Cleanup methods,pesticide column chromatography

The solvent extracts can be cleaned up by traditional column chromatography or by solid-phase extraction cartridges. This is a common cleanup method that is widely used in biological, clinical, and environmental sample preparation. More details are presented in Chapter 2. Some examples include the cleanup of pesticide residues and chlorinated hydrocarbons, the separation of nitrogen compounds from hydrocarbons, the separation of aromatic compounds from an aliphatic-aromatic mixture, and similar applications for use with fats, oils, and waxes. This approach provides efficient cleanup of steroids, esters, ketones, glycerides, alkaloids, and carbohydrates as well. Cations, anions, metals, and inorganic compounds are also candidates for this method [7],... 

Sometimes, the gas chromatographic retention times of two or more materials are so close that an identification is difficult, even if two different columns have been used. A thin layer chromatography separation (Chapter 22) then can be used, but this generally requires a lengthy cleanup and concentration because of the small (nanogram) samples involved. A much quicker method is the use of P-values. This method is based on the distribution of the pesticides between two immiscible phases. 

Eight carbamate pesticides were analyzed in bovine rumen. The method was based on extraction, partition, and an addititmal sweep condistillation step. This cleanup gave more re oducible results compared to cellulose-carbon column cleanup. The spots were visualized with either anisaldehyde or lV,2,6-trichloto-benzoquinoneimine after reversed-phase TLC (68). Carbamate and urea herbicides such as chlorpropham, metobromuron, and chlorbromuron were determined in medicinal plants by TLC. First they were hydrolyzed by alkali to 3-chloro-, 4-bromo-, and 3-chloro-4-bromoaniIines. These aniline derivatives were detected with 4-dimethylaminobenzaldehyde after TLC separation (Table 4) (69). Af-methyl carbamate pesticides can be separated by reversed-phase chromatography and analyzed by MS (70). 

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