore, to fully ensure the timeliness and accuracy of precursors as warning indicator molecules, the performance of warning detection methods should be improved to simultaneously, accurately, and sensitively detect as many precursors as possible. By comprehensively analyzing the first appearance time, peak time, and corresponding concentration of precursors and AFs, combined with the characteristics of the actual sample matrix, the degree of AF contamination can be predicted, allowing more time for AF contamination prevention.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A covalent organic framework material synthesized based on ionic liquid catalysis, characterized in that, The preparation method of the covalent organic framework material includes: adding an aqueous acetic acid solution to a mixture of an amino monomer, an aldehyde monomer and an imidazole ionic liquid, mixing well, and then allowing the mixture to stand at room temperature, normal pressure and open environment to react and obtain the covalent organic framework material.

2. The covalent organic framework material synthesized based on ionic liquid catalysis according to claim 1, characterized in that, The amino monomer is 2,4,6-tris(4-aminophenyl)-1,3,5-triazine or 1,3,5-tris(4-aminophenyl)benzene; The aldehyde monomer is 2,5-dibromophenyl-1,4-dicarboxaldehyde, 2,5-dihydroxy-1,4-benzenedicarboxaldehyde, or 2,5-dimethoxyphenyl-1,4-dicarboxaldehyde; The imidazole-based ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, or 1-butyl-3-methylimidazolium tetrafluoroborate.

3. The covalent organic framework material synthesized based on ionic liquid catalysis according to claim 1, characterized in that, The molar ratio of the amino monomer, aldehyde monomer, and acetic acid is 1:1.5:21.3, the ratio of the amino monomer to the imidazole ionic liquid is 56.4 μmol:1 mL, and the reaction time is more than 1 hour.

4. A solid-phase microextraction fiber, characterized in that, The solid-phase microextraction fiber refers to a stainless steel wire coated with the covalent organic framework material as described in any one of claims 1-3.

5. The method for preparing solid-phase microextraction fibers according to claim 4, characterized in that, The covalent organic framework material according to any one of claims 1-3 is coated onto the surface of a stainless steel wire with an adhesive and then cured by heating.

6. The application of the covalent organic framework material according to any one of claims 1-3 and the solid-phase microextraction fiber according to claim 4 in the detection of aflatoxin and / or aflatoxin precursors.

7. The application according to claim 6, characterized in that, The aflatoxin is aflatoxin B1, B2, G1 and / or G2, and the aflatoxin precursor is averantine, aflatoxin and / or O-methylaflatoxin.

8. The application according to claim 6, characterized in that, The detection includes: extracting aflatoxin and / or aflatoxin precursor from the sample, obtaining a sample extract, performing solid-phase microextraction on the aflatoxin and / or aflatoxin precursor in the sample using the solid-phase microextraction fiber as described in claim 4, and then analyzing it using ultra-high performance liquid chromatography-mass spectrometry to obtain quantitative results of aflatoxin and / or aflatoxin precursor.

9. The application according to claim 8, characterized in that, The extraction time in the solid-phase microextraction process is 20–60 min, and the desorbent is methanol, ethanol, acetonitrile, ethyl acetate or acetone, with a desorption time of 5–25 min.

10. A method for early warning of aflatoxin contamination, characterized in that, Quantitative detection of aflatoxin precursors in samples is used to provide early warning of aflatoxin contamination in samples. The quantitative detection includes: extracting aflatoxin precursors from the sample to obtain a sample extract; performing solid-phase microextraction on the aflatoxin precursors in the sample using the solid-phase microextraction fiber described in claim 4; and then analyzing the extract using ultra-high performance liquid chromatography-mass spectrometry to obtain quantitative results of the aflatoxin precursors.

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