Moisture-sensitive metal–organic framework constructed from cobalt and 4-(4-pyridyl) benzoic acid for dispersive solid-phase extraction of polycyclic aromatic hydrocarbons in apple

A moisture-sensitive metal-organic framework Co II (pybz) 2 ·2DMF was synthesized and applied as the adsorbent of dispersive solid-phase extraction. The structure changed after water treatment due to the fact that two chelate carboxylate groups on the skeleton were transformed to monodentate because of the coordination of water molecules. The material showed good adsorption for fluorene, phenanthrene, fluoranthene, and pyrene in water because of the π–π conjugation and π-complexation effects. Coupled with high-performance liquid chromatography, a dispersive solid-phase extraction method of determining the content of fluorene, phenanthrene, fluoranthene, and pyrene in apple samples was established after optimizing the extraction conditions. Methanol containing 4% acetic acid was used as the effective eluent. The linearities were 0.5–1000 μg/kg for fluorene, phenanthrene and 5–1000 μg/kg for fluoranthene, pyrene. The limits of detection were 0.06–0.6 μg/kg, and the recoveries were 94.4–116.4%. The method has a high sensitivity for the determination of four polycyclic aromatic hydrocarbons in apple samples.