Analysis of Maltose and Lactose by U-HPLC-ESI-MS/MS

Analysis of lactose and maltose and their discrimination from other disaccharides such as sucrose is an important and challenging task in food analysis. ESI-MS and MS/MS are a valuable detection methods for underivatized disaccharides, however the absence a distinctive ions and CID fragmentation patterns does not allow discrimination of stereoisomers without good chromatographic resolution. Among the many chromatographic approaches reverse-phase elution on porous graphitic carbon (PGC) appears then most performing and suited to ESI-MS spectrometry. After an overview on LC-MS analysis of oligosaccharides, in this chapter we focus on a recently developed U-HPLC-ESI-MS/MS approach, on PGC columns, able to separate and detect the disaccharides (lactose and maltose) in their anomeric forms, as formate adducts obtained directly in-column. Using a Paul trap to monitor adducts [M+HCOO]- at m/z 387 in ESI negative mode (MS^1) and CID fragment ion [M-H]- at m/z 341 (MS^2), the method offers low pg sensitivity in complex vegetable matrices.