High-precision copper isotopic analysis using a Nu Sapphire MC-ICP-MS

Abstract

Here we present an analytical method for Cu isotopic measurement using standard-sample bracketing on a Nu Sapphire multi-collector inductively coupled plasma mass spectrometer. The effects of Cu concentration and HNO₃ molarity mismatch between the standard and the sample, as well as the presence of matrix elements have been evaluated. Intermediate precision of better than ±0.030‰ for δ⁶⁵Cu (2SD) was routinely obtained on NIST SRM 3114 and NWU-Cu-A. Accurate measurements were achieved when C_Na/C_Cu < 0.5, C_Ti/C_Cu, C_Fe/C_Cu and C_Co/C_Cu < 1, C_Ni/C_Cu < 3 and C_Zn/C_Cu < 10. High-precision Cu isotopic data were determined for nineteen geological reference materials, including igneous rocks, sedimentary rocks, metamorphic rocks and chalcopyrite, with an overall range of ∼0.44‰ (−0.056‰ to 0.384‰), nearly 15 times the current analytical precision. The Cu isotopic data of these reference materials can be used for future interlaboratory comparisons.