Spectrophotometric study of a hafnium-hematein chelate

A spectrophotometric study of an analytically useful hafnium chelate of hematein is presented. The stoichiometry, the formation constant, the optimal pH range and the free energy of formation of the chelate are described. Beer's law is obtained in the range 3–25 μg of hafnium(IV).The red-brown chelate, of probable formula HfOhematein]₂, can be used for the colorimetric determination of hafnium in the presence of zirconium, if the molar concentrations of both metals are the same. The molar absorptivity of the hafnium chelate is 5.8·10⁴ 1 mole^-1 cm^-1 at 520 nm and pH 2.0 at room temperature.