Characterisation of ι-carrageenans oligosaccharides with high-performance liquid chromatography coupled with evaporative light scattering detection

Enzymatically digested oligo-ι-carrageenans were separated with liquid chromatography, coupled to evaporative light scattering detection. As expected, compared to oligo-κ-carrageenans, the additional sulphate group in the neocarrabiose unit of ι-carrageenans significantly modified the separation mechanisms on ion-exchange chromatography, porous graphitic carbon and ion-pair chromatography. The oligomers were then isolated and characterised off-line with electrospray ionisation mass spectrometry in positive-ion mode. The tetrasaccharide, hexasaccharide and octasaccharide that were identified were associated with protonated heptylamine molecules whose number depended on the number of sulphate groups.