Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2007
Publication Date: 5/16/2007
Citation: Lin, C.H., Lerch, R.N., Garrett, H.E., Yong-Xi, L., George, M.F. 2007. An improved HPLC-MS/MS method for determination of isoxaflutole (Balance) and its metabolites in soils and forage plants. Journal of Agricultural and Food Chemistry. 55:3805-3815.
Interpretive Summary: Balance (isoxaflutole) is a relatively new corn herbicide introduced to the U.S. market in 1998. Balance is a very unstable compound without herbicidal activity, and it is rapidly converted in soil and water to a diketonitrile (DKN) metabolite, which is the actual herbicide compound. The DKN metabolite will itself degrade to a non-herbicidal benzoic acid (BA) metabolite. Balance was conditionally registered by the U.S. EPA because of concerns about surface and ground water contamination by DKN and BA. Since it is applied at low use rates (<0.1 lbs/acre), very sensitive analytical methods are required for detection of Balance and its metabolites in the environment. In this study, we developed methods for detection of Balance and its metabolites in soils and plants using high performance liquid chromatography (HPLC) with mass selective detection. For both soils and plants, the methods were sensitive to sub-part per billion levels. We then applied the methods to the measurement of Balance, DKN, and BA in soils and forage grasses to which Balance had been applied. In soils, Balance was not detected in any treatment and DKN was the predominant metabolite found. In forage grasses, significant levels of DKN and BA were present, but Balance was not detected. The developed methods provided the needed sensitivity to measure the Balance metabolites and to determine the fate of Balance and its metabolites in soils and forage grasses. These methods also represented significant improvements in detection sensitivity compared to previous analytical methods. Scientists, regulators, and industry will benefit from this work since appropriately sensitive methods are now available for measuring these compounds in the environment, which will facilitate an improved understanding of the environmental fate of Balance.
Technical Abstract: An analytical method using turbo-spray and heat-nebulizer high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed for the analysis of isoxaflutole (IXF) and its two metabolites, diketonitrile (DKN) and the benzoic acid metabolite (BA), at sub 'g/kg levels in soil and plant samples. The developed methods involved extraction of soils and plants with methanol, containing formic acid, followed by liquid-liquid extraction (for soils) and an additional solid-phase extraction step for plants. The average recoveries of the three compounds ranged from 82.2 to 112.8%. The limits of quantitation were validated at 0.06 'g/kg for soil and 0.3 'g/kg for plant samples. The limits of detection (LOD) for soil analysis were 0.01, 0.002, and 0.01 'g/kg for IXF, DKN and BA, respectively. Corresponding limits of detection for the plant analysis method were 0.05, 0.01, and 0.05 'g/kg. The developed method was then applied to measurement of IFX, DKN, and BA in a field experiment, involving field lysimeters with four forage treatments (orchardgrass, tall fescue, smooth bromegrass, and switchgrass). Forage plants and soils were sampled for analyses twenty-five days after IXF application to the soil. In soils, IXF was not detected in any treatment and DKN was the predominant metabolite found. In forage plants, significant levels of DKN and BA were present, but IXF was not detected in any forage plants. The much higher proportion of BA to DKN in plant tissues, as compared to soils, suggested that these forages were capable of detoxifying DKN. The developed methods provided sufficient LODs to determine the fate of IXF and its metabolites in soils and forage plants, and they also represented significant improvements in extraction recovery rates and detection sensitivity compared to previous analytical methods for these compounds.