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