Hafnium isotope analysis of mixed standard solutions by multi-collector inductively coupled plasma mass spectrometry: an evaluation of isobaric interference corrections

摘要

The Lu-Hf isotope system is widely used to decipher the crustal evolution and mantle differentiation of the Earth. The most critical point in obtaining accurate Hf isotope data is to correct the isobaric interferences of Yb and Lu imposed on the 176Hf peak. In this study, we tested the validity of within-run correction protocol using MC-ICP-MS analysis of Hf standard solutions doped with Yb and Lu. We found that the use of carefully selected Yb isotopic composition in the literature resulted in more reliable 176Hf/177Hf ratio. The 176Hf/177Hf ratios analyzed for a series of mixed Hf+Yb+Lu standard solutions could be quite accurately corrected for the mass bias and isobaric interferences. The systematic decreasing trend in the corrected 176Hf/177Hf ratios with increasing Yb/Hf ratios, however, indicates that the mass bias effect cannot be completely removed by the exponential law for samples high in Yb. A close correlation of the calculated 176Yb/177Hf and 176Lu/177Hf ratios with the gravimetric values sheds light on the direct determination of inter-elemental isotope ratios without chemical purification.