The influence of dissociation on simultaneous determination of zirconium and hafnium with Xylenol Orange

The molar absorptivities of the zirconium and hafnium Xylenol Orange (1:1) complexes are said to be similar in the acidity range 0.1-2.0M HCl. However, the absorbances obtained for the zirconium-Xylenol Orange complex in the acidity range 0.5-2.0M HCl are much higher than those for the same concentrations of hafnium. The absorbance differences are generally due to the higher stability of the zirconium complex at such acidities. Calculations based on the conditional stability constants of these complexes show the influence of dissociation on the results of simultaneous determination of zirconium and hafnium with Xylenol Orange.