Simultaneous kinetic determination of zinc, magnesium, copper and nickel by a ligand substitution reaction
Abstract
The rate of the ligand substitution reaction between calmagite [3-hydroxy-4-(2-hydroxy-5-methylphenylazo)-naphthalene-1-sulphonic acid] complexes of Zn(II), Mg(II), Cu(II) and Ni(II) and EDTA was studied at 25.0 °C and pH 9.5 by a stopped-flow spectrophotometric technique. The reactions were first order in calmagite complexes and in incoming ligand for Zn, Cu and Ni, while a zero-order dependence on EDTA was observed for Mg. The change of absorbance at 500 nm, accompanying the substitution reaction, was used for the determination of the metal ion. For multi-component mixtures such as Zn, Mg and Cu or Ni, the absorbance change during the reaction was separated kinetically for each component, in the reactivity order Zn > Mg > Cu ≈ Ni, so that metal ions at concentrations down to 10–6M could be determined simultaneously. The method was applied to the analysis of standard mixtures and samples of river water, tap water and mineral waters.