Trace determination of five organophosphorus pesticides by using QuEChERS coupled with dispersive liquid–liquid microextraction and stacking before micellar electrokinetic chromatography

Abstract

A procedure involving QuEChERS sample extraction combined with dispersive liquid–liquid microextraction (DLLME) and stacking as off-line and on-line preconcentration techniques followed by micellar electrokinetic chromatography (MEKC) has been developed for the determination of five organophosphorus pesticides (dimethoate, phosphamidon, paraoxon-methyl, paraoxon and fensulfothion). The important parameters that influence the stacking and DLLME efficiency were evaluated. The RSDs of the migration time ranged from 0.06% to 1.03% and the peak area ranged from 1.12% to 5.15% for the five analytes, indicating the good repeatability of the method. The method was extensively validated by evaluating the linearity (r² ≥ 0.9956), LODs (0.010–0.018 μg mL⁻¹) and recovery (78.75–118.15%). The QuEChERS–DLLME–stacking–MEKC method has been successfully applied to assay the five organophosphorus pesticides in Astragalus membranaceus. Under the optimized conditions, the proposed method provided a 90.0- to 167.3-fold enrichment of the five pesticides compared with the normal MEKC method, which offers an ideal solution for the determination of some trace pesticides in real samples with complex matrices.