[Tandem MS/MS combined with different ionization techniques in the study of steroid structures]

The various mass spectrometric ionisation techniques involve different ionisation energy. Their parallel application may provide complementary information for the structure. By the use of soft ionisation methods, especially when combined with tandem mass spectrometric techniques, stereospecific dissociation can also be detected, as the fragmentation processes of low energy differences result in significant abundance differences. The EI spectra of the stereoisomer compounds 1 and 2 are compared to their FAB-daughter ion spectra. This latter method leads to higher differences in the water elimination, indicating that the beta-hydroxi-isomer is more stable. ESI studies, using the "in-source CID" technique and also combined with MS/MS investigation have provided direct information about the position of substituents for the bis-quaternary salts of amino androstane derivatives, pipecuromium bromide [ARDUAN (3)] and its related compound 4. Due to the complementary information of the different ionisation methods used in mass spectrometry, the exact and detailed structural study requires the combined application of the various ionisation techniques together with MS/MS methods.