Analysis of betamethasone, dexamethasone and related compounds by liquid chromatography/electrospray mass spectrometry

A reversed‐phase high‐performance liquid chromatography/electrospray ionisation mass spectrometry (HPLC/ESI‐MS) method has been developed to conclusively differentiate the epimers betamethasone and dexamethasone and various esterification products (betamethasone and dexamethasone 21‐acetate, betamethasone and dexamethasone 21‐phosphate, betamethasone 17‐valerate, betamethasone 21‐valerate and betamethasone 17,21‐dipropionate) in counterfeit drugs. Good separation with baseline resolution of all epimers or isomers was obtained on a Zorbax Eclipse XDB or Luna C8 column, using a step gradient with mobile phases of 0.05 M ammonium acetate and acetonitrile. Betamethasones can also be distinguished by the relative abundance of their m/z 279 ion in the positive electrospray tandem mass spectra. The LC/MS or LC/MS/MS method developed was successfully applied to the analysis of drug product samples, i.e. creams and tablets. Copyright © 2004 John Wiley & Sons, Ltd.