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    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:

    δVPDB(18O, X) = 0.97001×δVSMOW(18O, X) − 29.99 ‰

    δ(18/16O) Values of Reference Materials

    Name NIST RM Material δVSMOW(18O)
    VSMOW8535water 0 ‰ *
    SLAP8537water-55.5 ‰ *
    NBS 198544limestone+28.65 ‰
    NBS 188543carbonatite+7.20(3) ‰
    Air-O2air+23.88(2) ‰
    SMOWn/a 0 ‰
    VSMOW2water 0.00(2) ‰
    SLAP2water-55.50(2) ‰
    GISP8536water-24.78(8) ‰
    GISP2water-33.43(2) ‰
    NBS 1water-7.91(4) ‰
    NBS 1awater-24.36(3) ‰
    USGS45water-2.24(1) ‰
    USGS46water-29.80(2) ‰
    USGS47water-19.80(2) ‰
    USGS48water-2.22(1) ‰
    IAEA-304Awater[249.2, 254.2] ‰
    IAEA-304Bwater[498.9, 506.1] ‰
    IRMM BCR-658water-ethanol-7.19(4) ‰
    IRMM BCR-659water-ethanol-7.18(2) ‰
    NBS 20Solnhofen limestone+26.64(2) ‰
    LSVEC8545Li2CO3+3.69 ‰ **
    IAEA-CO-9BaCO3+15.04 ‰
    NBS 288546silica sand (optical)ca. +9.6 ‰ **
    NBS 308538biotiteca. +5.2 ‰ **
    NBS 1278557BaSO4+8.59(26) ‰
    IAEA-SO-5BaSO4+12.13(33) ‰
    IAEA-SO-6BaSO4-11.35(31) ‰
    OGSBaSO4+9.31(6) ‰
    CO2-Heavy8562CO2+11.86 ‰
    CO2-Light8563CO2-3.64 ‰
    CO2-Biogenic8564CO2+20.52 ‰
    USGS328558KNO3+25.4(2) ‰
    USGS348568KNO3-27.78(37) ‰
    USGS358569NaNO3+56.81(31) ‰
    IAEA-NO-38549KNO3+25.32(29) ‰
    IAEA-600caffeine-3.48(53) ‰
    IAEA-601benzoic acid+23.14(19) ‰
    IAEA-602benzoic acid+71.28(36) ‰
    USGS42human hair+8.56(10) ‰
    USGS43human hair+14.11(10) ‰
    Name NIST RM Material δVSMOW(18O)

    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.


    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).