DETERMINATION OF PHENOXY ACID HERBICIDES FROM AQUEOUS SAMPLES BY IMPROVED CLEANUP ON POLYMERIC PRE-COLUMNS AT HIGH PH

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 pr e-column at pH 2.8, a clean-up step at high pH and subsequent desorpti on 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 fav oured by a washing step with 0.1 mol l(-1) sodium hydroxide solution, As regards LC, gradient elution is applied using solvents with low buf fer and ion-pairing concentrations. The detection limits for the pheno xy acids (UV detection at 232 nm) are 5-20 ng l(-1) for tap water samp les, At the 0.1 mu g l(-1) spiking level, the RSD is 6% (n = 7) and th e recoveries are better than 83% for all analytes. The long-term repro ducibility typically has RSD values of 5% (n = 7), The method was succ essfully tested on water samples from various origins, and the results obtained with the present on-line SPE-LC-UV procedure mere found to c ompare well with those obtained with procedures involving SPE combined off-line with GC-MS or flow injection MS-MS.