Abstract
A rapid method for simultaneous determination of both carbimazole and methimazole by third derivative spectrophotometry is presented. First derivative spectrophotometry is also applied for selective determination of carbimazole in the presence of methimazole. By measuring the absolute values of the first (for carbimazole) and third derivative curves for the mixture, the concentration of each component can be calculated directly without interference from the other.
The method was proved using prepared mixtures of the two drugs. The mean accuracies for the determination of carbimazole by first and third derivative spectrophotometry were found to be 100.02 +/- 0.29, 100.07 +/- 0.17, respectively and 99.97 +/- 0.09 for methimazole by third derivative spectrophotometry. The proposed procedures were successfully applied for the analysis of carbimazole in tablet form and its validity was further checked using the standard addition technique.