A method was developed for the quantitative determination of trace levels of the widely used herbicide sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} and its metabolites in an aqueous solution using reversed-phase high-performance liquid chromatography (HPLC). Optimum extraction of sethoxydim was with dichloromethane and was only 15% efficient at pH 3. The limit of detection by HPLC for sethoxydim was 5 ng on column and <5 ppb in soil. At least five different compounds were detected in the commercial formulation, in EPA reference standards, and in commercial sethoxydim standards. Sethoxydim undergoes a rapid decomposition in the presence of water to form more polar products, which accounts for the low extraction efficiency. Decomposition was greatest under alkaline conditions. Acid pH and soil inhibited decomposition and gave greater recoveries of parent compound. At least one breakdown product cochromatographed with a known sulfone derivative. The procedures are directly applicable to soils, environmental waters, and plant and animal tissues.
