Abstract
Method for the analysis of paraquat and diquat with those oxidation products were studied by high performance liquid chromatography (HPLC) and thin-layer chromatography (TLC). Paraquat and diquat were easily oxidized by potassium ferricyanide in alkaline solution, and the former formed 1, 1'-dimethyl-4, 4'-bipyridyl-2, 2'-dione [I], the latter formed 6, 7-dihydrodipyrido [1, 2-a : 2', 1'-c] pyrazine-4, 9-dione [II]. Oxidative reaction of paraquat and diquat has been carried out in the stirred suspension of 1%-potassium ferricyanide in 9 N-sodium hydroxide at room temperature over 1 min. These oxidation products were determined by HPLC using a reversed phase column packed with Shim-pack CLC-ODS (6.0 mm i.d.×0.15 m) and an ionpairing reagent as a mobile phase with a fluorescence spectroscopic detector. The mobile phase consisted of 0.001 M sodium 1-octanesulfonate in 10% acetonitrile-10 mM phosphate buffer (pH 2.6). The calibration curves gave a good linearity in the range of 0.1-10μg/ml on paraquat and 0.3-10μg/ml on diquat. These oxidation products were separated on silica gel thin-layer chromatogram with a solvent system consisting of chloroform-acetone-methanol (8 : 1 : 1). Rf values of I and II were 0.47 and 0.64, respectively. Detection limits of paraquat and diquat were 20 ng and 10 ng, respectively.
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