Chromatographic purification of stable isotopes of Ni, Cu, and Zn and their isotopic compositions in geological and biological reference materials†

Nickel (Ni), copper (Cu), and zinc (Zn) isotopes are used to study biogeochemical and environmental processes. Studies using multiple metallic isotopes are being conducted to advance knowledge of many processes in the Earth system. However, most chromatographic purification methods focus on a single element and studies of multiple metals require different chemical separation protocols. In this study, we developed a new three-step sequential chromatographic protocol that enables isotope studies of Ni, Cu, and Zn in a single sample and is applicable to diverse sample types. Isotope compositions were measured by MC-ICP-MS with different sample introduction systems (wet plasma for Cu and Zn; dry plasma for Ni). Instrumental mass bias was corrected by sample-standard bracketing (SSB) and internal doping with an isotope standard of similar mass. The Ni, Cu, and Zn yields were ∼99% for six geological and two biological reference materials. The δ⁶⁰Ni, δ⁶⁵Cu, and δ⁶⁶Zn values measured in this study were consistent with reported data within the analytical uncertainty. New isotope values in reference materials, including rock, mineral resources, soil, sediments, urban dust, sludge, and living organisms, are reported for Ni (n = 44), Cu (n = 24), and Zn (n = 17). This method can produce high-precision isotope data from various environmental samples, even with limited sample amounts. This work presents an improved method over existing approaches, opening potential applications for metallic stable isotopes in various research fields.