Structural characterization of pyridylaminated oligosaccharides derived from neutral glycosphingolipids by high-sensitivity capillary electrophoresis-mass spectrometry

High-sensitivity capillary electrophoresis-electrospray ionization quadrupole ion trap time-of-flight mass spectrometry (CE-ESI-QIT-TOF MS) was developed to structurally characterize four kinds of pyridylaminated (PA) oligosaccharides, i.e., lactose (Lac)-PA, globotriose (Gb₃)-PA, globotetraose (Gb₄)-PA, and IV³ αGalNAc-Gb ₄ (Forssman antigen)-PA, derived from neutral glycosphingolipids. The CE-MS system included the head-column field-amplified sample stacking (HC-FASS) method for effective sample injection into a capillary column in CE, a sheathless interface between CE and a mass spectrometer, and MS and tandem MS (MS²) measurements with narrow mass range repeated high-speed switching. The total sensitivity of the developed CE-MS system was about 20 000 times higher than that of the conventional CE-MS system consisting of pressure injection, a sheath-flow interface, and a wide mass range measurement. The MS and MS² spectra of the four PA-oligosaccharides at a concentration of 25 amol/μL in mixtures (each 250 amol/10 μL in a tube) clearly showed protonated molecular ions ([M + H]⁺) and the fragment ions responsible for the sequential elimination of saccharides. The developed CE-MS system is a powerful method for the structural characterization of glycosphingolipids extracted from very small amounts of biological materials and could be extended to the structural characterization of oligosaccharides derived from glycoproteins.