Simultaneous derivative spectrophotometric determination of cobalt(II) andnickel(II) by dithizone without extraction

Dithizone (Dz), a common extractive-photometric ligand for Co(II) and Ni(II ), has been dissolved in the water-miscible solvent tetrahydrofurane (THF) so as to constitute a reagent for both metals in aqueous phase without extr action. Complex formation was complete for both metals at pH 12.0 (adjusted by aqueous NH3) within 30 min, and the complexes were stable for at least 2 h. First-derivative spectra of the metal dithizonates (singly or as binar y mixtures) were preferred to ordinary spectra, because working wavelength determination was more precise and spectral overlap was less. Two wavelengt hs at which the spectral overlap was minimum were selected as analytical wa velengths, i.e. 620 nm for Co and 740 nm for Ni, and the calibration curves drawn with zero-to-peak values as a function of concentration were linear for these wavelengths. Thus, the total D-1 values at 620 and 740 nm of the mixtures were used to determine Co and Ni concentrations. The relative stan dard deviation (R.S.D.) for the analysis of Co (3.0 mg l(-1)) individually was 3.5%, and for its admixture with Ni (3.5 mg l(-1)) was 3.5%. The R.S.D, for the analysis of Ni (5.9 mg l(-1)) individually and for its admixture w ith Co (1.8 mg l(-1)) were 5.5 and 5.8%, respectively. The linear range in D-1 evaluation was between 5.0 x 10(-6) and 1.0 x 10(-4) M for Co and 2.0 x 10(-5)-2.0 x 10(-4) M for Ni. Interference analysis was performed for indi vidual metal (Co or Ni) determinations. Finally, the method has been applie d to a Ni-Cr-based dental alloy (Wiron 99) successfully. (C) 2000 Elsevier Science B.V. All rights reserved.