Development of dispersive solid-liquid extraction method based on organic polymers followed by deep eutectic solvents elution; application in extraction of some pesticides from milk samples prior to their determination by HPLC-MS/MS

An effective extraction procedure based dispersive solid phase extraction was developed for the extraction of different pesticides (dimethoate, imidacloprid, pirimicarb, carbaryl, fenitrothion, hexythiazox, and phosalone) from milk samples. The analytes were determined by high performance liquid chromatography-tandem mass spectrometry. In this method, an organic polymer (polystyrene) was dissolved in a water-miscible organic solvent (tetrahydrofuran) and it was injected into the aqueous phase obtained from milk sample after deprotonation. By this action the sorbent (polymer) was precipitated and dispersed in the solution as tiny particles. By doing so, the pesticides were adsorbed onto the sorbent. After that, the sorbent was separated by centrifugation and the adsorbed analytes were eluted by tetrabutylammonium chloride: dichloroacetic acid deep eutectic solvent. After optimization, the method validation was followed according to Food and Drug Administration and International Research Council guidelines and the results showed that wide linear ranges (0.93–500 ng/mL) and low limits of detection (0.09–0.27 ng/mL) and quantification (0.31–0.93 ng/mL) were obtained. Extraction recoveries and extraction and enrichment factors were in the ranges of 81–94% and 162–188, respectively. Relative standard deviations were less than 9% for intra– (n = 6) and inter–day (n = 6) precisions at three concentration of 2, 5, and 25 ng mL⁻¹ of each analyte. The developed method was successfully applied to twenty cow milk samples for determination of the pesticides.