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 δ37Cl signatures in natural samples.
Industrially produced organic chlorine compounds exhibit almost an order of magnitude wider range of δ37Cl 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.
|NIST SRM 975||NaCl||+0.43 ‰ *|
|NIST SRM 975a||NaCl||+0.2 ‰ **|
* Exact value defining the δ37ClSMOC 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.