Dacthal (DCPA) is a pre-emergence herbicide to control grass and common weeds without harming various flowers, fruits, vegetables, turf and cotton. DCPA degrades to tetrachloroterephthalic acid (TPA) and monomethyl tetrachloroterephthalic acid (MTP) by photo and biodegradation. The current EPA methods do not measure concentrations of the individual analytes, but a combined concentration of the degradants. This method determines the individual concentrations of DCPA, TPA and MTP, DCPA and its degradants, TPA and MTP were simultaneously extracted from 40 g of acidified groundwater using a 200 mg HLB extraction cartridge. The column was rinsed with 0.18 M H2SO4 and the analytes were eluted with diethylether (Et2O). The eluant was then treated with diazoethane in Et2O and the extract was evaporated to dryness. The extract was reconstituted with 0.1 mL of acetone, followed by 0.9 mL of isooctane. The extract was analyzed by a gas chromatograph (GC) equipped with a mass selective detector (MSD). The mean %recovery and its standard deviation for DCPA, MTP and TPA was determined to be 70.9 ± 4.5, 94.1 ± 6.9 and 76.2 ± 9.2, respectively. The MDL for DCPA, MTP and TPA was determined to be 6.3, 15.5 and 31.3 ppt (part per trillion), respectively. Reporting limit (RL) for this method is 50 ppt for each analyte. This method is currently being used to monitor well water throughout California farmland.

Simultaneous determination of dacthal and its degradants in ground water

ACS Fall 2020 Virtual Meeting

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