Single-drop microextraction for the analysis of organophosphorous insecticides in water

A new method used for the extraction of 10 organophosphorous insecticides from water samples coupling single-drop microextraction with gas chromatography–mass spectrometry is presented here. Parameters, such as organic solvent, exposure time, agitation, organic drop volume and salt concentration were controlled and optimised. Overall, extraction was achieved by suspending a 1.5 (mu)l toluene drop to the tip of a microsyringe immersed in a 5 ml donor aqueous solution containing 2.5% NaCl (w/v) and stirred at 800 rpm. The developed protocol was found to yield a linear calibration curve in the concentration range from 0.5 to 100 (mu)g1^-1 for all target analytes. Under selected ion monitoring mode, the limits of detection were found to be in the range between 0.010 and 0.073 (mu)g1^-1. The intra-day and inter-day repeatability of the method varied between 8.6 and 16, and 11 and 19%, respectively. The relative recoveries from several types of natural water samples were evaluated and the effect of dissolved organic matter (humic acids) was investigated. Finally, the performance of the proposed method was compared to that of solid-phase microextraction. Overall, singledrop microextraction proved to be a fast and simple tool for the preconcentration of organophosphorous insecticides from water samples.