Differentiation and Relative Quantitation of Disaccharide Isomers by MALDI-TOF/TOF Mass Spectrometry

Saccharide isomer differentiation has been a challenge in glycomics, as the lack of technology to decipher fully the diverse structures of compositions, linkages, and anomeric configurations. Several mass spectrometry-based methods have been applied to the discrimination of disaccharide isomers, but limited quantitative analyses have been reported. In the present study, MALDI-LIFT-TOF/TOF has been investigated to differentiate and relatively quantify underivatized glucose-containing disaccharide isomers that differ in composition, connectivity or configuration. N-(1-naphthyl)ethylenediamine dihydrochloride (NEDC) was used as a highly sensitive matrix without matrix interferences in low mass range, thus yielding intense chloride-attached disaccharide ions [M + Cl]^-, which could be fragmented to give diagnostic characteristic fragment patterns for distinguishing these isomers. Three different types of disaccharide isomers were successfully relatively quantified in a binary mixture using the specific product ion pairs. Finally, this method was utilized to identify and relatively quantify two disaccharide isomers in Medicago leaf (maltose and sucrose) without numerous preparation steps. In general, this method is a fast, effective, and robust method for rapid differentiation and quantitation of disaccharide isomers in complex medium.