Determination of the isotopic composition of copper in a certified reference material HICU-1 by MC-ICP-MS using gravimetric isotope mixture calibration

Abstract

Isotopic analysis by mass spectrometry relies on certified reference materials (CRMs) in order to correct instrumental isotopic fractionation (aka mass bias). Currently, SRM976 copper isotopic standard from the National Institute of Standards and Technology (NIST) remains the sole internationally recognized reference material for copper isotope ratio. However, the SRM976 material is no longer available and new copper isotopic CRMs are needed to serve as reference points for decades to come. In this study, we report an independent and fully calibrated isotope ratio measurement of a high-purity copper certified reference material, HICU-1, at the National Research Council Canada (NRC). MC-ICP-MS was employed for the isotope ratio measurements which were calibrated using the gravimetric isotope mixture approach involving two near-pure enriched copper isotopes. Copper isotope ratio n(⁶³Cu)/n(⁶⁵Cu) = 2.2413 ± 0.0009 (95% CI, k = 2) was established in the NRC HICU-1 and its isotopic composition has been shown to be nearly identical to that of NIST SRM976.