MATRIX-ASSISTED LASER-DESORPTION IONIZATION MASS-SPECTROMETRY FOR THEANALYSIS OF MONOSULFATED OLIGOSACCHARIDES

Sulfated oligosaccharides are an important class of compounds in the f ield of glycobiology. Mass spectrometric analysis of these molecules i s challenging due to their readiness to dissociate in sample preparati on and their tendency to fragment during ionization. Moreover, their p resence in small quantity in biological systems poses additional probl ems. We report the development of a mass spectrometric method based on matrix-assisted laser desorption ionization (MALDI) in a time-lag foc using time-of-flight mass spectrometer for the analysis of monosulfate d oligosaccharides. It is found that coumarin 120 is an excellent matr ix for the analysis of monosulfated disaccharides, whereas the use of a mixture of coumarin 120 and 6-aza-2-thiothymine is very effective fo r the ionization of sulfated trisaccharides and tetrasaccharides inclu ding those containing N-acetylneuraminic acid. Molecular ions for a se ries of synthetic sulfo/sialo beta Gal(1 --> 3)GlcNAc and beta Gal(1 - -> 4)GlcNAc structures can thus be observed with subpicomole detection sensitivity using a uniform microcrystal matrix/sample preparation pr ocedure. It is demonstrated that, with this matrix formulation, the pr esence of a high amount of sodium chloride or sodium phosphate buffer, which is often the case for the HPLC fractionated samples, does not d eteriorate the MALDI performance. The analysis of mixtures containing different types of oligosaccharides is also examined. It is found that different classes of oligosaccharides require different matrix prepar ation methods. (C) 1997 Elsevier Science Ltd.