Methylene chloride pesticides from aqueous samples

In most environmental laboratories the classical liquid-liquid extraction using the separatory funnel is still the most used technique to extract semivolatile organic compounds, pesticides, and PCBs from aqueous samples. Methylene chloride (MeCl), although a potential health hazard, is one of the most commonly used solvents. Several physical properties make it advantageous to use. These properties are listed in Table 15.5. 

Column chromatography has been widely used for the cleanup of samples, either individually or after preliminary purification by solvent partitioning. An example of the latter is the quantitative TLC determination of the fungicides captan, folpet, and captafol in lettuce and apples (79). Samples were extracted by blending with acetone and the extracts were filtered, pesticides were partitioned from the aqueous filtrate with petroleum ether-methylene chloride (1 1), the organic layer was concentrated and diluted with acetone and petroleum ether, and the solution was chromatographed on an activated Florisil column with elution by 200 ml of 15% ethyl ether in petroleum ether followed by 200 ml of 50% ethyl ether in petroleum ether. The eluates were concentrated and aliquots spotted for TLC analysis. 

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