Determination of zirconium, niobium, hafnium and tantalum at low levels in geological materials by inductively coupled plasma mass spectrometry

Abstract

The determination of Zr, Nb, Hf and Ta in geological materials by inductively coupled plasma mass spectrometry is reported. The relative merits of sample preparation using three fusions, with LiBO₂, KHF₂ and K₂B₄O₇, were compared and the first, coupled with analyte separation using precipitation with cupferron, was found to be preferred. Calibration was carried out using internal standardisation with Ru for Zr and Nb and Re for Hf and Ta. This technique compensates effectively for matrix effects arising from the presence of elements such as U, the one exception found being suppression by Al at the 1000 µg ml^–1 level on Zr and Hf. This is further reason to employ separation with cupferron as Al is recovered at an efficiency of only 1–3%. The method yields determination limits of 0.4 µg g^–1 for Zr and 0.02 µg g^–1 for Nb, Hf and Ta. The results are shown to be accurate with respect to international reference materials. Relative standard deviations were in the range 2–4%.