Troubleshooting in the trace analysis of organochlorine pesticides in water samples

Summary As a consequence of the high toxicity of organochlorine pesticides their presence in water for human consumption is limited by legislation. To determine these compounds at trace levels, an extraction procedure and a highly sensitive analytical technique is necessary. In this work we have used laminar disks for the solid-phase extraction of 21 organochlorine pesticides from water. The analytical technique selected is gas chromatography with electron-capture detection. A solid-phase extraction procedure is proposed, and some problems has been encountered. Low recovery of some pesticides has been obtained, because of their adsorption by the walls of containers. To prevent 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 filters usually used to remove suspended particulate matter from water samples. Different kinds of filters have been tested, and the occurrence of the problem has been confirmed. The use of laminar disks in this work has overcome this problem.