Simultaneous Determination of Five Benzimidazoles in Agricultural Foods by Core-Shell Magnetic Covalent Organic Framework Nanoparticle–Based Solid-Phase Extraction Coupled with High-Performance Liquid Chromatography

In this study, core-shell magnetic covalent organic framework nanoparticles (Fe3O4@COF) were prepared as solid-phase extraction (SPE) sorbents for simultaneous determination of five benzimidazole (BZD) residues in fruits and commercially available juices. Fe3O4@COF was prepared using the controllable in situ growth strategy and then fully characterized. This sensitive and selective analytical method was developed by combining the rapid magnetic SPE procedure and high-performance liquid chromatography (HPLC). The large surface area and suitable pore size of Fe3O4@COF facilitated the selective absorption of BZDs free from macromolecular interference. Several experimental parameters affecting the extraction efficiency were investigated, including adsorption isotherms, kinetics, pH and salt strength of sample solution, desorption eluents, and time. Furthermore, under the optimized conditions, the limit of detection and the limit of quantification were found to be less than 2.9 and 9.7 ng mL−1, respectively, along with good linearity at 0.01–0.2 μg mL−1 for all the five BZDs. When the proposed method was applied to fruits and juice samples, the recoveries ranged from 85.3 to 102.3%, with relative standard deviations always being < 8.6%. These results prove that the established method was fast, convenient, and feasible for the detection of BZDs in commercial food samples.