Comparison of the application of Debye-Huckel and specific ion interaction theories for the complexation of tungsten(VI) with ethylenediaminediacetic acid

Equilibrium of the reaction of tungsten(VI) with ethylenediaminediacetic acid (EDDA) has been investigated in aqueous solution of pH 7.5 and 25°C. All measurements have been carried out at different ionic strengths ranging from (0.1 to 1.0) mol dm −3 (NaClO 4 ). According to our results the metal to ligand ratio is 1: 1. Stability constants and stoichiometry of the complex have been determined from a combination of potentiometric and UV spectroscopic measurements. In this semi-empirical model, two parameters have been introduced in a Debye-Huckel type equation based on the Gauss—Newton nonlinear least-squares method and minimizing the sum of the squares of the errors. Comparison of the ionic strength effect on these complex formation reactions has been made using a Debye-Huckel type equation and Bronsted—Guggenheim—Scatchard specific ion interaction theory (SIT).