Research On Post-modification Of ZIF-8 With Amine For Preparation Of Chemical Bonded Monolithic Column And Its Extraction Application

Monolithic column are organic,inorganic or organic-inorganic hybrid in-situ polymerized monolithic materials.Among them,the organic polymer monolithic column,as a solid phase microextraction（SPME）adsorbent,has attracted much attention due to its simple preparation,good permeability,biocompatibility,p H stability and easy surface modification.However,the unsatisfactory specific surface area and adsorption sites of the monolithic column will result in poor separation and enrichment effects.Choosing appropriate materials to chemically modify the monolithic column to increase the specific surface area of the polymer and improve the adsorption site is an effective way to improve its separation and enrichment performance.Metal organic frameworks（MOFs）are a kind of network framework structure formed by the self-assembly of metal ions and organic ligands through coordination.The material has a large number of mesopores and small pores and has a large specific surface area,and the adsorption sites on the surface have a good molecular recognition effect.Among them,the zeolite imidazole framework（ZIF）material has a large specific surface area and good thermal stability,water stability and chemical stability.Among them,the cubic sodalite framework ZIF-8 is connected with Zn²⁺by a 2-methylimidazole ligand.It has the characteristics of permanent porosity,easy synthesis and modification.It is an ideal material for chemical modification of monolithic column surface.ZIF-8 modified polymer monolithic column has the advantages of MOF and monolithic column material,and is expected to improve the performance of the monolithic column material SPME.Most of the properties of MOFs depend on their special functional groups.Generally,MOFs are synthesized by solvothermal method,but most functional groups cannot exist stably under solvothermal conditions.Therefore,the modification of MOFs by post-synthesis modification method can solve the above-mentioned problems and avoid the occurrence of competitive reactions during the synthesis of MOFs.In this paper,post-synthesis modification method was used to functionalize ZIF-8,and then ZIF-8 modified polymer monolithic column and ZIF-8 copolymer monolithic column were prepared by chemical bonding.Using the adsorption performance of the ZIF-8 modified monolithic column and applying it to solid phase microextraction,a solid phase microextraction-high performance liquid chromatography（SPME-HPLC）quantitative analysis method of phenanthrene（PHE）,fluoranthene（FLT）and pyrene（PYR）in cereal samples was established.The main content includes the following two aspects:（1）Using ZIF-8 with a uniform internal cavity structure and large specific surface area as a functional material,an organic polymer monolithic column composite material was prepared by chemical bonding.The post-synthesis amino modification of ZIF-8 is used as the modified material for the monolithic column,methacrylic acid（MAA）as the functional monomer,ethylene glycol dimethacrylate（EGDMA）as the crosslinking agent,and methanol as the porogen,the ZIF-8 poly（MAA-EGDMA）monolithic column was prepared.Scanning electron microscopy,powder X-ray diffraction,fourier transform infrared spectroscopy,thermogravimetric analysis and specific surface area were used to determine the physical morphology and chemical structure of the ZIF-8 polymer monolithic column,and the adsorption performance was studied.The results of adsorption experiments show that the ZIF-8 poly（MAA-EGDMA）monolithic column has good adsorption selectivity for three PAHs of PHE,FLT and PYR,with adsorption capacities of 6.90,5.50 and 5.60 mg·g^–1,respectively.Under the premise of ensuring the recovery rate of quantitative analysis,it can be reused at least 50 times,indicating that the monolithic column has good adsorption reproducibility and service life.The material was applied to solid-phase microextraction,and under optimized extraction conditions,a SPME-HPLC separation and analysis method for PHE,FLT and PYR in soybean samples was established.The linear range of this method for PHE and PYR was 1.5～800μg·kg^–1,the linear range for FLT was 2.5～800μg·kg^–1,the correlation coefficient（R²）was greater than 0.99,the detection limit（LODs,S/N=3）was0.38～0.76μg·kg^–1,the limit of quantification（LOQs,S/N=10）was between 1.26～2.50μg·kg^–1,and the recovery rate was 81.8%～110.8%.The intra-day and inter-day precision（RSDs）was less than 8.8%.The results showed that this method is applied to the quantitative analysis of trace PAHs pollutants in soybean samples,with high sensitivity,good selectivity and reproducibility,and reliable results.（2）The post-modified synthesized NH₂-ZIF-8 was modified with acryloyl chloride to prepare vinyl ZIF-8,which was used as a comonomer,ethylene glycol dimethacrylate（EGDMA）was used as a crosslinking agent,methanol and dimethyl sulfoxide is a mixed porogen.ZIF-8 poly（EGDMA）copolymer monolithic column was prepared by thermally initiated polymerization.The physical morphology and chemical structure of the material were characterized by scanning electron microscopy,powder X-ray diffraction,fourier transform infrared spectroscopy,thermogravimetric analysis,and specific surface area determination,as well as the adsorption performance of the material.The results of adsorption experiments show that the copolymer monolith has good adsorption selectivity for 3 PAHs,PHE,FLT and PYR,with adsorption capacities of 138,115 and 130 mg·g^–1,respectively.Under the premise of ensuring the recovery rate of quantitative analysis,the copolymer monolithic column can be reused 50 times,indicating that the copolymer monolithic column has good adsorption reproducibility and service life.The copolymer monolithic column was applied to solid phase microextraction.After optimizing the sample solution volume,flow rate,salinity,and eluent acidity,volume and flow rate,the SPME-HPLC separation and analysis method for PHE,FLT and PYR in cereal samples was established.The linear range of this method for PHE and PYR was 0.06～400μg·kg^–1,the linear range for FLT was 0.10～400μg·kg^–1,the correlation coefficient（R²）was greater than 0.99,the detection limit（LODs,S/N=3）was 0.02～0.03μg·kg^–1,the limit of quantification（LOQs,S/N=10）was between0.06～0.10μg·kg^–1,and the recovery rate was 82.1%～114.9%.The intra-day and inter-day precision（RSDs）was less than 9.5%.Compared with the ZIF-8 polymer monolithic column,the preparation process of the ZIF-8 copolymer monolithic column is simple and has a larger specific surface area and adsorption capacity.The established quantitative analysis method has high sensitivity and good reproducibility,and is suitable for the separation and analysis of PAHs in cereal samples.