Towards compatibility of stable isotope datasets: Progress with new reference materials and related concepts.

Commonly, datasets obtained in different laboratories and in different years have to be compared /combined. Despite reliable IRMS systems, quality of measurement results cannot be better than quality of Reference Materials (RMs) in use. Thus, to achieve the required data quality and compatibility, one must understand major aspects of RMs and associated concepts.

One of focuses in recent years has been on the δ13C scale. First, the primary RM NBS19 expired in 2009, and its replacement needed to be characterized. Next, the scale-anchor, RM LSVEC, was found to have a significant drift in δ13C of up to 0.35 ‰, so this RM was withdrawn from the use. Reconstruction of its "original" δ13C based on available RMs or other information was not possible. As a result, new scale-anchor RMs had been developed and their value assignment principles revised. Furthermore, one has also demonstrated a compatibility in δ13C obtained for NIST RMs 8562-8564 in 2003-04, 2007 (pre-LSVEC era) and 2020.

Details of developments of new RMs for δ13C and their value assignment provide an example of modern approaches and quality assurance. Although the high accuracy in δ13C obtained for new RMs (±0.010 to ±0.15‰, k=1) may not be necessary in many applications, these principles can be applied to achieve data compatibility in other studies.

Presentation will also discuss isotope scales, their relationships, data treatment, and a simplified scheme of uncertainty propagation. All that is relevant to the use of RMs and quality control materials.