Magnetic chitosan-based solid-phase extraction for the determination of pesticides in water samples

In this study, a Fe₃O₄/chitosan magnetic composite was synthesized via a co-precipitation method and applied to magnetic solid-phase extraction (MSPE) for the determination of four pesticides-chlorbenzuron, bifenthrin, λ-cyhalothrin, and deltamethrin-in water samples. The prepared composite exhibited typical superparamagnetic behavior, with a saturation magnetization of 18.26 emu g^-1, enabling rapid solid-liquid separation within approximately 5 s under an external magnetic field. The extraction process was completed within 7 min. Compared with pristine chitosan, the specific surface area of the magnetic composite increased markedly from 0.8675 to 19.7250 m² g^-1. Abundant Fe-OH functional groups on the composite surface provided effective adsorption sites for the target pesticides. Good linearity was achieved for all analytes over the concentration range of 0.11-1000 μg L^-1 (R² ≥ 0.9960). After four consecutive adsorption-desorption cycles, the composite maintained satisfactory recovery performance, demonstrating good reusability. These results indicate that the Fe₃O₄/chitosan composite is an efficient and environmentally friendly adsorbent. The developed MSPE method offers a simple, rapid, and cost-effective approach for pesticide extraction and determination in water samples, with the added advantages of operational convenience and recyclability. Furthermore, adsorption mechanisms were systematically elucidated using FTIR, XPS, kinetic and isotherm analyses, revealing the involvement of non-covalent interactions (hydrogen bonding, Lewis acid-base interactions, electrostatic interactions, and hydrophobic effects), covalent coordination, and electron transfer. This study provides a valuable reference for the synthesis and application of related magnetic composites and offers mechanistic insights that support the development of green water treatment technologies.