Determination of papaverine hydrochloride and dibazole in the combined presence by derivative spectrophotometry

UV-visible spectrophotometry is one of the methods widely used in pharmaceutical analysis. Difficulties that arise when analyzing systems containing components with overlapping absorption spectra can be overcome by differentiating the spectral data. In accordance with the principles of «green» analytical chemistry, the use of derivative spectrophotometry (DSP) in routine analysis is environmentally safer and more cost-effective than chromatography. The paper presents the results of assessing the possibility of determining papaverine hydrochloride (PPH) and dibazole (bendazole hydrochloride, BDH) without preliminary separation by the first-order DSP method at «zero-crossing». The zero-order absorption spectra of hydrochloric acid solutions of PPH and BDH and their first derivatives were studied, obtained using spectrophotometer software when scanning through 0.1, 0.2, 0.5, and 1.0 nm and differentiation (Δλ) from 1 to 80 nm. The influence of Δλ on the shape, d A /dλ values, position of extrema and «zero-crossing» with the wavelength axis of the derivative spectra has been established. The optimal differentiation parameters were determined for analysis of binary mixture: scanning the absorption spectrum through 0.2 nm, Δλ = 2 nm, scaling factor — 100. Analytical wavelengths at which the concentrations of components are directly proportional to the d A /dλ value were 247.2 and 212.6 nm for PPH and BDH respectively. The method was tested on model solutions; the accuracy of determination varied for BDH — from 97 to 105%, for PPH — from 96 to 103%. A simple and easily implemented method for determining PPH and BDH in one unit of dosage form has been developed, with the help of which «Papazol» tablets from two domestic manufacturers were analyzed. The relative standard deviation of the analysis results does not exceed 0.04. Checking the correctness of the methodology, carried out using the Vierordt method, confirmed the absence of systematic error.