Half protons or doubly charged protons? The history of metastable ions

Abstract

The history of metastable ions is intertwined with that of ions formed by collision-induced dissociation (CID), and frequently the genesis of the two ion types cannot be strictly separated. Originally, metastable ions were considered a curiosity or even a nuisance, being responsible for "humps" in the base line of the recorded mass spectra. In their heyday metastable ions were recognized as having importance for establishing fragmentation sequences and for distinguishing between isomeric ion structures. Today, in many respects the utility of metastable ions has been superseded by a systematic application of CID techniques; yet the evaluation of their shape is still of importance for questions of reaction energies and ion thermochemistry. (J Am Soc Mass Spectrom 2004, 15, 1261-1265

The triple quadrupole: Innovation, serendipity and persistence

“…Although these metastable peaks provided confirmation of a particular fragmentation path (m 1 + → m 2 + ), they were often considered more of a nuisance than an asset, and indeed some sector instruments included “metastable suppressors” to remove them from the mass spectrum (possible since they had less than full kinetic energy) [3] . But these metastable peaks also offered insight into the fundamentals of ion fragmentation and spawned the development of ion kinetic energy spectroscopy (IKES) and mass-analyzed ion kinetic energy spectroscopy (MIKES) to explore those insights [4] .…”

Suppression of unimolecular decay of laser desorbed peptide and protein ions by entrainment in rarefied supersonic gas jets under weak electric fields

“…Although MALDI was initially considered to be a soft ionization technique, it was later found that metastable decay (i.e., fragmentation of sample ions) does occur. [19][20][21][22][23][24][25][26][27][28][29] As discussed in detail by Karas,29 there are thought to be primarily three effects which contribute to fragmentation:…”