Gas‐phase fragmentation study of biotin reagents using electrospray ionization tandem mass spectrometry on a quadrupole orthogonal time‐of‐flight hybrid instrument

In this study, we evaluated, by electrospray ionization mass spectrometry (ESI‐MS) and collision‐induced dissociation tandem mass spectrometry (CID‐MS/MS) using a quadrupole orthogonal time‐of‐flight (QqToF)‐MS/MS hybrid instrument, the gas‐phase fragmentations of some commercially available biotinyl reagents. The biotin reagents used were: psoralen‐BPE 1, p‐diazobenzoyl biocytin (DBB) 2, photoreactive biotin 3, biotinyl‐hexaethyleneglycol dimer 4, and the sulfo‐SBED 5. The results showed that, during ESI‐MS and CID‐MS/MS analyses, the biotin reagents followed a similar gas‐phase fragmentation pattern and the cleavages usually occurred at either end of the spacer arm of the biotin reagents. In general we have observed that the CID‐MS/MS fragmentation routes of the five precursor protonated molecules obtained from the biotin linkers 1–5 afforded a series of product ions formed essentially by similar routes. The genesis and the structural identities of all the product ions obtained from the biotin linkers 1–5 have been assigned. All the exact mass assignments of the protonated molecules and the product ions were verified by conducting separate CID‐MS/MS analysis of the deuterium‐labelled precursor ions. Copyright © 2009 John Wiley & Sons, Ltd.