The determination of strong and weak acidic groups in sulfite pulps

Abstract

Two methods are presented for the determinations of the sulfonate and carboxylate groups in sulfite pulps. One method involves the initial conversion of the groups to their magnesium salts. A differentiation of the two groups is then made based upon the liberation of magnesium from the carboxylate groups by 0.01 M acetic acid followed by the elution of magnesium from the sulfonate groups by 0.1 M hydrochloric acid. The elution by acetic acid is, however, not completely specific for the carboxylate groups and a small correction must be made. In the second method, the groups are converted to hydrogen form and are then titrated conductometrically with sodium hydroxide in the presence of 0.001 M sodium chloride. Inflexion points mark the end of titration of the strong acids and the total acids. Good agreement was obtained between the two methods but conductometric titration is preferred for its directness and simplicity.