Constructing magnetic covalent organic framework EB-COF@Fe3O4 for sensitive determination of five benzoylurea insecticides

•A new magnetic covalent organic framework (COF) was constructed.•The prepared magnetic COF exhibited excellent affinity to benzoylurea insecticides.•A sensitive method was developed for detection of five benzoylurea insecticides.•The magnetic COF could be used for selective extraction of benzoylurea insecticides. A magnetic covalent organic framework (COF) was constructed with ethidium bromide (EB) and 1,3,5-triformylphloroglucinol as building blocks. The prepared magnetic COF (named as EB-COF@Fe3O4) exhibited high adsorption ability for five benzoylurea insecticides (BUs). By combining EB-COF@Fe3O4 based magnetic solid-phase extraction with high performance liquid-phase chromatographic detection, a novel method was developed for determination of five BUs in water and food samples. Under the optimized conditions, a good linearity was obtained to be 0.03–100.0 ng mL−1 for water and juice, 0.9–500 ng g−1 for tomato. The detection limits of the method were 0.01–0.09 ng mL−1, 0.03–0.3 ng mL−1 and 0.3–2.0 ng g−1 for water, juice and tomato samples, respectively. Satisfactory method recoveries were achieved in the range of 80.0%-116.0% with the intra-day and inter-day relative standard deviations below 10%. Moreover, the EB-COF@Fe3O4 can be reused at least 25 times. Therefore, the established method is sensitive and robust for determining BUs in real samples.