In this paper, a dispersive liquid-liquid microextraction method with a new sequence of steps from the view of salt addition has been developed for the extraction and preconcentration of some organophosphorous pesticides from aqueous samples before analysis by gas chromatography with flame ionization detection. In this method, an appropriate mixture of extraction and disperser solvents is rapidly injected by a syringe into the aqueous sample. Then, sodium chloride is added into the solution to increase its ionic strength. The obtained results by the proposed method are compared with those of the conventional dispersive liquid-liquid microextraction in which the salt is added into the aqueous phase before dispersion of the extraction solvent. Some effective parameters on the method efficiency including type and volume of extraction and disperser solvents, type and percent of salt, etc. are investigated. Under the optimal conditions, limits of detection and quantification of the proposed method compared to conventional one were improved by a factor between 1.4-2.2 and 1.3-2.3, respectively. Extraction recoveries and enrichment factors of the proposed method with respect to conventional one enhanced from 43-60 to 72-99% and 1433-2000 to 2404-3285, respectively.
Keywords: Dispersive liquid-liquid microextraction; Gas chromatography; Organophosphorous pesticides; Salting out effect; Sample preparation.
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