Purification of Hf in silicate materials using extraction chromatographic resin, and its application to precise determination of 176Hf/177Hf by MC-ICP-MS with 179Hf spike

Abstract

A two-stage column purification method for Hf from Zr and other elements in silicate samples using the extraction chromatographic resin, UTEVA has been developed. In the first column, using an anion-exchange resin, AG 1X8, Hf, Zr and Ti were collected. In the second, using UTEVA, and after eliminating F⁻ by evaporation with HClO₄ and re-dissolution with H₂O₂–HNO₃, Hf was purified from Ti and Zr, based on characteristic of the UTEVA resin that Hf distribution coefficient (K_d) decreases from 770 to 40, while K_d of Zr decreases less from 890 to 200, in 9 and 6 mol l⁻¹ HNO₃, respectively. The recovery yield of Hf was ∼88% and total blank was ∼4 pg. A MC-ICP-MS Hf isotope ratio determination method was also developed, which uses ¹⁷⁹Hf spike for simultaneous determination of the Hf concentration and ¹⁷⁶Hf/¹⁷⁷Hf ratio. Combining the chemistry and ICP-MS techniques, ¹⁷⁶Hf/¹⁷⁷Hf ratios in silicate reference materials were determined with and without the spike, which gave identical results, showing the applicability of this method.