DETERMINATION OF METHIMAZOLE AND CARBIMAZOLE USING POLAROGRAPHY AND VOLTAMMETRY

Anodic waves of methimazole (I) (l-methylimidazole-2-thiol) and carbimazole (II) (1-ethoxycarbony1-3-methy1-2-thio-4-imidazoline) on mercury electrodes correspond to mercury salt formation. Both compounds form in the thiono form a soluble complex at pH< 6, compound (1) at higher pH-values a slightly soluble salt of the thiol form. Electrode processes involving the thiol form are complicated by adsorption. Oxidation at solid electrodes occurs only at potentials more than 0.5 V more positive. For compound (I) spectrophotometry indicated pKa - 12.0 2 0.2. taining 10% ethanol the determination of both compounds is possible between 4 x and 1 x M, by differential pulse polarography between 1 x 10 and 1 x M,,by differential pulse voltammetry at HMDE between 5 x loe7 and 6 x By d.c. polarography in 0.1 X H SO con-2 4-5 M. © 1990, Taylor & Francis Group, LLC. All rights reserved.