Quantitative Analysis of Diazepam Residues in Aquatic Products Using Magnetic Solid-Phase Extraction Combined with Ultra-High-Performance Liquid Chromatography–Tandem Mass Spectrometry

A method combining magnetic solid-phase extraction (MSPE) with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the determination of diazepam residues in aquatic products. A novel magnetic nanoparticle material, Fe₃O₄@SiO₂@DVB-NVP, was synthesized and applied as an adsorbent for sample cleanup. The sample preparation procedure involved extraction with 1% ammonia-acetonitrile, followed by purification using the MSPE technique to efficiently remove matrix interferents. Chromatographic separation was achieved on an ACQUITY UPLC BEH C₁₈ column with a gradient elution program using a mobile phase composed of 0.1% formic acid-2 mM ammonium acetate solution and methanol. Detection was performed under multiple-reaction monitoring (MRM) mode with positive electrospray ionization (ESI⁺). Quantification was carried out using the external standard method. The synthesized magnetic material was characterized using SEM, TEM, FTIR, XRD, BET, and VSM, confirming its mesoporous structure, strong adsorption capacity, and excellent magnetic responsiveness. The method demonstrated good linearity over the concentration range of 0.25-50 μg/L (<i>r</i>² = 0.997). The limits of detection and quantification were 0.20 μg/kg and 0.50 μg/kg, respectively. Average recoveries from spiked blank matrices at three levels (0.5, 2.5, and 5.0 μg/kg) ranged from 89.3% to 119.7%, with relative standard deviations (RSDs) between 0.8% and 10.2%. The proposed method is highly selective, exhibits minimal matrix interference, and provides reliable quantitative performance, making it suitable for the qualitative and quantitative analysis of diazepam residues in aquatic products.