Structural determination of fructooligosaccharides and raffinose family oligosaccharides using logically derived sequence tandem mass spectrometry†

Fructooligosaccharides (FOS) and raffinose family oligosaccharides (RFOs) are two highly abundant water-soluble carbohydrates in plants. The typical procedures for the FOS and RFO structural determination using mass spectrometry involve permethylation, followed by the hydrolysis of the permethylated oligosaccharides into monosaccharides, and then the identification of linkage positions using GC mass spectrometry. However, the determination of linkage position sequence is not straightforward, thus this method is limited to small oligosaccharides or oligosaccharides with simple linkages. In this study, we employed a new mass spectrometry method, logically derived sequence tandem mass spectrometry, to determine the structures of FOS and RFOs. We first showed that the monosaccharide and disaccharide CID spectra of aldohexose and ketohexose can be rationalized using dissociation mechanisms. Then we demonstrated that the linkage positions of FOS and RFOs can be identified, the sequence of the linkages can be determined, and the ketohexose and aldohexose in FOS and RFOs can be differentiated, suggesting this new method is useful for structural determination of FOS and RFOs.