A rule to account for mass shifts of even-electron fragment ions in fast-atom bombardment mass spectrometry

Abstract

A rule to account for mass shifts of even-electron fragment ions in fast-atom bombardment mass spectrometry a Hisao Nakata b 147-24, Arimatsu-ura, Narumi-cho, Midori-ku, Nagoya, 458-0824, Japan A rule is proposed for prediction of correct mass numbers of fragment ions in fast-atom bombardment (FAB) ionization mass spectrometry. The term "mass shift" in the rule is defined as the increment or diminution for the mass of an observed peak against the mass calculated from the corresponding part of the structural formula of a sample molecule. For positively-charged fragment ions, the mass shift is either 0, +1, +2 or even +3, according to the nature of the cleaved bond, and 0,-1 or-2 for negatively-charged fragment ions. The rule is based on the recognition that, with a few exceptions, fragment ions formed under FAB ionization are even-electron species and should have a stable structure which includes either (a) charged carbon atoms stabilized by conjugation with double bonds or with any heteroatom-containing functional groups, or (b) positively-or negatively-charged heteroatoms. The rule is also applicable to product ions observed in collision-induced dissociation.

Systematic identification of N‐acetylheparosan oligosaccharides by tandem mass spectrometric fragmentation

“…At this point it should be noted that the structural regularity of a GAG often makes interpretation of its MS/MS spectrum difficult. That is, in the above experiments, the m/z values observed for C ev and Z ev ions of the same saccharide length were the same, on the basis of the established ‘mass shift rule’ 21. For example, NAH hexasaccharide gave an apparently single fragment ion signal at m/z 378, which can be assigned to either C 2 or Z 2 ions (Fig.…”

Investigation of collision‐induced dissociations involving odd‐electron ion formation under positive electrospray ionization conditions using accurate mass

“…For any structure elucidation work based on tandem mass spectrometry (MS/MS), correct interpretation of the fragmentation pathways is the key for successful structure elucidation. While the fragmentation mechanisms in traditional electron impact (EI) and chemical ionization (CI) mass spectrometry have been well understood and documented,1 for the fragmentation mechanisms of collision‐induced dissociation (CID) under the modern atmospheric pressure ionization conditions, understanding is much less and there are no systematic reviews in the primary literature,2, 3 despite several reports of CID rationalization and empirical rules 2–4…”

Technical Challenges in Mass Spectrometry-Based Metabolomics

“…[71][72][73] Although a rule to account for mass shi s in fragmentations of even-electron organic ions has been proposed, 74) precise prediction of fragments produced by collision induced dissociation of target molecules continues to be challenging in computational mass spectrometry research. 73,[75][76][77][78] Since the databases of naturally occurring metabolites have been developed and enriched by methods such as in silico derivatization of chemical structure, 79,80) the prediction of tandem mass spectra data from the metabolite structure, based on some fragmentation rules, 75) quantum chemistry simulations as well as machine learning techniques 73) would be key technologies for metabolomics and computational mass spectrometry.…”