Use of liquid chromatography/tandem mass spectrometric (LC/MS(n)) molecular fingerprinting is systematically demonstrated as a very effective tool for rapid structural elucidation of pharmaceutical impurities through a case study in which three isomers of betamethasone sodium phosphate (BSP) were rapidly identified as degradants formed due to the D-homoannular ring expansion of the steroid core structure of BSP in the solid state. The rapid structural elucidation of these degradants was achieved by matching or closely matching the UV profiles, molecular weights, and more importantly the fragmentation patterns obtained from the LC/MS(n) (n = 1 to 3) analysis of their enzyme-catalyzed hydrolytic products, respectively, with those of a D-homoannular isomer of betamethasone available in our LC/MS(n) molecular fingerprint database. This strategy of using LC/MS(n) molecular fingerprinting to obtain high-confidence structures of unknown species is then validated by structure verification through one- (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) experiments.
Copyright 2009 John Wiley & Sons, Ltd.