Accurate and precise determination of Lu and Hf contents and Hf isotopic composition at the sub-nanogram level in geological samples using MC-ICP-MS

Abstract

We describe protocols for highly reproducible analysis of Lu and Hf contents and Hf isotopic composition at sub-nanogram levels in geological samples by MC-ICP-MS. Powdered samples were spiked with a ¹⁷⁶Lu–¹⁸⁰Hf enriched tracer and completely digested using conventional HF, HNO₃ and HClO₄ acid dissolution protocols. Fluoride salts were dissolved during a final H₃BO₃ digestion and chemical purification was performed using a single Eichrom Technologies Ln resin. All measurements were carried out on a Neptune Plus MC-ICP-MS employing an Aridus II desolvator. In order to demonstrate the robustness of the proposed protocol, six rock reference materials (RMs) were analysed, spanning various rock types with very low Lu and Hf contents (from nanogram to sub ng g⁻¹ levels). The results are in good agreement within uncertainty with published values for the analysed RMs. Relative to other approaches and low-blank levels, this protocol has great potential for Lu–Hf analysis of low volume (100–500 mg) samples in geochemistry, cosmochemistry and environmental sciences (e.g., peridotite, garnet, meteorites, dust, etc.).