Facile synthesis of a core-shell structured magnetic covalent organic framework for enrichment of organophosphorus pesticides in fruits

A facile strategy was developed for the fabrication of a magnetic covalent organic framework (COF) via grafting of the monomers, 2,5-dihydroxyterephthalaldehyde (Dt) and 1,3,5-tris(4-aminophenyl) benzene (Tb) onto surface-modified Fe3O4 nanoparticles. The magnetic COF, named as magnetic COF-DtTb, was readily fabricated without high temperature or harsh reaction conditions. The synthesized magnetic COF-DtTb nanoparticles were fully characterized, presenting a regular core-shell spherical structure, large specific surface area, superparamagnetism, and good thermal stability. Their potential as an enrichment adsorbent was investigated to establish an efficient magnetic solid-phase extraction method for the determination of organophosphorus pesticide residues in fruits. Systematic method validation revealed good linearity in the concentration range of 1-200 μg L-1 (correlation coefficient >0.9957). The method limits of detection were in the range of 0.002-0.063 μg kg-1, the method limit of quantification was 1.00 μg kg-1 and recoveries ranged from 72.8% to 111% with RSDs lower than 12.3%. The results indicated that magnetic COF-DtTb possesses superior trace enrichment properties for organophosphorus pesticides in fruits.