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    Chlorine Isotope Materials

    Most chlorine is in the world oceans, where the isotopic signature does not change by much more than 1 ‰. Hence, high precision is a requirement for studying δ(37Cl) signatures in natural samples. Industrially produced organic chlorine compounds exhibit almost an order of magnitude wider range of δ(37Cl) values.
    Before approximately 2002, most delta measurements of chlorine isotopes were expressed relative to seawater chloride (SMOC for Standard Mean ocean Chloride), which was thought to be homogeneous in chlorine isotopic composition to within approx. 0.15 ‰. Today, NIST SRM 975 has been internationally accepted as the new anchor for the SMOC scale.

    δ(37Cl) Values of Reference Materials

    Name Material δSMOC(37Cl)
    SMOCn/a 0 ‰
    NIST SRM 975NaCl+0.43 ‰ *
    NIST SRM 975aNaCl+0.2 ‰ **
    ISL-354NaCl+0.05(2) ‰
    Name Material δSMOC(37Cl)

    Footnotes      Back to Top
    * Exact value defining the δ(37Cl) SMOC 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)