Spectrophotometric Assessment of a Spectrally Overlapping Mixture of Cinchocaine Hydrochloride and Betamethasone Valerate in the Presence of Their Degradation Products

This work represents a contribution to the analytical spectrophotometric methods applied to resolve the spectral overlapping of cinchocaine hydrochloride (CIN) and betamethasone valerate (BMV), for the sake of their simultaneous determination in the presence of their hydrolytic degradation products and in the pharmaceutical formulation, with no need for preliminary separation. Conventionally assisted mathematical univariate techniques, including the use of the isoabsorptive point, dual wavelength, ratio subtraction, first derivative of the ratio spectra and ratio difference, are applied; these methods are able to determine the two drugs simultaneously in binary mixtures but not in the presence of their degradation products. For the determination of CIN, a direct measurement of its zero-order absorption spectra at 327.0 nm is performed, where BMV showed zero absorbance. Betamethasone valerate is determined by the developed univariate methods after resolving the CIN spectral overlapping. For the determination of both CIN and BMV in the presence of their degradation products, two multivariate calibration methods are proposed using principal component regression and partial least squares. The developed methods are validated as per the ICH guidelines and can be applied for routine quality control analysis.