Determination of organochlorine pesticides in complex matrices by single-drop microextraction coupled to gas chromatography-mass spectrometry.

A rapid and simple single-drop microextraction method (SDME) has been used to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples with a complex matrix. Exposing two microlitre toluene drop to an aqueous sample contaminated with OCPs proved an excellent preconcentration method prior to analysis by gas chromatography-mass spectrometry (GC-MS). A Plackett-Burman design was used for screening and a central composite design for optimizing the significant variables in order to evaluate several possibly influential and/or interacting factors. The studied variables were drop volume, aqueous sample volume, agitation speed, ionic strength and extraction time. The optimum experimental conditions of the proposed SDME method were: 2 microL toluene microdrop exposed for 37 min to 10 mL of the aqueous sample containing 0% w/v NaCl and stirred at 380 rpm. The calculated calibration curves gave high-level linearity for all target analytes with correlation coefficients ranging between 0.9991 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5.9 and 9.9% (n=8). The detection limits were in the range of 0.022-0.101 microg L(-1) using GC-MS with selective ion monitoring. The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA Method 625. Analysis of spiked effluent wastewater samples revealed that the matrix had no effect on extraction for eleven of the analytes but exerted notable effect for the other analytes.