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After two decades a second anchor for the VPDB δ13C scale


Brand,  W. A.
Service Facility Stable Isotope/Gas Analytics, Dr. W. A. Brand, Max Planck Institute for Biogeochemistry, Max Planck Society;

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Coplen, T. B., Brand, W. A., Gehre, M., Gröning, M., Meijer, H. A. J., Toman, B., et al. (2006). After two decades a second anchor for the VPDB δ13C scale. Rapid Communications in Mass Spectrometry, 20(21), 3165-3166.

In 1985, the primary recommendation of a Consultants' Group Meeting of the International Atomic Energy Agency (IAEA)1 was that a new (Vienna Peedee Belemnite) VPDB δ13C scale be established with NBS 19 carbonate assigned to be +1.95‰ as its single anchor. This recommendation improved δ13C measurement uncertainties,2 especially those of materials with δ13C values near 0‰. A fundamental problem remained that materials with δ13C values far from 0‰, such as NBS 22 oil, had much poorer uncertainties.2, 3 Recognizing that two-point calibrations of the δ2H and δ18O scales substantially improved the agreement among laboratories,4 the IAEA convened a panel in 2004 to review stable carbon isotopic reference materials and to recommend a second reference material for two-point normalization of the δ13C scale. Four laboratories (Centrum voor Isotopen Onderzoek, Groningen, The Netherlands; Max-Planck-Institute for Biogeochemistry, Jena, Germany; UFZ Leipzig-Halle, Leipzig, Germany; US Geological Survey, Reston, VA, USA) performed analytical measurements. Participants at the US National Institute of Science and Technology (NIST) headed the task to estimate consensus means and uncertainties using multivariate Bayesian techniques. Collectively, the laboratories performed 1055 state-of-the-art continuous-flow elemental-analyzer mass spectrometry measurements using the general method of Qi et al.5 on selected organic and inorganic carbon isotopic reference materials. Aims of the work included determining consensus δ13C values of stable carbon isotopic reference materials and confirming that isotopic materials measured in this study are isotopically homogeneous in amounts used in continuous-flow methods [m(C) of approximately ∼40 µg]. Based on high precision mass spectrometric measurements,6, 7 a consensus value of −46.6‰ was assigned to L-SVEC lithium carbonate.8 The results (Table 1) were provided to the International Union of Pure and Applied Chemistry (IUPAC).