Positive ion MALDI-TOF mass spectra are more suitable than negative ion spectra to characterize sulphated glycosaminoglycan oligosaccharides

Matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) is increasingly used in the field of carbohydrate characterization. The majority of oligosaccharides can be investigated with only a minimum extent of fragmentation. However, significant but unwanted sulphate loss occurs if the negative ion MALDI mass spectra of sulphated carbohydrates are recorded. We will show here by using differently sulphated oligosaccharides of the chondroitin sulphate (CS) type that this problem can be minimized by recording the positive ion spectra in the presence of the common MALDI matrix DHB (2,5-dihydroxybenzoic acid). Although the sensitivity of the positive ion spectra is reduced in comparison to the negative ion spectra, the reduction of the sulphate loss is a major advantage – particularly regarding the analysis of mixtures.

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► Glycosaminoglycans (GAGs) are acidic polysaccharides – often sulphated.
► Sulphate loss is an important, but unwanted fragmentation in the mass spectra of GAG.
► Positive ion MS leads to less pronounced sulphate loss than negative ion MS.
► Positive ion MS is only slightly less sensitive.
► Reduced sulphate loss is a significant advantage for mixture analysis.