Oxygen Isotopic Reference

 δ¹⁸O Values of Oxygen Isotopic Reference Materials

*  Exact values defining the delta scale
** Isotope amount ratio

Recommendation on the Reporting of δ¹⁸O Measurements

At the 37th IUPAC General Assembly in 1993 in Lisbon, the Commission recommended guidelines for δ¹⁸O measurements.

Water
Relative n(¹⁸O)/n(¹⁶O) values (δ¹⁸O) of water should be expressed relative to VSMOW water (0 ‰) on a scale normalized such that the δ¹⁸O of SLAP water is –55.5 ‰ exactly and so stated in author’s report.

Carbonate
Relative n(¹⁸O)/n(¹⁶O) values ( δ¹⁸O) of carbonate should be expressed on a scale normalized such that the δ¹⁸O of SLAP reference water is –55.5 ‰ exactly relative to VSMOW water, and so stated in author’s report.  The measured value should be expressed either

• relative to VPDB on a scale such that the δ¹⁸O of NBS 19 calcite is –2.2 ‰ exactly, stating the value of the oxygen isotopic fractionation factor used to calculate the δ¹⁸O of the carbonate sample and NBS 19 if they are not identical, or
• relative to VSMOW water (0 ‰), stating the values of all isotopic fractionation factors upon which the δ¹⁸O measurement depends.

If the δ¹⁸O values cannot be reported on a normalized scale (perhaps because of the lack of a capability to analyze water samples), the author’s measured δ¹⁸O of NBS 18 carbonatite or other internationally distributed isotopic reference material should be reported, as appropriate, had it been analyzed with the samples.

Other Substances (Oxygen Gas, Sulfate, Silicate, Phosphate, etc.)
Relative n(¹⁸O)/n(¹⁶O) values ( δ¹⁸O) of all other oxygen-bearing substances should be expressed relative to VSMOW water (0 ‰) on a scale normalized such that the δ¹⁸O of SLAP water is  –55.5 ‰ exactly relative to VSMOW water, and so stated in author’s report, stating either

• the values of all isotopic fractionation factors upon which a δ¹⁸O values depends, or
• the author’s measured δ¹⁸O of NBS 28 quartz, NBS 127 barium sulfate, USGS35 sodium nitrate, or other internationally distributed reference material had it been analyzed with the samples.

If the δ¹⁸O values cannot be reported on a normalized scale (perhaps because of the lack of a capability to analyze water samples), the author’s measured δ¹⁸O of NBS 18 carbonatite or other internationally distributed isotopic reference material should be reported, as appropriate, had it been analyzed with the samples.

Authors should discontinue reporting their δ¹⁸O values relative to SMOW and PDB. 

The full recommendation appears in:
Reporting of stable hydrogen, carbon, and oxygen isotopic abundances, Coplen, T. B., Pure Appl. Chem., 66, 273-276 (1994).  [full text - pdf 242 KB] {H, C, O Isotopic Rept Guidelines.pdf}

References

1. Gonfiantini, R., Standards for stable isotope measurements in natural compounds, Nature, 271, 534-536 (1978).
2. Gonfiantini, R., Stichler, W., and Rozanski, K., Standards and intercomparison materials distributed by the International Atomic Energy Agency for stable isotope measurements, in Reference and intercomparison materials for stable isotopes of light elements, Vienna, Austria, International Atomic Energy Agency, IAEA-TECDOC-825, 13-29 (1995).
6. Coplen, T. B., Kendall, C., and Hopple, J., Intercomparison of stable isotope reference samples, Nature, 302, 236-238 (1983).
8. Böhlke, J. K., Mroczkowski, S. J., and Coplen, T. B., Oxygen isotopes in nitrate: new reference materials for ¹⁸O:¹⁷O:¹⁶O measurements and observations on nitrate-water equilibration, Rapid Comm. Mass Spectrom., 17, 1835-1846 (2003).
12. Coplen, T.B., Hopple, J.A., Böhlke, J.K., Peiser, H.S., Rieder, S.E., Krouse, H.R., Rosman, K.J.R., Ding, T., Vocke, Jr., R.D., Révész, K.M., Lamberty, A., Taylor, P., and De Bièvre, P., Compilation of minimum and maximum isotope ratios of selected elements in naturally occurring terrestrial materials and reagents, U.S. Geological Survey Water-Resources Investigations Report 01-4222, 98 p (2001).
14. Verkouteren, R. M.; Klinedinst, D.B., Value Assignment and Uncertainty Estimation of Selected Light Stable Isotope Reference Materials:  RMs 8543-8545, RMs 8562-8564, and RM 8566, NIST Special Publication 260-149, National Institute of Standards and Technology, Gaithersburg, Maryland (2004).
15. Calculated from data in ref (14) and the relation between VPDB and VSMOW given on page 36 of reference (12).
29. Brand, W. A., Coplen, T. B., Aerts-Bijma, A. T., Böhlke, J. K., Gehre, M., Geilmann, H., Gröning, M., Jansen, H. G., Meijer, H. A. J., Mroczkowski, S. J., Qi, H., Soergel, K., Stuart-Williams, H., Weise, S. M., and Werner, R. A., Comprehensive inter-laboratory calibration of reference materials for δ18O versus VSMOW using various on-line high-temperature conversion techniques, Rapid Comm. Mass Spectrom., 23, 999-1019 (2009).
30. Calculated from data in ref (8) and reference (29).
32. Coplen, T. B., and Qi, H., USGS42 and USGS43: Human-hair stable hydrogen and oxygen isotopic reference materials and analytical methods for forensic science and implications for published measurement results, Forensic Sci. Int. (2011), doi:10.1016/j.forsciint.2011.07.035