Tandem mass spectrometry: A primer

Tandem mass spectrometry (MS/MS) employs two stages of mass analysis in order to examine selectively the fragmentation of particular ions in a mixture of ions. The various types of instruments which can be used to perform this experiment are described, including those based on separation of the mass-analysis events in time and those based on measurements in physically separate analysers. The several MS/MS scan types-product scans, precursor scans and neutral loss scans-are presented and examples of their applications are provided. These include the characterization of individual compounds and the recognition of groups of compounds with specified functional groups. Applications are shown to the determination of compounds present in complex mixtures. The improvement in signal-to-noise ratio achieved by MS/MS when compounds are ionized by methods which produce high chemical noise is illustrated for choline derivatives. Fundamental aspects of collisional activation in the low and high collision energy range are reviewed.