Troubleshooting in the trace analysis of organochlorine pesticides in water samples

As a consequence of the high toxicity of organochlorine pesticides their pr esence in water for human consumption is limited by legislation. To determi ne these compounds at trace levels, an extraction procedure and a highly se nsitive analytical technique is necessary. In this work we have used lamina r disks for the solid-phase extraction of 21 organochlorine pesticides from water. The analytical technique selected is gas chromatography with elect ron-ca ptu re detection. A solid-phase extraction procedure is proposed, an d some problems has been encountered. Low recovery of some pesticides has b een obtained, because of their adsorption by the walls of containers. To pr event this adsorption, addition of 20% methanol before the sampling step is proposed. Adsorption of pesticides by the organic matter present in water samples was also observed. Pesticides can be adsorbed by the membrane filte rs usually used to remove suspended particulate matter from water samples. Different kinds of filters have been tested, and the occurrence of the prob lem has been confirmed. The use of laminar disks in this work has overcome this problem.