Ion exchange chromatography and high precision isotopic measurements of zirconium by MC-ICP-MS

Abstract

This paper presents a new technique for the precise and accurate determination of Zr isotopic compositions in geological samples. Following the separation of Zr from the geological matrix with a two-stage anion-exchange procedure the isotopic compositions are measured by multiple collector ICP-MS. Replicate dissolutions of the carbonaceous chondrite Allende with <100 ng Zr yield a long-term reproducibility of ±39 ppm for ⁹¹Zr/⁹⁰Zr, ±25 ppm for ⁹²Zr/⁹⁰Zr, and ±82 ppm for ⁹⁶Zr/⁹⁰Zr. Analyses of synthetic standards solutions show that isobaric interferences of Mo and Ru can be adequately corrected for Mo/Zr ≤ 0.5 × 10⁻² and Ru/Zr ≤ 1 × 10⁻² and such elemental ratios are readily achieved for geological samples following the anion-exchange procedure. It is furthermore shown that the chemical separation technique effectively isolates Zr from Ti, Cr, and Fe. This is important because the Zr isotope data can be readily biased by the argides of these elements. The presented method has been successfully applied to terrestrial igneous rocks, meteorites and mineral separates including samples with high Ti contents.