Facile Synthesis of Magnetic Covalent Organic Frameworks for Highly Efficient Extraction and Trace Determination of Ornidazole in Food Samples

Ornidazole (ONZ), a widely used nitroimidazole antibiotic, has raised significant environmental and health concerns due to its persistence and potential carcinogenicity. Existing detection methods often suffer from matrix interference and cumbersome procedures. In this study, a novel magnetic covalent organic framework (Fe 3 O 4 @TZ-DMTP) with a core-shell structure was synthesized via in situ hydrothermal growth of 2,4,6-tri(4-aminophenyl)-1,3,5-triazine (TZ) and 2,5-dimethoxy-terephthalaldehyde (DMTP) on magnetic nanoparticles. The composite exhibited high surface area, superparamagnetism and excellent adsorption capacity for ONZ through π-π interactions, hydrogen bonding, and hydrophobic effects. Coupled with HPLC-DAD, a robust magnetic solid-phase extraction (MSPE) method was developed, achieving a wide linear range (0.01-10 µg mL⁻¹) and low detection limit (0.003 µg mL⁻¹). The method demonstrated superior anti-interference capability and reusability (>90% recovery after 7 cycles). Successful application to tap water, lake water, aquaculture water, milk and honey samples confirmed its practicality with recoveries of 80.8-103.2% and RSDs < 13.8%. This work provides a sustainable and efficient strategy for monitoring nitroimidazole residues in complex matrices.