ADAPTATION AND APPLICATION OF A MULTI-RESIDUE METHOD FOR THE DETERMINATION OF A RANGE OF PESTICIDES, INCLUDING PHENOXY ACID HERBICIDES IN VEGETATION, BASED ON HIGH-RESOLUTION GEL-PERMEATION CHROMATOGRAPHIC CLEANUP AND GAS-CHROMATOGRAPHIC ANALYSIS WITH MASS-SELECTIVE DETECTION

A multi-residue method to determine pesticides in vegetation samples i s described. Blended samples were extracted with acetone and the pesti cides partitioned into dichloromethane prior to being cleaned-up using high-resolution gel permeation chromatography. Investigations were ma de into the effects of altering the pH of the aqueous phase during par titioning. Rapid and efficient methylation of the phenoxy acids presen t was achieved using trimethylsilyldiazomethane. The resultant solutio ns were then selectively and sensitively analysed by gas chromatograph y with mass-selective detection. The variation in results using matrix matched and non-matrix matched calibration standards was also explore d. The method has been applied to grass samples spiked with pesticides from the following groups, phenoxy acid, organophosphorus, triazine, organochlorine, phenyl urea, chloroacetanilide and pyrethroid. Recover ies around 80-100% and reproducibilities of 2-4% (n=4) were typically achieved at a spiking level similar to 140 mu g kg(-1).