RAPID METHOD FOR THE DETERMINATION OF 8 CHLOROPHENOXY ACID RESIDUES IN ENVIRONMENTAL WATER SAMPLES USING OFF-LINE SOLID-PHASE EXTRACTION AND ONLINE SELECTIVE PRECOLUMN SWITCHING

A rapid procedure for the determination of eight chlorophenoxy acid he rbicides in environmental water samples is described. The method invol ves two off-line solid-phase extraction (SPE) procedures prior to anal ysis by liquid chromatography with (pre)column switching and UV detect ion at 228 nm. SPE sample pretreatment consists in loading a 50-ml sam ple on a 100-mg C,8 cartridge followed by clean-up of the extract on a 100-mg silica cartridge. The extracts obtained by this procedure are analysed with coupled column liquid chromatography (LC) using a precol umn packed with internal surface reversed-phase material (5-mum GFF II ) and an analytical column packed with C18 material (3-mum Microspher) . The separation of the extracts from the SPE procedure takes less tha n 15 min, rendering an overall procedure with a throughput of 40 sampl es per day. The chlorophenoxy acids 2,4-D, MCPA, 2,4-DP, MCPP, 2,4,5-T , 2,4-DB, MCPB and 2,4,5-TP can be assayed in the various water sample s down to a level of 0.1 mug l-1. Drinking, ground and surface water s amples spiked at levels of 0.5 and 2.0 mug l-1 yielded average recover ies between 80 and 110% (n = 5 for each sample type and spiked level) with relative standard deviations between 1 and 10%. The calibration g raphs are linear over at least three orders of magnitude.