The monocarboxylic and dicarboxylic acid metabolites of the herbicide Dacthal were quantitatively determined in groundwater samples by concentrating the analytes onto 13 mm diameter strong anion exchange (SAX) Empore disks. The carboxylic acid metabolites were then simultaneously eluted and derivatized to their ethyl esters by placing the 13 mm SAX disk in a 2 mL autosampler vial together with 140 /zL of ethyl iodide and 1 mL of acetonitrile and heating for 1 h at 100 °C. A recovery of 87.7 ± 1.0 (1.1% relative standard deviation, RSD) and 91.7 ± 0.9 (1.0% RSD) was obtained for the monocarboxylic and dicarboxylic acid metabolites from 100 mL samples of blank groundwater. Using a 100 mL sample, the detection and quantitation limits of the method are 0.02 and 0.06 /zg/L, respectively. The concentrations of the monocarboxylic acid metabolite ranged from less than the detection limit (0.02 /zg/L) to 1.04 /zg/L in a survey (4)

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Solid-phase extraction using strong anion exchange disks was evaluated as an alternative extraction method to conventional liquid-liquid extraction (LLE) for the quantitative analysis of the herbicide Dacthal (DCPA) and its mono-and dicarboxylic acid metabolites in ground water. The average recoveries of DCPA and its acid metabolites from deionized water were 93.7 & 2.6% and 85.6 f 2.5%, respectively. The detection limit of the SAX disk method is 0.05 pg/L for a 100 mL water sample. While no DCPA was detected in ground water from the Malheur River Basin in eastern Oregon, the total concentrations of the acid metabolites of DCPA in 100 mL samples of ground water ranged from less than the detection limit (0.05 to 158.2 pg/L and were in good agreement with those determined by means of conventional LLE.