Application of Electrospray Tandem Mass Spectrometry in Sequence Analysis of Oligosaccharides

Analysis of oligosaccharide structure and sequence plays a significant role in unravelling the biological function of glycoconjugates. Electrospray ionization mass spectrometry(ESI-MS) is an important tool for the qualitative and quantitative analysis of oligosaccharides with high sensitivity, high precision and high speed. Some oligosaccharides with different structural characteristics, such as N-glycans, chondroitin sulfate oligosaccharides, human milk oligosaccharides, chitooligosaccharide, alginate oligosaccharides, carrageenan oligosaccharides and sulfated fucan oligosaccharides are discussed in this paper. The application techniques of ESI-MS and fragmentation rule of oligosaccharides in the sequence analysis of the main chain, branch sites, substitution positions of sulfate groups, as well as the monosaccharide composition and the degree of polymerization are summarized. The types of monosaccharide composition can be obtained primarily based on the adjacent m/z difference of B/C fragment ions. The resolution and ionization efficiency of oligosaccharides can be improved by combination with chromatography separation techniques or derivatization methods, and then the molecular weight and degree of polymerization of oligosaccharides can be measured. The information of reducing residue and partial sequence of oligosaccharides can be obtained by means of tandem mass spectrometry and characterized derivatization of the reducing end. The types and particular locations of residues can be determined according to their specific fragment ions and abundance. In addition, the branches of oligosaccharide usually occur glycoside bond breakage as a unit or produce D ions, which can be used to determine the branch points. The sulfate groups in different sites can be obtained by their specific cross-ring fragments. The summarization of fragmentation rule of oligosaccharides in ESI-MS provides a guidance to the structure and sequence analysis of unknown oligosaccharides.