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 Padé type enables the concentrations of the strong and weak acids present in solution to be found by an iterative procedure. The basicity, Δc_a=c_a^*–c_a, of the salt in solutions is defined as the difference between the concentration of the strong acid added (c_a^*) and that calculated (c_a) from titration data (V_j, pH_j). A linear correlation between Δc_a and the relative error in the determination of a weak acid concentration (c_L) 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.