Carbon Isotope Materials

The n(¹³C)/n(¹²C) ratio probably is the most frequently analyzed stable isotope quantity. A variability in carbon isotopic compositions of about 180 ‰ is observed in naturally occurring terrestrial materials.

δ(¹³C) Values of Reference Materials

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* Exact values defining the δ(¹³C) VPDB scale.
** See the Assessment of international reference materials for isotope-ratio analysis for more details.
Values in parenthesis are expanded (k = 2) uncertainties applicable to the last digits. The values listed in this table are compilation and are not necessarily CIAAW recommendations.

Citation

W.A. Brand et al
Assessment of international reference materials for isotope-ratio analysis Pure and Applied Chemistry 86, 425-467 (2014)

In 2017, the CIAAW noted that the international isotopic reference material LSVEC lithium carbonate which (together with NBS 19) is used to realize the carbon isotope delta scale (VPDB), is able to absorb carbon dioxide from air. This process changes the carbon isotope ratio in LSVEC with time. Given that LSVEC is unsuitable as a reference material for carbon isotope ratio analysis, its use is no longer recommended. Carbon isotope delta measurements must still be normalized to the VPDB scale using at least two suitable international reference materials selected by the users as appropriate (see the IUPAC Press Release).

From 2005-2017, the CIAAW recommended that δ(¹³C) values of all carbon-bearing materials be measured and expressed relative to the VPDB on a scale normalized by assigning consensus values of –46.6 ‰ to LSVEC lithium carbonate and +1.95 ‰ to NBS 19 calcium carbonate (see Atomic weights of the elements 2005).