|Lerch, Robert - Bob|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2002
Publication Date: 9/12/2002
Citation: LIN, C.H., LERCH, R.N., THURMAN, E.M., GARRETT, H.E., GEORGE, M.F. DETERMINATION OF ISOXAFLUTOLE (BALANCE) AND ITS METABOLITES IN WATER USING SOLID PHASE EXTRACTION FOLLOWED BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY WITH UV OR MASS SPECTROMETRY. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. 2002. v. 50. p. 5816-5824. Interpretive Summary: Balance (isoxaflutole) belongs to a new family of herbicides referred to as isoxazoles. Balance represents a new strategy for weed control. The parent compound is a very unstable molecule without herbicidal activity. In order to be activated, Balance is converted to a more stable diketonitrile (DKN) metabolite, which is the actual herbicide compound. The DKN metabolite will itself degrade to a non-biologically active benzoic acid (BA) metabolite, which is quite stable and water soluble. The intended strategy of the manufacturer is that under field conditions Balance will convert to DKN in a series of pulses following rainfall, a so-called recharge mechanism that can provide residual weed control. Balance is intended to perform well at relatively low dosages (about 0.01-0.06 lbs./acre of active ingredient). The U.S. Environmental Protection Agency (EPA) gave conditional regulatory approval to Balance in 1998 because of concerns associated with surface and ground water contamination by the DKN and BA metabolites. The objective of this research was to develop methods for analyzing Balance, DKN, and BA in water samples using commonly available ultraviolet (UV) detectors as well as more sophisticated instrumentation that detects the compounds based on their mass. The method based on UV detection worked well for Balance and the DKN metabolite, but the BA metabolite was difficult to detect because of interfering compounds. The method based on mass detection was superior to UV detection since interfering compounds were minimized. The mass detection method is also more sensitive, providing detection down to 50 parts per trillion for all three compounds. These methods will primarily benefit researchers, regulators, and analytical laboratories by providing methods for studying the fate of Balance in the environment.
Technical Abstract: Balance (isoxaflutole) belongs to a new family of herbicides referred to as isoxazoles. Isoxaflutole (IXF) has a very short soil half-life (less than 24 hr) degrading to a biologically active diketonitrile (DKN) metabolite that is more polar and considerably more stable. Further degradation of the DKN metabolite produces a nonbiologically active benzoic acid (BA) metabolite. Analytical methods using solid phase extraction followed by high-performance liquid chromatography-UV (HPLC-UV) or high-performance liquid chromatography-mass spectrometry (HPLC-MS) were developed for the analysis of isoxaflutole and its metabolites in distilled deionized water and ground water samples. To successfully detect and quantify the BA metabolite by HPLC-UV from ground water samples, a sequential elution scheme was necessary. Using HPLC-UV, the mean recoveries from sequential elution of the parent and its two metabolites from fortified ground water samples ranged from 68.6 to 101.4%. For HPLC-MS, solid phase extraction of ground water samples was performed using a polystyrene divinylbenzene polymer resin. The mean HPLC-MS recoveries of the three compounds from ground water samples spiked at 0.05 to 2 ug/L ranged from 100.9 to 110.3%. The limits of quantitation for HPLC-UV are approximately 150 ng/L for IXF, 100 ng/L for DKN, and 250 ng/L for BA. The limit of quantitation by HPLC-MS is 50 ng/L for each compound. The methods developed in this work can be applied to determine the transport and fate of Balance in the environment.