In-depth gas chromatography/tandem mass spectrometry fragmentation analysis of formestane and evaluation of mass spectral discrimination of isomeric 3-keto-4-ene hydroxy steroids.

With the help of stable isotope labelling, the structures of postulated diagnostic fragment ions for the different steroidal subclasses were elucidated. 18 O-labelling of the other compounds will be addressed in future studies to substantiate the obtained findings. To increase method sensitivity MS3 may be suitable in future bioanalytical applications requiring discrimination of the 2- and 4-hydroxy compounds.