Determination of Free Acid by Automated lon Exchange-Colorimetry

Abstract: Savannah River Laboratory E. I. du Pont de Nemours & Co. Aiken S. C. 29801 THE DETERMINATION of free acid in the presence of hydrolyzable ions has always been difficult. Hydrolyzable ions are normally removed by complexing agents. Eder (1) critically examined 12 methods for determining free acid and found the fluoride method described by Craig (2) the most satisfactory. More recently Booman et al. (3) have reviewed methods using potassium fluoride or oxalate (4-7) and potassium ferrocyanide (8). The oxalate procedure is used in this laboratory but requires prior knowledge of the species of hydrolyzable ion present and the pH of the end point to give minimum bias. The method is not readily adaptable to solutions containing more than one hydrolyzable ion in varying concentrations. Recently free acid (0.05-0.M) had to be determined in concentrated solutions of LiCI containing hydrolyzable ions. When developing an automated method to solve this problem a method evolved for determining free acid in solutions containing a variety of hydrolyzable ions. In this method hydrolyzable ions are removed by ion exchange and the unaltered free acid is determined colorimetrically. This paper describes the method and its applicability in determining free acid in both nitric acid and hydrochloric acid systems containing hydrolyzable ions such as La3+ Al3+ Th4+ and UO22+. . . .

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