Adduct formation of steroids in APCl and its relation to structure identification

Adduct ion formation is a frequently observed phenomenon in mass spectra originating from atmospheric pressure chemical ionisation processes. In this study the relation between the relative intensities of the deprotonated molecule and the acetate adduct ion and the chemical structure of some 22 corticosteroids was investigated. The ratio between the ion intensities of both ions changes upon the presence and the position of the hydroxy group in the steroid molecule. That is compounds without any hydroxy have a low tendency towards acetate adduct ion formation whereas its position influences the deprotonation of the molecule. From the data of this limited study it can be concluded that knowledge on the mechanism of adduct ion formation will be of help for structure identification studies.