Identification of anomeric configuration of underivatized reducing glucopyranosyl-glucose disaccharides by tandem mass spectrometry and multivariate analysis

The possibility of discrimination of the anomeric configuration (alpha or beta) of underivatized reducing glucopyranosyl-glucose disaccharides, using a hybrid mass spectrometer Q-TOF 2 (Micromass), a linear ion trap LXQ (Thermo), and a triple quadrupole Quattro (Micromass) with an electrospray source (ESI) was investigated. Differences observed in the relative abundances of specific product ions obtained from collisionally induced dissociation of the [M + Li]+ adducts were statistically analyzed, and discriminant analysis was performed. MANOVA has shown that anomeric configuration has influence on the combined dependent variables (relative abundances of m/z product ions) in all the three mass spectrometers used (Q-TOF 2, LIT, and QqQ). Discriminant analysis has shown that, in all instruments, it is possible to discriminate anomeric configurations and to build a diagnostic model. These diagnostic differences are even more relevant considering that no derivatization procedures are needed for obtaining this structural information. The Q-TOF 2 instrument has been shown to give data that allowed us to build a model with better discriminant power (Wilks' lambda value of 0.014) followed by the QqQ instrument (Wilks' lambda value of 0.029) and the LIT instrument (Wilks' lambda value of 0.037).