EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The IAEA carbonate reference materials aimed at the VPDB scale realization with low uncertainty.

Sergey Assonov, Ales Fajgelj, and Manfred Gröning
Sergey Assonov et al.
  • IAEA, Terrestrial Environment Laboratory, Vienna, Austria (

The stable isotope scales of the light elements (H, C, O, S) are artefact-based (related to a primary reference material) and their practical realisation is based on several refence materials (RMs) traceable to the primary RM on a respective delta-scale. NBS19 carbonate, the primary RM for the VPDB scale introduced in 1987, exhausted in 2012, and its replacement was not available for several years. In 2016, IAEA-603 carbonate (replacement for NBS19) was released as the new primary RM having been carefully calibrated versus the remaining NBS19. The IAEA-603 uncertainty in δ13C and δ18O for the first batch (5200 ampoules produced) is ±0.010 ‰ and ±0.040 ‰ respectively (1-sigma level); the homogeneity assessment is the major component of total uncertainty which is limited by the best mass-spectrometer performance and the method (carbonate-acid reaction) reproducibility.

In 2015, monitoring of LSVEC (formerly the second scale-anchor on the VPDB scale) detected variable drifts in its δ13C value and therefore the use of LSVEC as RM for δ13C was discontinued. It was recognised that a replacement for LSVEC is needed for normalization of the δ13C measurement results, also to address the strict uncertainty requirements for δ13C observations in atmospheric CO2 and methane (≤0.01 ‰ and ≤0.02 ‰ correspondingly). Similar to IAEA-603, any new RMs will address the technical requirements for RMs laid out by ISO Guide 35: 2017 including (i) RM batch production and batch characterisation; (ii) homogeneity and stability assessment of the final product (RMs sealed off in 0.5 g ampoules) and (iii) value and uncertainty assignment based on the metrological traceability. Three new carbonate RMs are in preparation at the IAEA; the uncertainty in δ13C for all three materials due to RM’ homogeneity is already confirmed at ≤0.01 ‰ (on 10 mg aliquots), which is at the limit of the best modern mass-spectrometers. The isotopic characterisation of these new carbonate RMs is in progress; they should be released in 2020.

Together with IAEA-603, the three new RMs will provide a reliable realization of the VPDB scale with the lowest possible uncertainty. With these RMs users can (i) select RMs in a suitable δ13C range, (ii) detect any potential drift of RMs including the behaviour of daily lab-standards and (iii) detect any potential problem in applying the 17O correction at end-user laboratories. In conclusion, these new reference materials will allow laboratories worldwide to establish metrological comparability for decades.

How to cite: Assonov, S., Fajgelj, A., and Gröning, M.: The IAEA carbonate reference materials aimed at the VPDB scale realization with low uncertainty. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11525,, 2020

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