Distinguishing of linkage isomers of lactotetra oligosaccharides by using the relative ion intensity analysis of post-source decay fragment ions in curved-field reflectron matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The native oligosaccharides of lacto-N-neotetraos (Gal beta1-4GlcNAc beta1- 3Gal beta1-4Glc; LNnT) and lacto-N-tetraose (Gal beta1-3GlcNAc beta1-3Gal b eta1-4Glc; LNT) were analyzed by using curved-field reflectron matrix-assis ted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Since a curved-field reflectron TOFMS enables a simultaneous focusing of a wide mass range of metastable fragment ions, the relative ion intensit ies in the post-source decay (PSD) mass spectra can be discussed. The PSD m ass spectra of LNnT and LNT were distinguishable in their relative ion inte nsities. In the case of LNT, beta -elimination could occur in the N-acetyl glucosamine (GlcNAc) at the C-3 position, which was bonded by galactose (Ga l); however, it did not occur in LNnT. The 3-O elimination caused a differe nce in the relative ion intensities in the PSD mass spectra of LNnT and LNT . The beta1-3 glycosyl linkage cleaved more easily than the beta1-4 glycosy l linkage in the MALDI-PSD fragmentation. An analysis of the relative ion i ntensities in the MALDI-PSD mass spectra of oligosaccharides was very usefu l for distinguishing the linkage isomers and for characterizing the types o f glycosyl linkages.