Spectrophotometric determination of chlordiazepoxide and diazepam using orthogonal polynomials

Abstract

A direct spectrophotometric method for the determination of chlordiazepoxide and diazepam in the presence of their degradation products is presented. The method is based on the use of the combined polynomial method. Thus, the coefficient, p_w, of the combined polynomial, P_w, calculated over the wavelength ranges 230–318 nm at 8-nm intervals and 272–360 nm at 8-nm intervals for chlordiazepoxide and diazepam, respectively, in 0.1 N hyrochloric acid, is independent of the degradation products and is reproducible, with relative standard deviations of 0.46 and 0.19%, respectively. The mean recoveries for mixtures of each drug with the respective degradation products were 100.2 ± 1.2 and 100.2 ± 0.7%. When applied to commercial tablets, the results were in good agreement with the BP method. Plots of logarithm of concentration against time for a solution in 6 N hydrochloric acid gave straight lines with slopes of –0.0728 and –0.0250 d^–1 for chlordiazepoxide and diazepam, respectively. The proposed method is a stability-indicating method.