Accurate Determination of Cu Isotopes in Bronze by fsLA-MC-ICPMS

The Cu isotopic compositions of bronze artifacts can be used as a powerful archaeological tracer and provide valuable information regarding metal provenance and ore types. In this study, we investigated the feasibility of in-situ Cu isotopic analysis in bronze by matrix-matched and non-matrix-matched calibration using femtosecond laser ablation multiple collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS). Precise and accurate delta Cu-65 values of bronze can be obtained by using QT13 bronze as a matrix-matched standard. However, inaccurate delta Cu-65 values were obtained when bronze samples were calibrated by using pure copper as a non-matrix-matched standard (up to 0.44% deviation). The matrix effect can be significantly suppressed after applying a wet plasma condition during the fsLA-MC-ICP-MS analysis. Furthermore, bronze QT13 could serve as a potential matrix-matched reference material for in-situ Cu isotopic measurements of ancient bronze artifacts. The homogeneity test demonstrates that QT13 has a satisfactory homogeneous delta Cu-65 composition and is an appropriate material for calibrating Cu isotope ratio in bronze. Solution nebulizer (SN)-MC-ICP-MS analysis of QT13 bronze produced a mean delta Cu-65 value of 0.05 +/- 0.03% (2SD, n=38), which is suggested as the recommended delta Cu-65 value. The LA-MC-ICP-MS analyses of QT13 during eight months yielded highly consistent delta Cu-65 values with the preferred values within the uncertainty. Overall, the method for the in-situ determination of Cu isotopes presented here is a promising tool for research on bronze materials, and QT13 can be considered as a candidate matrix-matched reference material for in-situ Cu isotope determination for bronze artifacts.