Facile preparation of core-shell magnetic organic covalent framework via self-polymerization of two-in-one strategy as a magnetic solid-phase extraction adsorbent for determination of Rhodamine B in food samples

The monomer of two-in-one molecular design strategy (i.e., A2B2 type monomer) 1,6-bis(4-formylphenyl)-3,8-bis((4-aminophenyl) ethynyl)) pyrene (BFBAEPy) was self-polymerized and coated on the modified Fe3O4 surface to synthesize a magnetic covalent organic framework (Fe3O4@COF) nanocomposite with a core-shell structure. Before high-performance liquid chromatography with ultraviolet detection (HPLC-UV) determination, Fe3O4@COF was used as a magnetic solid-phase extraction (MSPE) adsorbent to enrich Rhodamine B (RhB) illegally added to Chili powder and Chinese prickly ash. It had a large specific surface area and suitable pore size, which promoted the efficient adsorption of RhB dye and eliminated the interference of the matrix. Several key parameters affecting the extraction recovery rate were investigated, including adsorption capacity, adsorption time, pH, ionic strength, elution solvent, elution volume and elution time. Under the best optimized conditions, within the linear detection range of 0.05-5 µg/mL for RhB with the limit of detection (LOD) was 0.0038 µg/mL, excellent linearity (correlation coefficient R2=0.9997), and good repeatability (relative standard deviations RSD%< 3.8%), satisfactory extraction recovery rate (91.7%-97.5%). Therefore, the application of the established method to the detection of RhB in food samples has bright prospects.