Graphitized carbon black extraction cartridges for monitoring polar pesticides in water

Our previously reported procedure for analyzing pesticides in aqueous samples involving liquid-solid extraction by graphitzed carbon black (GCB) followed by liquid chromatography was appropriately modified for extending the analysis to very polar pesticides and pesticide metabolites. For this purpose, a 1-g GCB reversible extraction cartridge was adopted. Pesticide reextraction was performed by back-flushing the cartridge with a suitable eluant phase. The advantages of back-flush over forward flush desorption are illustrated. On extracting 2 L of drinking water spiked with the pesticides considered, the performance of the GCB cartridge was compared to that of a 1-g C18 bonded silica cartridge as well as to those of discontinuous and continous liquid-liquid extraction (LLE) techniques. The influence of the presence of humic substances in water on the quality of the analysis of the pesticides considered was assessed. The limits of quantification (5 times the limit of detection) of this method for the pesticides considered by analyzing municipal waters were below 0.1 mug/L, except for vamidothion and cymoxanil. Quantitative recoveries of even the most polar pesticides were obtained by submitting to the analysis volumes of ground and surface water samples no greater than 1 and 0.5 L, respectively.