Origin and Uses of Metastable Ions

Example of a mass spectrum showing the peaks (or lines) corresponding to ions measured at various m/z values by the spectrometer the heights of the peaks relate to the abundance of the ions. 

The first ionizatidn step in the source converts neutral molecules (M) into ions (M+). After a short time in the source, some molecular ions have fragmented to give smaller ions, F/, Fj, . .., F/, along one or more reactions pathways. An ion (F, ) formed in the source and then analyzed will have an m/z = x the same ion (F,+) formed outside the source will have an apparent m/z = y, where y x. 

Perhaps it is worth emphasizing that the actual metastable ions are those that decompose, and the so-called metastable ions that are recorded are actually the products of decomposition, not the metastable ions themselves. It is more accurate to describe the recorded metastable ions as ions resulting from decomposition of metastable ions. The apparent m/z value of a metastable ion provides the link between an ion that fragments (the parent or precursor ion) and the ion that is formed by the fragmentation (the daughter or product ion). 

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The controversy around the two possible origins of the BH ion (from direct pyrolysis or from the nucleoside-like ion) necessitated studies using linked scan techniques and metastable-ion mapping." From those results it is clear that the BH ions, as well as methylfuran particles, are formed directly by the pyrolitic process. 

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