Ion/surface collisions: an alternative to gas-phase collisional activation in mass spectrometry

In order to characterize an ion in mass spectrometry, be it the molecular ion or any of its fragments, it is often necessary to employ an extra stage of analysis, in addition to plotting its normal mass spectrum. In a typical procedure, the ion to be studied is selected by the first analyzer, it then undergoes an activation and fragmentation process, and, finally, the fragmentation products are separated by the second analyzer and registered at the detector. This technique has been named tandem mass spectrometry1 for obvious reasons: there are two mass analyzers and they work in tandem. Another way of denoting this method is by the acronym MS/MS, which was introduced as a parallel to the GC/MS notation.2 Indeed, the two techniques share thesamebasicprinciple: the first stage is theseparationofonespecies from the rest – it can be achieved by gas chromatography, in the case of a mixture of compounds, but it can also be effected by a mass analyzer, in the case of a mixture of ions. TheMS/MSsymbolismseems tobeprevailing latelydue to thedevelopmentofmass spectrometers which enable three, four or more stages of analysis; thus, the corresponding tech-