In the previous paper of this series, the mass spectrometric characteristics of methyl sterols were discussed. The present report deals with an extended study on 14 kinds of methyl oxo-steroids with saturated, Δ4-, Δ5- and Δ7-3-oxo steroidal skeltons.
Monomethyl oxo-steroids showed similar fragmentation pattern to the corresponding non-methylated oxo-steroids. On the other hand, fragmentation pattern of 4, 4-dimethyl oxo-steroids differed markedly from that of the non-methylated oxo-steroids. Several characteristic ions formed with rupture of ring AB were observed in the spectra of the former. It was suggested that the fragmentation process of molecule on 4, 4-dimethyl oxo-steroids was strongly controlled by 4, 4-dimethyl and 3-oxo groups.
