Synthesis Of Magnetic Covalent Organic Framework Materials Modified By Functional Groups And Their Applications In Sample Pretreatment

Covalent organic framework polymer,as a new type of porous material,has the characteristics of large specific surface area,high porosity and high stability,as well as predictability and diversity of structure.The magnetic material formed by the combination of covalent organic framework polymer and magnetic nanoparticles is paramagnetic nano-Fe₃O₄,which can be used to separate and enrich organic residues harmful to human health in food.A variety of complex components in food samples will interfere with the determination of low concentration residues,so it is necessary to carry out sample pretreatment to eliminate the interfering substances and enrich the analytes to be determined.Magnetic solid phase extraction(MSPE)is a simple sample pretreatment technology,which can disperse the synthesized magnetic materials directly into the sample solution,make the extraction materials fully contact with the target analyte,improve the extraction efficiency,and use the external magnetic field to quickly recover the extraction materials and simplify the extraction process.In this paper,a novel magnetic covalent organic framework material was used as adsorbent to determine different kinds of organic residues in food samples by high performance liquid chromatography.1.The classification,advantages and applications of porous materials were briefly introduced.The types and applications of composite materials formed by covalent organic framework materials and carbon materials,silica,metal organic framework materials and metal oxides were introduced.The synthesis methods of magnetic covalent organic framework materials and their applications in sample pretreatment as magnetic solid phase extraction adsorbents were mainly introduced.2.The magnetic covalent organic framework material COF(Tp Pa–NO₂)/Fe₃O₄ was synthesized by solvothermal method with 2,4,6-triformylphenylpyrogallol(Tp)and2-nitro-1,4-phenylenediamine(Pa-NO₂)as structural monomers.It was used as magnetic extractant to separate and enrich fluoroquinolones in milk samples,and analyzed and detected by HPLC-UV detector.Under the optimal extraction conditions,the adsorption equilibrium can be established in 4 min,the reusability of the adsorbent can reach 6 times,the linear range was 0.5–200?g/L,the detection limit was 0.25–0.54?g/L,and the quantitation limit was0.86–1.7?g/L.The recoveries were 81.4%–90.3%and the relative standard deviation was less than 6.3%.3.2,4,6-triformylpyrogallol(Tp)and 2-chloro-1,4-phenylenediamine(Pa-Cl)were selected as structural monomers,and Fe₃O₄ was added at the same time to prepare magnetic composite COF(Tp Pa–Cl)/Fe₃O₄ by simple room temperature stirring method.The composite nanomaterials were characterized and used for the separation and enrichment of two alkaloids,tibain and papaverine,in hot pot substrate.The results showed that the linear range was 0.01–200?g/L(correlation coefficient>0.9991),the detection limits were 0.1 and0.01?g/L,10.0 and 5.0?g/L,the recovery rate was between 81.6%–94.7%,and the relative standard deviation was less than 4.9%.4.The synthesized COF(Tp Pa–NO₂)/Fe₃O₄ was reduced to magnetic covalent organic framework material COF(Tp Pa–NH₂)/Fe₃O₄ by stannous chloride.A method for the analysis of three food pigments in carbonated beverages was established.The extraction conditions were studied systematically.The linear range was 3–500?g/L(correlation coefficient>0.9986),and the detection limit was 2.3–4.5?g/L,the limits of quantification were 8–15?g/L,the recovery rate was between 87.5%–96.9%,and the relative standard deviation was less than 4.6%.