Re-determination of R(13C/12C) for Vienna Peedee belemnite (VPDB).

ABSTRACT

RATIONALE The isotope ratio for the internationally agreed but virtual zero-point of the carbon isotope-delta scale, Vienna Peedee belemnite (VPDB), plays a critical role in linking carbon isotope delta values to the SI. It is also a quantity used for various data processing procedures including '17O correction', clumped isotope analysis and conversion of carbon isotope delta values into other expressions of isotopic composition. A value for RVPDB(13C/12C) with small uncertainty is therefore desirable to facilitate these procedures. METHODS: The value of RVPDB(13C/12C) was determined by errors-in-variables regression of isotope delta values traceable to VPDB measured by isotope ratio mass spectrometry against isotope ratios traceable to the SI by use of gravimetric mixtures of 12C- and 13C-enriched d-glucose measured by multicollector inductively coupled plasma mass spectrometry. RESULTS: A value of RVPDB(13C/12C) = 0.0111105 ± 0.0000042 (expanded uncertainty, k = 2) was obtained. CONCLUSIONS: The new value for RVPDB(13C/12C) agrees very well with the consensus values calculated from previous measurement results proposed by Kaiser and by ourselves, as well as recent determinations independent of mass spectrometry. The expanded uncertainty of 0.4‰ when expressed as an isotope delta value is a tenfold improvement over the previous best measurement of the isotopic composition of carbon.