Surfactant-less water emulsion based dispersive liquid-liquid microextraction for determination of organophosphorus pesticides in aqueous samples

A new sample preparation method, surfactant-less water emulsion based dispersive liquid-liquid microextraction coupled with gas chromatography-flame ionization detection, has been developed for the extraction, preconcentration and determination of some organophosphorus pesticides including diazinon, malathion, chlorpyrifos, profenofos, and phosalone from aqueous samples. In the present method an extraction solvent is dispersed into de-ionized water by repeated suction and injection of the extraction solvent and de-ionized water mixture using a syringe. This leads to formation of a water-based emulsion of the extraction solvent. Then this emulsion is rapidly injected into an aqueous sample solution containing the target analytes. Fine organic phase droplets are dispersed in all parts of the aqueous phase. Indeed de-ionized water acts as a disperser. After extraction, phase separation is performed by centrifugation and the enriched analytes in the sedimented phase are determined by the chromatographic system. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.65-4.2 and 1.9-13 ng mL(-1), respectively. Enrichment factors and extraction recoveries were in the ranges of 1280-1620 and 64-81%, respectively. Relative standard deviations for the extraction of 15 ng mL(-1) of each pesticide were less than 8.4% for intra-day (n = 6) and inter-day (n = 4) precisions. Finally some juice samples were successfully analyzed using the proposed method and two analytes, diazinon and phosalone, were determined in some of them at the ng mL(-1) level.