Magnetic solid phase extraction coupled with high-performance liquid chromatography-diode array detection based on assembled magnetic covalent organic frameworks for selective extraction and detection of microcystins in aquatic foods

It is crucially important to develop simple, selective, and rapid extraction pretreatments and analytical methods to detect microcystins (MCs) in food samples with complex matrices. In this study, a magnetic self-assembled covalent organic framework (COF) adsorbent was synthesized via a facile approach by using a one-pot reaction of 1,6-bis(4-formylphenyl)-3,8-bis(4-aminophenyl)pyrene (BFBAPy) as precursors to assemble amino-functionalized magnetic Fe3O4-NH2 nanoparticles (Fe3O4@Py-COF, simplified as mCOF). The superparamagnetic mCOF is found to exhibit a high specific surface area, abundant nanopores and good stability. In particular, adsorption experiments demonstrate that mCOF exhibits a good adsorption capability, efficiency and some specificity to MCs. The mCOF was applied for magnetic solid phase extraction (MSPE) of two kinds of MCs (MC-LR and MC-RR) from aquatic samples followed by high-performance liquid chromatography-diode array detection (HPLC-DAD). Under the optimized conditions, good linearity is obtained in the range of 10-1000 µg/kg (R2≥0.9989), the limits of detection are 3.0-4.5 µg/kg, and the relative standard deviations (RSDs) are lower than 4.9% (n=5). The extraction recoveries are also satisfactory (84.2%-105%). These results demonstrate that the developed method can be used as a good alternative method for the selective determination of MCs in complex aquatic foods.