Isolation of κ-carrageenan oligosaccharides using ion-pair liquid chromatography––characterisation by electrospray ionisation mass spectrometry in positive-ion mode

Abstract

Oligo-κ-carrageenans participate as elicitors in the cell–cell recognition process in marine plants. Analytical methods can be usefully applied to gain insight into the biochemistry of these biological processes. Therefore, enzymatically digested oligomers of κ-carrageenans have been separated and isolated on a Spherisorb ODS1 (250 × 4 mm i.d., particle size 5 μm) column using ion-pair liquid chromatography coupled with an evaporative light scattering detector. Heptylamine (5 mM, pH 4) has been selected as the ion-pairing agent and MeOH as the organic modifier in a gradient mode. Overloading the column with 1 mg of the mixture, the chromatographic mechanism presented adequate stability. The mobile phase of each isolated oligomer was evaporated and the residue was infused into an electrospray ionisation mass spectrometry (ESIMS) in positive-ion mode with 4:1 MeCN–water as mobile phase. Each ESIMS spectrum presented ions consisting of the oligomer attached with a number of heptylammonium ions depending on the molecule size. In addition, the different m/ z values permitted direct detection of the oligomers in ESIMS positive-ion mode. The analytical method developed separated the oligomers up to dotriacontasaccharide.