A redetermination of absolute values for 17RVPDB‐CO2 and 17RVSMOW

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Abstract
In a companion paper in this issue we presented a review of the current state of 17O‐corrections for CO2 mass spectrometry and considered an approach (including algebraic formulae) of how to determine absolute values for 17RVPDB‐CO2 and 17RVSMOW. Here we present the results of experiments conducted to determine these values. Two oxygen gases (one depleted in heavy isotopes and the other isotopically normal oxygen) were analysed to obtain the relative 17O content. Samples of both gases were converted into CO2, and the resulting CO2 samples were analysed as well. Possible experimental and analytical errors are carefully considered and eliminated as far as feasible. Much attention was paid to understanding and dealing with cross‐contamination effects occurring in the mass spectrometer. Based on the data obtained, the absolute values are calculated to be: 17RVPDB‐CO2 = 0.00039511 ± 0.00000094 and 17RVSMOW = 0.00038672 ± 0.00000087 (expanded uncertainties). Both values are on the original scale of Craig (Geochim. Cosmochim. Acta 1957; 12: 133–149) with 13RVPDB‐CO2 = 0.0112372. A 17O‐correction algorithm incorporating the newly determined value for 17RVPDB‐CO2 and λ = 0.528 by Meijer and Li (Isot. Environ. Health Stud. 1998; 34: 349–369) is constructed. A computational test is performed to demonstrate the degree of δ13C bias relative to the previously known correction algorithms. δ13C values produced by the constructed algorithm are in the middle of the values produced by the other algorithms. We refrain, however, from giving any recommendation concerning which 17O‐correction algorithm to use in order to obtain δ13C data in the most accurate way. The present work illuminates the need to reconsider recommendations concerning the correction algorithm. Copyright © 2003 John Wiley & Sons, Ltd.