Direct analysis of fenvalerate isomers by liquid chromatography. Application to formulation and residue analysis of fenvalerate

Summary The separation of the optical isomers of fenvalerate cyano(3-phenoxyphenyl)methyl 2-(4-chlorophenyl)-3-methylbutyrate] has been carried out by high-performance liquid chromatography (HPLC) on a chiral column with (R)-N-3,5-dinitrobenzoyl-phenyl-glycine (DNBPG) covalently bonded on aminopropyl silica and eluted with mixtures of methanol, 2-propanol, and hexane. The system was applied to the analysis of Pydrin^®, an emulsifiable concentrate formulation of fenvalerate, and to the residue analysis of fenvalerate in milk samples. For the analysis of Pydrin^® the only requirement was the proper dilution of Pydrin^® with hexane. For the analysis of residues in milk, fenvalerate was extracted with hexane after precipitating the milk proteins with acetonitrile and removing the precipitate by filtration; the hexane extract was concentrated to small volume and filtered before being analyzed by HPLC.