Analysis of carbohydrates by fast atom bombardment mass spectrometry: 2—Influence of the matrix and the nature of the alkaline cations in the attachment process of an alkaline cation to a disaccharide molecule

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Abstract
The fast atom bombardment (FAB) ionization process of a non‐reducing disaccharide by an attachment reaction with an alkaline cation has been investigated according to the nature of both the matrix (glycerol, diethanolamine, triethanolamine) and the alkaline cation (lithium, sodium, potassium, rubidium, caesium). We have established that one way of forming the cationized disaccharide molecular ions, [disaccharide‐cat]+, is by a desolvation reaction from the cationized solvated disaccharide molecular ions, [disaccharide‐cat‐matrix]+. This process, which has been established by mass‐analysed ion kinetic energy (MIKE) spectral analysis of the solvated species, is shown to be drastically affected by the nature of the involved matrix but only slightly by the alkaline cation. The variations in the relative abundances of the disaccharide cationized molecular ions compared to their solvated clusters in the FAB mass spectra, due to the matrix employed, have been explained according to the unimolecular dissociation of the solvated clusters examined by MIKE analysis. However, the variations in the abundance of the disaccharide cationized molecular ions in relation to the alkaline cation used—a higher sensitivity has been observed for lithium, sodium and potassium alkaline cations—have been explained in terms of the cations available at the target surface for the attachment process to the sugar molecule, and by a ligand exchange reaction between the matrix and the disaccharide.