• edible seaweeds;
  • β-d-mannuronic acid and α-l-guluronic acid ratio;
  • ion-exchange chromatography;
  • LC-MS


A high-performance liquid chromatographic (HPLC) method is described for determination of the ratio of β-d-mannuronic acid to α-l-guluronic acid (M/G ratio) in dietary fibre of edible seaweeds. Total dietary fibre (TDF) content was determined gravimetrically. The TDF fraction was hydrolysed with 12 m and 1 m H2SO4, then neutralized with AG 4 × 4 resin. The uronic acids were separated in a Tracer Extrasil SAX 5 µm column (25 cm × 4 mm) at 35°C, with 2 mm KH2PO4 containing 5% methanol as mobile phase at a flow rate of 1.5 mL/min. The detection wavelength was UV 210 nm. The chromatographic identifications of β-d-mannuronic acid and α-l-guluronic acid were confirmed by liquid chromatography–mass spectrometry (LC-MS). The method precision was 1.4% for β-d-mannuronic acid and 3.5% for α-l-guluronic acid. The method was used to determine M/G ratio in canned seaweeds (Saccorhiza polyschides and Himanthalia elongata) and in dried seaweeds (H. elongata, Laminaria ochroleuca, Undaria pinnatifida, Palmaria sp. and Porphyra sp.). Copyright © 2003 John Wiley & Sons, Ltd.