Chiral separation of pesticides by coupled-column liquid chromatography. Application to the stereoselective degradation of fenvalerate in soil

Chiral separation of synthetic pesticides presenting more than one center of asymmetry was performed by multidimensional liquid chromatography.The method consisted of coupling two columns by means of a six-port valve: an achiral column was used for the separation of the pesticide diastereomers, that were,then, individually switched into the chiral column and resolved as the corresponding enantiomers. In order to obtain optimum resolution conditions for pesticides existing as four (fenvalerate, propiconazole, and triadimenol) and eight (cyfluthrin) optical isomers, a number of coupled-column systems constituted of an achiral (plain silica gel, ã-cyanopropyl(CNP)-, and ã-aminopropyl(AMP)-silanized silica gel) and a chiral [containing cellulose tris-(3,5-dimethylphenyl-carbamate),(R)(-)-N-(3,5-dinitrobenzoyl)-phenylglycine(DNBPG), and (S)-N-1-(á -naphthyl)ethylaminocarbonyl-(S)-ter-leucine, as the selectors] stationary phases were studied. Coupled-column liquid chromatography (CC-LC) proved to be a very effective strategy allowing the full resolution, with the exception of triadimenol, of all the investigated pesticides. The method was used for studying the stereoselective degradation of fenvalerate in soil under simulated laboratory conditions.