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Publisher Summary This chapter discusses practical aspects of fast atom bombardment–mass spectrometry (FAB–MS) and electrospray–mass spectrometry (ES–MS), including data interpretation, and describes examples of experimental strategies incorporating all three mass spectrometric methods, which are best suited to the analysis of glycoproteins, complex carbohydrates (including glycolipids), and glycosaminoglycans, respectively. In ES–MS technique a stream of liquid containing the sample of interest is injected directly into the ES source where the sample molecules are stripped of solvent, leaving them as multiply charged species whose charges reflect the number of functional groups that can be protonated (positive ion mode) or deprotonated (negative ion mode) at the pH of the carrier liquid. Two fragmentation pathways dominate carbohydrate FAB-MS, namely, A-type cleavage and β cleavage. A-type cleavage occurs on the nonreducing side of glycosidic bonds to give oxonium-type fragment ions and is the dominant pathway for permethyl and peracetyl derivatives. Cleavage is favored at amino sugar residues. A-type fragment ions are extremely helpful for structure assignments. β cleavage also involves glycosidic fission but, because a hydrogen transfer accompanies bond breakage, no charge is produced at the actual cleavage site as occurs during A-type cleavage. |
