SIMULTANEOUS DETERMINATION OF COBALT, NICKEL AND IRON BY MULTIWAVELENGTH SPECTROPHOTOMETRY

A method for the simultaneous spectrophotometric determination of cobalt, nickel and iron based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide is proposed. The absorption curves of these complexes overlap severely in the scanning range 390-510 nm. The analyte concentrations are calculated by a least squares fit of the pure spectra to the mixture spectra, which therefore makes the simultaneous determination of these metallic ions possible without tedious pretreatment. The detection limits afforded by the proposed method range from 0.05 mu g/ml for Fe and Ni to 0.1 mu g/ml for Co. Root-mean-squared errors of prediction of 0.085 mu g/ml for Co, 0.048 mu g/ml for Ni and 0.1172 mu g/ml for Fe were obtained using the wavelength range 400-510 nm and 0.147 mu g/ml for Co, 0.107 mu g/ml for Ni and 0.127 mu g/ml for Fe using the wavelength range 420-434 nm. The effect of interferences is studied and the proposed method is applied to analysis for the above elements in synthetic samples and real samples, such as biological materials and alloys.