Targeted class analysis of β-lactam antibiotics by tandem mass spectrometry

Another promising application area for tandem mass spectrometry is targeted class analysis. Particularly favorable examples of this are analyses for penicillins and other β-lactams, important compound classes sought in complex mixtures. Electron ionization of these compounds produces a major fragment ion by lactam ring cleavage; collisionally activated dissociation of this ion yields spectra characteristic of the compound class. Four isomeric [C7H12NO2S]+ ions and two homologous ions illustrate these points. Their collisionally activated dissociation spectra, like the corresponding molecular electron ionization spectra, show fragmentations characteristic of the β-lactam ring size and of substituent type and position, but not of stereochemistry.