IN-VIAL DERIVATIZATION AND EMPORE DISK ELUTION FOR THE QUANTITATIVE-DETERMINATION OF THE CARBOXYLIC-ACID METABOLITES OF DACTHAL IN GROUNDWATER

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 mt autosampler vial together with 140 mu L of ethyl iodide and 1 mL of acetonitrile and heating for 1 h at 100 degrees 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 mu g/L, respectively. The concentrations of the monocarboxylic acid metabolite ranged from less than the detection limit (0.02 mu g/L) to 1.04 mu g/L in a survey of groundwater wells from eastern Oregon while the concentration of the dicarboxylic acid metabolite ranged from 0.60 to 180.70 mu g/L.