Analysis of underivatized oligosaccharides by liquid chromatography/electrospray ionization tandem mass spectrometry with post-column addition of formic acid

Underivatized oligosaccharides were analyzed by electrospray ionization (ESI) using a linear ion trap mass spectrometer in the negative ion mode with post-column addition of an aqueous solution of formic acid. Under these conditions all oligosaccharides showed the presence of the corresponding formate adduct [M + HCOO](-) with high intensity and easy subsequent low-energy collision-induced dissociation (CID) fragmentation using successive MS(n) experiments. A careful examination of the mass spectra obtained from these MS(n) experiments pointed out some significant differences useful to identify and quantify the single components in mixtures of coeluted disaccharides. This new sensitive and rapid method was successfully applied to the quantification of oligosaccharides in some juices minimizing sample handling.