Oxygen Isotope Materials

The choice of an oxygen-isotope delta scale depends on the substances measured. Three concurrent delta scales are in use: one for water (VSMOW), one for carbonates (VPDB), and one for oxygen gas (Air-O2). The relations of the scales are well-established; however, they are not fixed permanently. Rather, with new studies or technological advances, these relations might be refined in the future. Nevertheless, the VSMOW and VPDB scales commonly are related for sample X by the equation:

δ_VPDB(¹⁸O, X) = 0.97001×δ_VSMOW(¹⁸O, X) − 29.99 ‰

δ(^18/16O) Values of Reference Materials

Footnotes      Back to Top
* Exact values defining the δ(¹⁸O) VSMOW 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)

At the 37th IUPAC General Assembly in Lisbon (1993), the Commission recommended guidelines for reporting δ(¹⁸O) measurements. The full recommendation appears in Reporting of stable hydrogen, carbon, and oxygen isotopic abundances by T.B. Coplen, Pure Appl. Chem. 66 273-276 (1994).