Magnetic extraction of highly polar pesticides: Method optimization and mechanism

Monitoring pesticide exposure in human serum is essential for assessing internal exposure levels. In this study, we tested the hypothesis that carboxyl-functionalization of magnetic nanoparticles (Fe₃O₄@SiO₂-COOH NPs) significantly enhances the selective enrichment of polar pesticides via specific hydrogen-bonding and electrostatic interactions. To test this, we developed a magnetic dispersive solid-phase extraction method coupled with ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. The nanoparticles (14-15 nm, 28 emu/g) achieved 70.1-104.3% recoveries (RSDs 0.1-8.4%). The method exhibited excellent linearity (0.01-10 ng/mL) and low LODs (0.01-0.08 ng/mL), with matrix effects within -17.2% to +18.7%. Molecular modeling supported our hypothesis, identifying electrostatic attraction, van der Waals forces, hydrophobic interactions, and hydrogen bonding as primary binding mechanisms, and the binding energy was positively correlated with recoveries. Overall, this hypothesis-driven approach offers a potential biomonitoring method for the sensitive and accurate determination of polar pesticides in human serum, thereby facilitating more effective clinical and occupational exposure assessments.