Differentiation of DiastereomericN-Acetylhexosamine Monosaccharides Using Ion Trap Tandem Mass Spectrometry

A quadrupole ion trap mass spectrometer equipped with electrospray ionization was used to distinguish three diastereomeric monosaccharides, N-acetylglucosamine, N-acetylgalactosamine, and N-acetylmannosamine. The saccharides were derivatized to form the metal complex [CoIII(DAP)2HexNAc]Cl3 which, when collisionally activated, produced dramatically different product ion spectra. The product ion spectra generated for the three monosaccharide diastereomers were then used to confirm the stereochemistry of N-acetylhexosamines from a hydrolyzed oligosaccharide. Finally, the origin of each product ion was determined through isotopic labeling studies, and mechanisms were proposed which explain each resulting dissociation.