On the Rodil–Vera method for determining ion activity coefficients

Abstract

The basic principles of the method that Rodil and Vera described [E. Rodil, J.H. Vera, Fluid Phase Equilib. 205 (2003) 115–132] to calculate the liquid junction potential and to deduce ion activity coefficients from potentiometric data are critically discussed. It is shown that their procedure is based on an inconsistent loop, and the ion activity coefficients it yields are only an artefact of arbitrary assumptions, with no relationship to the real values, which remain unknown. To provide evidence of this fact, an identical procedure is applied to virtual data referring to a simulated potentiometric experiment with a hypothetical electrolyte whose ion activity coefficients are known; the procedure proves to be unable to recover these activity coefficients. The failure is irremediable and affects all activity coefficients of single ions, which have been reported by Vera and co-workers in the numerous papers they have published so far, whose conclusions lack any scientific support.