Extraction and liquid-solid chromatography cleanup procedures for the direct analysis of four pyrethroid insecticides in crops by gas--liquid chromatography.

The extraction of four pyrethroid insecticides, fenpropanate (WL 41706, S-3206), permethrin (WL 43479, FMC-33297, PP 557, NRDC-143), cypermethrin (WL 43467, NRDC 149), and fenvalerate (WL 43775, S-5602) from carrots, tomatoes celery, and onions with acetone followed by extraction of the resulting acetone--water mixture with hexane, was investigated and found suitable for residue analysis. The elution of the four materials from two types of silica and alumina absorbents with mixtures of organic solvents of varying polarity was examined. The elution patterns and recoveries from silica gel, aluminum oxide, and water deactivated Florisil indicated potential utility in cleanup. Florisil was found to provide cleanup for asparagus, carrots, tomatoes, tobacco, and onions permitting analyses to less than 0.01 ppm for most of the insecticides by electron capture gas--liquid chromatography, at extract concentrations of 1 g/ml. The other adsorbents, singly or in combination, were found to provide the cleanup required for radishes and those cases involving other crops where Florisil cleanup was insufficient.