A method for the simultaneous spectrophotometric determination of cadm
ium, copper and zinc based on the formation of their complexes with 1,
5-bis(di-2-pyridylmethylene)thiocarbonohydrazide is proposed. The abso
rption curves of these complexes overlap severely in the scanning rang
e 380-480 nm. The analyte concentrations are calculated by a least squ
ares fit of the pure spectra to the mixture spectra. A linear determin
ation range of 0.1-1.7 mug/ml for cadmium, 0.1-1.3 mug/ml for copper a
nd 0.2-1.2 mug/ml for zinc were obtained. The effect of interference w
as studied. The method has been applied to the determination of these
metal ions in various type of materials.