SENSITIVITY IMPROVEMENT IN THE ANALYSIS OF OLIGOSACCHARIDES BY ONLINEHIGH-PERFORMANCE ANION-EXCHANGE CHROMATOGRAPHY ION-SPRAY MASS-SPECTROMETRY

The on-line coupling of high-performance anion-exchange chromatography (HPAEC) with ion spray mass spectrometry, for the analysis of neutral and acidic oligosaccharides, is described. On-line desalting is perfo rmed by a cation-exchange membrane system which replaces sodium for hy dronium ions from the effluent stream by means of either electrolysis of water or a combination of electrolysis and pneumatically supplied s ulphuric acid, In contrast to formerly described systems no booster pu mp between the cation-exchange system and the ion spray interface is n eeded, due to the almost complete absence of back-pressure. The on-lin e removal of sodium ions prior to the interface by means of electrolys is, and use of ion spray as an ionization technique, enables the routi ne use of gradients of sodium acetate up to a total sodium concentrati on of 0.6 M. After optimization of the HPAEC/MS system molecular mass determination could be obtained at concentrations down to 3 mu g/mL (2 0 ng of each compound) for alpha-1, 4-glucose oligomers up to a degree of polymerization of 7 (DP7). For maltodextrines the applicable mass range could be extended to over 3000 Da by the detection of at least D P20, as the doubly charged disodiated molecule. A series of galacturon ic acid oligomers could be detected up to DP4 at a concentration of 10 mu g/mL (67 ng per compound), using a sodium acetate gradient increas ing to a total sodium concentration of 0.6 M. (C) 1998 John Wiley & So ns, Ltd.