Colorimetric Determination of Some Drugs Containing Phenolic Group Using 3-Methyl -2- Benzothiazolinon Hydra zone Hydrochloride (MBTH)

Abstract

A simple, rapid, sensitive and suitable method for analysis of A methyldopa(I), levodopa (II) andcarbidopa (III) either in pure from or in pharmaceutical formulations is described. The proposed method is based on an oxidative coupling reaction with 3-methyl-2-benzothiazolinon hydra zone hydrochloride (MBTH) in the presence of an oxidant (Ce+4 or Fe+3) to give colored species. The resulting colors are well developed within 5 minutes at 20 ± 5°C and
stable for at least 2 hours. The λmax were 517, 477 and 474 nm for I, II, both III and IV respectively. A linear correlation was found between the absorbance and the concentration. Beer's law was obeyed for concentration ranges from 1-7 mg/ml, 1- 11 mg/ml, 1-8 mg/ml and 2-24 mg/ml for I, II, III and IV, respectively. The molar absorptiveness and was calculated. The results of analysis of pure drugs by the proposed method are in good agreement with the official BP and USP methods. The results obtained showed recoveries of 99.80 ± 0.27, 100.40 ± 1.26, 99.89 ±0.21 and 99.96 ± 0.36 for I, II, III and IV, in order. The proposed method was successfully applied to determine the studied drugs in their pharmaceutical dosage forms.