Negative-ion electrospray ionisation-mass spectrometry (ESI-MS) as a tool for analysing structural heterogeneity in kappa-carrageenan oligosaccharides.

Oligosaccharides, enzymically produced from kappa-carrageenan, have been investigated by electrospray ionisation mass spectrometry (ESI-MS). The technique was used without prior derivatisation of the oligosaccharide originally obtained by size-exclusion chromatography (SEC). The structure of the oligosaccharides was mainly 4-sulphated neocarrabiose (A-G4S) with an increasing length ranging from di- to dodecasaccharides. However, in the larger oligosaccharides, structural motifs deviating from the perfect alternating A-G4S structure were detected, i.e. (A2S-G4S). Although resulting in reduced signal intensity, samples to which NaCl was added also gave rise to reliable mass spectra. Desulphation was induced at elevated cone voltages and in acidic or alkaline salt solutions.