Electroanalytical determination of oxadiazon and characterization of its base-catalyzed ring-opening products

The electrochemical behavior of the hydrolysis products of oxadiazon was st udied by cyclic and square-wave voltammetry using a glassy carbon electrode . Maximum currents were obtained at pH 12.8 in an aqueous electrolyte solut ion containing 30% ethanol and the current did not decrease with time showi ng that there was little adsorption of the reaction products on the electro de surface. The hydrolysis products of oxadiazon were identified after isol ation and purification, as 1-trimethylacetyl-2-(2,4-dichloro-5-isopropoxyph enyl)-2-ethoxy-carbonylhydrazine (Oxa1) and 1-trimethylacetyl-2-(2.4-dichlo ro-5-isopropoxyphenyl) hydrazine (Oxa2) with redox potentials + 0.6V and -0 .1V (vs. Ag/AgCl), respectively. Based on the electrochemical behavior of 1 -trimethylacetyl-2-(2,4-dichloro-5-isopropoxyphenyl) hydrazine (Oxa2) a sim ple electroanalytical procedure was developed for the determination of oxad iazon in commercial products used in the: treatment of rice crops in Portug al that contain oxadiazon as the active ingredient. The detection limit was 1 x 10 (-4) M, the mean content and relative standard deviation obtained f or seven samples of two different commercial products by the electrochemica l method were 28.4 +/- 0.8 % (Ronstar) and 1.9 +/- 0.2 % (Ronstar GR), and the recoveries were 100.3 +/- 5.4 % and 101.1 +/- 5.3 %, respectively.