Determination of basic impurities in mixtures of hydrolysable salts

Abstract

A multi-parametric curve-fitting method for the determination of basic impurities present in solutions of hydrolysable salts is proposed. It consists in pH titration in isomolar titrand-titrant systems characterised by a high ionic strength. A suitably defined regression function of the Pade type enables the concentrations of the strong and weak acids present in solution to be found by an iterative procedure. The basicity, Δca=ca*–ca, of the salt in solutions is defined as the difference between the concentration of the strong acid added (ca*) and that calculated (ca) from titration data (Vj, pHj). A linear correlation between Δca and the relative error in the determination of a weak acid concentration (cL) was observed (a standard solution of the weak acid was added as a buffering agent in the system). The method proposed has been applied successfully to the determination of basic contaminants in mixtures of concentrated solutions of cadmium and magnesium chlorides.