Analysis of binary and ternary mixtures of cobalt,nickel and copper by differential kinetic methods based on ligand substitution reactions

The methods are based on displacement of pyridoxal thiosemicarbazone from its complexes with cobalt, nickel and copper(II) with DCTA. The reactions are monitored spectrophotometrically at 425 nm. The Ni/Cu and Co/Ni/Cu mixtures are analyzed by the single-point method and the Co/Ni and Co/Cu mixtures by the logarithmic extrapolation method. In all determinations the relative standard deviation is <3%, at the μg ml^?1 level.