Suppression of sialylated by sulfated oligosaccharides in negative MALDI-FTMS

Sialylated oligosaccharides are suppressed by sulfated oligosaccharides during matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The sialylated oligosaccharide may be suppressed by as much as a factor of ten to twenty. This suppression factor is constant over a large concentration range. As both sialylated and sulfated (or anionic) oligosaccharides are found together in many biological systems, the suppression has important consequences in the analysis of these compounds. Methods for overcoming the effect of suppression without laborious separation are provided.