Chlorinated acid herbicides in water by strong anion-exchange disk extraction and in-vial elution and derivatization

An analytical method for rapidly and quantitatively detecting chlorophenoxy acid herbicides in water is presented. Strong anion-exchange, 25-mm diameter solid-phase extraction disks are used to concentrate the chlorinated acid herbicides, including Dicamba, 2,4-D, Silver, 2,4,5-T, and Picloram, from surface water. The chlorinated acids are simultaneously eluted from the disk and derivatized to their methyl esters with an in-vial elution technique that requires heating the disk at 80 degrees C for 1 h in the presence of 1 mi acetonitrile and 200 mu l methyl iodide. Quantitative recovery (>95%) of all the acids was achieved from 500 ml samples with a single 25 mm diameter disk. The detection limits for 2,4-D and Dicamba are 0.36 mu g/l and 0.32 mu g/l, respectively, and 0.05 mu g/l for Silvex, 2,4,5-T, and Picloram. The quantitation limit of the method is 0.50 mu g/l for Dicamba, 0.70 mu g/l for 2,4-D, and 0.13 mu g/l for Silvex, 2,4,5-T, and Picloram. With this method a total of 10 ml of solvent is required to process a 500-ml sample, sample production capacity is 20 samples/day, and diazomethane is replaced by methyl iodide. The precision of the method, indicated by the relative standard deviation, for each herbicide ranged from 0.7 to 1.0% for concentrations between 3.28 and 7.03 mu g/l and 6 to 10% for concentrations from 0.10 to 0.49 mu g/l.