Optimization of the HPLC [high performance liquid chromatography] method to determine oxadiazon (herbicide) residues in water, soil, and rice grain samples
2015
Bunquin, M.A. | Onoya, J. | Chauhan, B. | Opeña, J. | Beebout, S.J.
Weeds are the major limitations to direct-seeded rice systems. In order to achieve a sustainable weed control practice, it is important to combine appropriate herbicide mixtures with timing and rotation. The World Health Organization is estimating the risk of exposure from consuming food and drinking water containing pesticide residues, and assessing whether it is within the maximum residue limit. Oxadiazon is a pre-emergence herbicide that control grasses and broadleaf weeds and sedges in irrigated rice farming. The objective of this study is to perform validation and optimization of the high-performance liquid chromatography (HPLC) in measuring oxadiazon residues in water, soil, and grain samples collected from an oxadiazon-treated field. Inflow and outflow water samples collected 1-3 weeks after treatment were stored in a freezer and filtered prior to analysis. Soil samples collected at the same time with the water samples were air-dried and finely ground prior to extraction with acetonitrile. Grain samples were air dried at 11-14% moisture content and stored in a cool, dry place. Further cleanup using C18 solid-phase extraction while soil and grain extract were evaporated before injecting them into an HPLC system consisting of an Agilent 1230 Infinity Series Model, a C18 column, and a UV detector. Results from the method validation gave a Limit of Detection of 0.01 mg/L, and a Limit on Quantitation of 0.03 mg/L. The percent recoveries for the analysis of all samples are more than 80%. It was shown that some water samples coming from the inflow are contaminated with oxadiazon in soil samples, oxadiazon persisted after more than 20 days of application. Oxadiazon is also detected in grain samples, where the concentration is higher in the hulls.
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