Development of a New Certified Copper Isotopic Reference Material (GBW04624) and its Application to Copper Isotope Measurements in Geological Samples

To meet the demand of reliable copper isotopic data in various scientific research, a new copper isotopic reference material GBW04624 with high purity (99.9996%), sufficient homogeneity and stability was developed in this study. A copper isotope amount ratio of n(⁶⁵Cu)/n(⁶³Cu) = 0.44559 ± 0.00018 (U, k = 2) in GBW04624 was obtained by calibrated mass spectrometry involving two mass bias correction strategies. The uncertainty of property values was evaluated and traceability to the International System of Units (SI) was established. Copper isotope ratios in geological reference materials GBW07105 and BCR-2 were determined relative to both GBW04624 and the internationally recognised copper isotopic reference material NIST SRM 976. The conversion between δ⁶⁵Cu values relative to NIST SRM 976 and GBW04624 was achieved by applying a δ⁶⁵Cu_{GBW04624–NIST SRM 976} value of 0.252 ± 0.015‰ (U, k = 2).