Fractionation of Alginates by Precipitation with Calcium and Magnesium Ions.

Abstract

Fractional precipitation of alginate with Ca ions in the presence of magnesium chloride leads to separation of the alginate into fractions with different uronic acid composition. A similar fractionation may also be achieved with magnesium chloride alone, in water or in the presence of small amounts of ethanol. In both cases the precipitates are enriched in guluronic acid-rich molecules. In the former case the fractionation is probably due to higher affinity for Ca ions of the guluronic-rich molecules in solutions of Ca and Mg ions, while in the latter case a fractional salting-out of magnesium alginate in magnesium chloride solutions is responsible for the fractionation. These fractionation methods have considerable advantages compared to the methods earlier described.