Acetonitrile-driven interface force field reconstruction of HLB-SPME: insight into the pesticide adsorption mechanism based on energy lattice point models

Abstract

Solid-phase microextraction (SPME) is widely used in trace analysis, while traditional strategies mainly focus on coating modification, but the regulatory role of organic solvents in the interface force field remains unclear. In this study, acetonitrile was selected as the model solvent and 125 pesticides were selected as model analytes to investigate the effect of acetonitrile on the adsorption behavior of hydrophilic-lipophilic balance (HLB)-based SPME. Contrary to traditional understanding, adding a small amount of acetonitrile significantly enhances the pesticides' adsorption equilibrium constant (average 6.55-fold), with more pronounced effects on hydrophilic pesticides (log P < 1) than on hydrophobic pesticides (log P > 5), challenging the classic hydrophobic partitioning mechanism. Comparative analysis shows that the three-dimensional energy lattice point model outperforms the two-dimensional extended connectivity fingerprint model in predicting adsorption constants in acetonitrile-containing systems (training set R² = 0.86; test set R² = 0.53), effectively capturing steric and electrostatic characteristics. Molecular field analysis reveals that acetonitrile induces a force field conversion: the electrostatic field contribution increases from 1.5% to 21.4%, while the steric field contribution drops from 98.5% to 78.6%, shifting dominant adsorption forces from nonspecific van der Waals interactions to specific electrostatic interactions. Mechanistically, acetonitrile reshapes the solid–liquid interface via four synergistic effects: interfacial polarity regulation, microheterogeneous structure construction, interfacial enrichment, and diffusion pathway optimization. This study highlights the “solvent-mediated interface engineering” perspective for improving SPME performance, offering theoretical support for optimizing extraction conditions and designing selective materials.