Development of temperature-assisted solidification of floating organic droplet-based dispersive liquid–liquid microextraction performed during centrifugation for extraction of organochlorine pesticide residues in cocoa powder prior to GC-ECD

Abstract

A temperature-assisted solidification of floating organic droplet-dispersive liquid–liquid microextraction (DLLME) method has been developed for the extraction and preconcentration of some organochlorine pesticides (hexachlorocyclohexane, α-hexachlorocyclohexane, β-hexachlorocyclohexane, aldrin, and dichlobenil) from cocoa powder samples before their determination by gas chromatography–lectron capture detection (GC–ECD). In this method, first, 1 g of cacao powder was mixed with sodium chloride solution (5%, w/v) and the mixture vortexed. Then it was transferred into a water bath to adjust its temperature at 60 °C. After that, a mixture of 1-decanol (as extraction solvent) and ethanol (as a dispersive solvent) was quickly dispersed into the solution to form a cloudy solution. During centrifuging by a refrigerated centrifuge, the droplets of the extraction solvent containing the extracted analytes were solidified and collected on the top of the aqueous solution as a single drop. The solidified drop was withdrawn and after melting at room temperature an aliquot of it (1 µL) was injected into the separation system. Under optimized conditions, the proposed method provided high extraction recoveries (69–85%) and enrichment factors (69–85), low detection (0.027–0.052 ng g−1) and quantification (0.091–0.175 ng g−1) limits, wide linear ranges (0.091–500 ng g−1), and an acceptable repeatability (relative standard deviation ≤ 6.2%). Finally, several cocoa samples were analyzed, and aldrin and dichlobenil were found in one sample.