Construction Of Novel Covalent Organic Framework Materials And Their Application In The Determination Of Animal-derived Food Contaminants

Food safety is of vital importance to the national economy and people's livelihood and has become a significant public safety issue.The animal-derived food occupies a considerable proportion of in daily diet,and it is easier to accumulate toxic and harmful substances.Thus,it is particularly important to ensure the safety of animal-derived food.Fast and accurate food safety detection technology is a powerful tool to realize the effective monitoring of animal-derived food contaminants.However,the required sensitivity or accuracy cannot be achieved with instruments detection directly due to the complexity of the food matrix and the extremely low concentration of analytes.Therefore,it is necessary to use appropriate sample preparation technologies to extract and enrich target analytes for improvement the accuracy of analysis and detection methods.Recently,several sample preparation technologies based on adsorbent materials have been developed and successfully applied to the extraction and enrichment of food contaminants.The adsorbent material is the key of sample preparation technology.Covalent organic frameworks not only overcome the shortcomings of poor selectivity and low adsorption of traditional adsorbents but also show great potential in the field of adsorption and separation for food contaminants due to its high porosity,large specific surface area,diverse structure,and easy modification.On the basis of the imine-linked COFs and the analysis object,this dissertation designed and prepared four covalent organic frameworks-based composite materials.These composite materials were used as adsorbents in sample preparation technology to achieve selective extraction for animal-derived food contaminants.Further combining with chromatography technology,rapid and accurate detection methods for contaminants in animal-derived foods have been constructed.The main research contents are as follows:(1)The magnetic covalent organic framework-metal organic framework composite materials(Fe3O4@TbBd@ZIF-8)were designed and prepared.The synthesized magnetic Fe3O4@TbBd@ZIF-8 composite materials were used as adsorbents for magnetic solid phase extraction of sedatives in meat samples.Further combining with liquid chromatography-mass spectrometry,an extraction and detection method was constructed for sedatives in meat samples.The factors affecting the extraction performance of magnetic solid phase extraction were optimized.The adsorption behavior of Fe3O4@TbBd@ZIF-8 to sedatives conformed to the pseudo-second order model and Freundlich isotherm model,and further it is spontaneous.Under the optimum conditions,the limits of detection(LODs)of sedatives in bovine and chicken samples are 0.3-0.8 ?g kg-1 and 0.3-0.7?g kg-1,respectively,and the recovery of the method was 83.8%-105.4%.The method had good sensitivity and accuracy,satisfying the residue determination of sedatives in meat samples.(2)A type of covalent organic framework foam(TbBd-foam)with heterogeneous pores was prepared by combining mechanochemical synthesis and gas foaming technology.It was used as an adsorbent for dispersive solid phase extraction of malachite green and crystal violet antibacterial agent.Further combining with high performance liquid chromatography,an extraction and detection method was constructed for malachite green and crystal violet antibacterial agent in fish samples.During the synthesis of TbBd-foam,the generated carbon dioxide overflowed through the COFs to form heterogeneous pores and interconnected pores,which increased mass transfer rate.The adsorption behavior of TbBd-foam on malachite green and crystal violet antibacterial agents was explored in terms of adsorption kinetics,adsorption isotherms and adsorption thermodynamics.Compared with TbBd-COF synthesized by the same monomer at room temperature,TbBd-foam took less time to reach adsorption equilibrium and had higher adsorption capacity than that of TbBd-COF.Under the optimum conditions,the LODs of malachite green and crystal violet antibacterial agents in carp and grass carp samples were 0.2-0.3 ?g kg-1.The established method had good accuracy(in the range of 92.5-106.7%)and precision(RSD?7.1%).(3)A kind of solid phase microextraction fiber was prepared with COF(TpDA)as coating material.The fiber was used as adsorbent to extract endocrine disrupting chemicals in meat samples by solid phase microextraction.Further combining with gas chromatography electron capture detector,an extraction and detection method was construct for endocrine disrupting chemicals in meat samples.In order to ensure the extraction efficiency of TpDA coated fibers for target analytes,the main SPME extraction conditions and derivatization conditions were optimized,including temperature,extraction time,pH,ionic strength,eluent,desorption time,and derivatization conditions.The TpDA coated fiber adsorbed endocrine disrupting chemicals through the ?-? interaction,the hydrophobic interaction,electrostatic interaction and hydrogen bonding.Under the optimal experimental conditions,the LODs of fish and pork samples were 1.1-1.5?g kg-1 and 1.2-1.5 ?g kg-1,respectively.The recovery of the method ranged from 83.1%to 108.3%with RSD less than 10.2%,which implied that the method had good stability.(4)A type of novel covalent organic framework composite material(MS@PDA@TAPB-DMTA)was designed and prepared by using melamine sponge(MS)as substrate material.The MS@PDA@TAPB-DMTA was used as adsorbent to prepare a miniaturized pipette-tip solid phase extraction device with low cost,which was applied to extract sulfonamides in meat samples.The detection method was established for sulfonamides in meat samples by combining with gas chromatography electron capture detector.As the base material,the three-dimensional network structure of melamine sponge can effectively prevent the aggregation of COFs particles and high backpressure.The factors affecting the extraction performance of pipette-tip solid phase extraction were optimized.Under the optimized conditions,the LODs of pork and bovine samples were 1.7-2.6 ?g kg-1 and 1.9-2.7 ?g kg-1,respectively.The recovery of method ranged from 81.6%to 104.9%.The as-synthesized pipette-tip solid phase extraction device had several advantages,including simple structure,easy to assemble and operate and excellent extraction performance,which displayed good potential for extraction and determination of food contaminants.Based on animal-derived food contaminants as analytes,four covalent organic framework composite adsorbents were prepared applied to the preparation process of animal-derived food samples,which realized the selective extraction and efficient purification of target analytes,improved the sensitivity of subsequent chromatographic detection and improved the accuracy of analytical detection methods.