The identification of related substances in triamcinolone acetonide by means of high-performance liquid chromatography with diode array detector and mass spectrometry

A study of an HPLC method for the analysis of related substances in triamcinolone acetonide is described. Several systems of solvents and samples of different lots and preparative origins were examined and a rapid-scanning diode array UV detector (DAD) was particularly useful. With the proposed technique it was possible to identify 9 alpha-bromo desonide as a principal impurity, which was present in all examined samples of triamcinolone acetonide. This identification was rendered possible by the investigation of the second derivative of the UV spectra and by means of study of the mass spectrum. Furthermore, it was possible, primarily on the basis of the spectrophotometric data, to formulate reliable hypotheses on the possible identification of 9 beta, 11 beta-epoxide of the desonide which was present at very low levels and to exclude the presence of 11-deoxy-9(11)-unsaturated desonide. The presence of the above-mentioned related substances was explained considering the scheme of synthesis described in the literature. The spectrophotometric characteristics of the studied compounds and the limits of applicability of the present procedure are discussed.