Tracer diffusion of some metal ions and Metal–EDTA complexes in aqueous sodium chloride solutions

Abstract

Taylor dispersion and differential refractometry are used to measure the tracer diffusion coefficients of FeEDTA^2–, NiEDTA^2–, CuEDTA^2–, ZnEDTA^2– and LaEDTA^– complexes in 0.01, 0.05 and 0.10 mol dm^–3 aqueous NaCI solutions at 25 °C. A comparison is made with the tracer diffusion coefficients of Fe²⁺, Ni²⁺, Cu²⁺, Zn²⁺, La³⁺ and H₂EDTA^2– ions, which are also measured. The limiting mobilities of the species are estimated by extrapolating the tracer diffusion coefficients to zero ionic strength. Detecting the dispersed samples by differential refractometry allows the diffusion coefficient of supporting electrolyte and the cross-diffusion coefficient between the supporting and tracer electrolytes to be determined in addition to the tracer diffusion coefficient. Radiochemical labels are not required.