Determination of organochlorine pesticides in water samples by dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry.

A rapid and simple dispersive liquid-liquid microextraction (DLLME) has been developed to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples prior to analysis by gas chromatography-mass spectrometry (GC-MS). The studied variables were extraction solvent type and volume, disperser solvent type and volume, aqueous sample volume and temperature. The optimum experimental conditions of the proposed DLLME method were: a mixture of 10 microL tetrachloroethylene (extraction solvent) and 1 mL acetone (disperser solvent) exposed for 30 s to 10 mL of the aqueous sample at room temperature (20 degrees C). Centrifugation of cloudy solution was carried out at 2300 rpm for 3 min to allow phases separation. Finally, 2 microL of extractant was recovered and injected into the GC-MS instrument. Under the optimum conditions, the enrichment factors ranged between 46 and 316. The calculated calibration curves gave a high-level linearity for all target analytes with correlation coefficients ranging between 0.9967 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5% and 15% (n=8), and the detection limits were in the range of 1-25 ng L(-1). The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA methods 525.2 and 625. Analysis of spiked real water samples revealed that the matrix had no effect on extraction for river, surface and tap waters; however, urban wastewater sample shown a little effect for five out of eighteen analytes.