Development of a magnetic core–shell adsorbent-based microextraction method for the determination of pesticide residues in edible vegetables

Abstract

For the first time, a new magnetic core-shell adsorbent (synthesized from Fe₃O₄, mercaptoacetic acid, and hexamethylene diamine) was introduced for the effective extraction of pesticide residues from agricultural products, including cucumber, tomato, and zucchini. The structural and magnetic characteristics of the synthesized adsorbent were fully confirmed through a series of instrumental techniques such as Fourier transform infrared spectrometry, scanning electron microscopy, Brunauer-Emmett-Teller, thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray, vibrating sample magnetometer, and zeta-potential analysis. The combination of dispersive micro solid phase extraction with dispersive liquid–liquid microextraction enabled a highly efficient two-step sample preparation protocol with minimal solvent consumption and rapid operation. Due to the magnetic nature of the adsorbent, phase separation was rapidly achieved using an external magnet, eliminating the need for repeated centrifugation and significantly reducing extraction time. The optimized procedure utilized only 3 mg of the sorbent and μL volumes of environmentally benign organic solvents, making the method green and cost-effective. Under the optimized conditions, the method achieved excellent analytical performance, including low detection limits (0.31–2.65 µg L⁻¹), wide linear ranges, good repeatability (relative standard deviations of 1.1–6.3%), high enrichment factors (225–480), and acceptable extraction recoveries (45–96%). The method was successfully applied to real agricultural matrices, and relative recoveries within the 80–120% range confirmed the absence of significant matrix effects. Altogether, this study highlighted a powerful and innovative analytical platform that offered high sensitivity, selectivity, and operational simplicity for the determination of pesticide residues in complex food samples.