Glutaraldehyde-functionalized urea-modified Fe₃O₄@TMU-16-NH₂ for magnetic solid-phase extraction of linuron and imidacloprid

A novel glutaraldehyde-functionalized urea-modified Fe₃O₄@TMU-16-NH₂ sorbent was synthesized and used for the magnetic solid-phase extraction (MSPE) of linuron and imidacloprid prior to high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Various parameters affecting the MSPE efficiency were systematically screened and optimized using Plackett–Burman design (PBD) and Box–Behnken design (BBD), respectively, to achieve optimal analytical performance. Under the optimized condition, the proposed method exhibited good linearity (R 2 > 0.9940) over the concentration range of 0.50–200.00 μg L −1 , with LODs and LOQs of 0.12–0.14 and 0.41–0.46 μg L −1 , for selected analytes, respectively. The method exhibited acceptable precision with relative standard deviations (%RSDs) ranging from 2.10 to 5.50%. The method achieved enrichment factors (EFs) of 128–135 and absolute recoveries (ARs) of 64.00–67.50%. The applicability of the developed method was successfully demonstrated through the determination of the target analytes in celery, soil, tomato, cucumber, and carrot samples. The obtained relative recoveries (RRs) were higher than 90%, confirming the reliability of the proposed method for the determination of linuron and imidacloprid in complicated matrices. The sorbent retained its extraction performance over nine consecutive reuse cycles, with no observable change in extraction performance. The greenness and practical applicability of the proposed method were also evaluated using the AGREEprep and BAGI metrics, yielding scores of 0.75 and 80, respectively. The proposed MSPE-HPLC-UV method enables the sensitive and reliable determination of linuron and imidacloprid at trace levels in complex matrices.