On the Estimation of Alginic Acid in Seaweeds by the Method of Colloid Titration

抄録

This method is based on the theory that positive polymer ions combine stoichiometrically with negative ones in a dilute solution at a definite pH value. A definite amount of 0.005 N solution of a positive colloid like N-trimethylated glycol chitosan is added to a solution or an extract (pH ca. 7) containing alginic acid, the excess of the added positive colloid being titrated with a standard solution (0.0025 N) of a negative one such as potassium salt of polyvinyl sulfonate. The end-point of this titration is indicated by the color change of toluidinc blue or the sudden precipitation of reactants. Whenever an extract contains some protein, however, it is necessary to digest this protein by treating the extract with pepsin prior to titration. The amounts of alginic acid can be calculated from the value, which is obtained by deducting the results of several titrations from the mean-titre of blank experiments.