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 clean-up and gas chromatographic analysis with mass-selective detection

A multi-residue method to determine pesticides in vegetation samples is described. Blended samples were extracted with acetone and the pesticides partitioned into dichloromethane prior to being cleaned-up using high-resolution gel permeation chromatography. Investigations were made into the effects of altering the pH of the aqueous phase during partitioning. Rapid and efficient methylation of the phenoxy acids present was achieved using trimethylsilyldiazomethane. The resultant solutions were then selectively and sensitively analysed by gas chromatography with mass-selective detection. The variation in results using matrix matched and non-matrix matched calibration standards was also explored. 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. Recoveries around 80-100% and reproducibilities of 2-4% (n=4) were typically achieved at a spiking level similar to 140 mu g kg(-1).