A core-shell structured magnetic sulfonated covalent organic framework for the extraction of benzoylureas...

Three magnetic covalent organic frameworks (named M-TpPa-SO₃Na, M-TpPa-SO₃H and M-TpPa) were prepared by the solvothermal synthesis method with 1,3,5-trimethylphenol (TP) and either 2-sulfo-1,4-phenylenediamine (Pa-SO₃H) or p-phenylenediamine (Pa) as monomers. Among them, the M-TpPa-SO₃Na possessed relatively high hydrophilicity, good magnetic responsiveness, and high affinity for the benzoylureas (BUs) insecticides. It was then explored as the magnetic solid-phase extraction adsorbent for the extraction of six BUs (diflubenzuron, triflumuron, hexaflumuron, teflubenzuron, flufenoxuron and chlorfluazuron) from water, pear juice and honey samples prior to high-performance liquid chromatography with ultraviolet detection. Under the optimized experimental conditions, a good linearity was achieved within the concentration range of 0.27-40.0 ng mL^-1 for water sample, 0.47-30.0 ng mL^-1 for pear juice sample, and 2.70-200.0 ng g^-1 for honey sample. The limits of detection for the analytes were 0.08-0.11 ng mL^-1 for water sample, 0.14-0.19 ng mL^-1 for pear juice sample and 0.80-1.00 ng g^-1 for honey sample. The method recoveries for spiked samples were in the range of 85.0%-111.0% with the relative standard deviations less than 8.8%. The developed method was successfully used for the determination of the BUs in water, pear juice and honey samples.