Determination of Phenoxy Acid Herbicides From Aqueous Samples by Improved Clean-up on Polymeric Pre-columns at High pH

Abstract

An improved procedure for the determination of phenoxy acid herbicides in environmental water samples is reported. The procedure consists in solid-phase extraction (SPE) of 60 ml water samples on a polymeric pre-column at pH 2.8, a clean-up step at high pH and subsequent desorption and ion-pair LC separation at pH 8.8. The main improvements are in the basic clean-up step and in the LC eluent composition. The release of compounds which are electrostatically bound to the precolumn is favoured by a washing step with 0.1 mol l ^{- 1} sodium hydroxide solution. As regards LC, gradient elution is applied using solvents with low buffer and ion-pairing concentrations. The detection limits for the phenoxy acids (UV detection at 232 nm) are 5–20 ng l ^{- 1} for tap water samples. At the 0.1 µg l ^{- 1} spiking level, the RSD is 6% (n = 7) and the recoveries are better than 83% for all analytes. The long-term reproducibility typically has RSD values of 5% (n = 7). The method was successfully tested on water samples from various origins, and the results obtained with the present on-line SPE–LC–UV procedure were found to compare well with those obtained with procedures involving SPE combined off-line with GC–MS or flow injection MS–MS.