Application of dispersive liquid–liquid microextraction for the analysis of organophosphorus pesticides in watermelon and cucumber

In this article, a new method for the determination of organophosphorus pesticides (OPPs) in cucumber and watermelon was developed by using dispersive liquid–liquid microextraction (DLLME) and gas chromatography–flame photometric detection (GC-FPD). Acetonitrile (MeCN) was used as extraction solvent for the extraction of OPPs from plant samples. When the extraction process was finished, the target analytes in the extraction solvent were rapidly transferred from the MeCN extract to another small volume of organic solvent, chlorobenzene, using DLLME. Recovery tests were performed for concentrations between 0.5 and 20 μg/kg; recoveries for each target analyte were in the range between 67 and 111%. The repeatability of the proposed method, expressed as relative standard deviation, varied between 2 and 9% (n = 3). Limits of detection of the method for watermelon and cucumber were found ranging from 0.010 to 0.190 μg/kg for all the target pesticides. Compared with the conventional sample preparation method, the proposed method has the advantage of being quick and easy to operate, and having high-enrichment factors and low consumption of organic solvent.