Optimization of a DI-SPME-GC-MS/MS method for multi-residue analysis of pesticides in waters

This paper discusses the optimization and validation of a complete and simple method for the simultaneous determination of 48 pesticides in water by combining direct immersion solid-phase micro-extraction (DI-SPME) and gas chromatography-ion trap tandem mass spectrometry (GC-ITMS/MS). For the extraction, the different SPME parameters were tested and optimized. As a result, the polyacrylate fiber (PA 85 mu m) was selected in direct immersion mode; the extraction temperature was set to 60 degrees C with an extraction time of 45 min and a stirring speed of 500 rpm; the thermal desorption time of the fiber in the injector port was fixed to 10 min at 275 degrees C. Concerning the analysis, MS/MS parameters were optimized and figures of merit were compared. Later, the method was validated and showed good linearity in the concentration ranging from 0.05 to 100 mu g L-1. The reproducibility of measurements expressed as the relative standard deviation (% RSD) was found to be satisfactory. Furthermore, the detection limits for all the compounds were between 0.001 and 0.458 mu g L-1, except for methomyl and hexachlorobenzene (1.09 and 0.99 mu g L-1 respectively). Finally, the proposed DI-SPME-GC-MS/MS method was tested successfully for water samples collected along the watershed of Abou Ali River (North Lebanon).