Final report of CCQM-P204, comparison on CO 2 isotope ratios in pure CO 2

• Published in: Metrologia 2023-11, Vol.60 (1A), p.8026
• Main Authors: Viallon, J, Choteau, T, Flores, E, Idrees, F, Moussay, P, Wielgosz, R I, Loh, Z, Allison, C, Huang, L, Chivelscu, A, Camin, F, Krajnc, B, Ogrinc, N, Fioravante, A de Lima, Fasciotti, M, Monteiro, T V C, Garrido, B C, Rego, E C P, Wollinger, W, Augusto, C R, Michel, S, Lee, J S, Lim, J K, Daëron, M, Kassi, S, Moossen, H, Hai, L, Zhou, Z, Srivastava, A, Shimosaka, T, Webber, E Mussel, Hill−Pearce, R, Brewer, P, Chartrand, M, Rienitz, O, Ebert, V, Flierl, L, Braden-Behrens, J, Nwaboh, J, Emad, A, Simsek, A, Chubchenko, I
• Format: Article
• Language: English
• Subjects: Continental interfaces, environment; Ocean, Atmosphere; Sciences of the Universe
• ISSN: 0026-1394; 1681-7575
• DOI: 10.1088/0026-1394/60/1A/08026

The pilot study CCQM-P204 was aimed at evaluating the level of compatibility of laboratories' measurement capabilities to value assign isotope ratios in samples of pure CO 2 gas, expressed as isotope delta values relative to the relevant international scale: δ 13 C VPDB and δ 18 O VPDB-CO2 . Pure CO 2 gas samples were prepared by the BIPM in batches of 10 samples of the same gas and circulated to participants for measurement. Each participant received four samples of CO 2 with a different nominal δ 13 C VPDB value: −1 ‰; −9 ‰; −35 ‰; and −42 ‰. The BIPM was also responsible for evaluating the homogeneity and stability of the samples. The co-coordinator IAEA received one sample per batch to confirm the batch-to-batch homogeneity. Within-batch and between-batch inhomogeneity was assessed and found to be negligible in comparison to the spread of results reported by participants. Participants used the analytical technique of their choice to measure the isotope delta values. They were requested to report the measurement results together with detailed information on their traceability, measurement methods and data treatment. Results of the comparison were to be compiled by the BIPM and evaluated jointly by the BIPM and the IAEA. The majority of participants reported results using DI-IRMS, and those that reported results based on laser spectroscopy techniques showed a very similar dispersion of results as for DI-IRMS, although generally with greater uncertainty. A total of nineteen participants reported their measurements, with two of them reporting results with different reference materials to provide more insight into the traceability of the measurements. The results were reported with traceability to three different VPDB scale realizations, notably VPDB, VPDB-LSVEC and VPDB2020, with 8, 7 and 6 results reported respectively for each of these. Participants agreed that results based on VPDB and VPDB2020 scale realizations should, in principle, lead to consistent results, whereas those based on VPDB-LSVEC should show a bias that increased as samples became more depleted in 13 C, with the bias approaching 0.2 ‰ for the most depleted sample. This bias was demonstrated by the participant reporting the most precise measurements based on the VPDB-LSVEC realizations, whereas for 2 participants using VPDB-LSVEC scale realizations other issues dominated the consistency of their results. The 3 laboratories using the NIST (8562,8563, 8564) reference materials (reported as