General equation for determining the dissociation constants of polyprotic acids and bases from additive properties. Part I. Theory

Measured additive properties of polyprotic acids and bases as functions of the pH of the solution can be used for the determination of the dissociation constants. A rigorous general equation is derived in this paper for this purpose. The equation relates the additive property of the acid or base to the dissociation constants, the limiting values and activity coefficients of the solute species, and to the pH of the solution. The equation is used to obtain the dissociation constants by fitting it to the experimental data in a nonlinear least-square fitting procedure. Overlapping dissociation constants pose no problem in this method. Applications to spectrophotometry and reversed-phase high performance liquid chromatography are presented in a following paper (Part II of this series). (C) 1999 Elsevier Science B.V. All rights reserved.