Hydrogen Isotope Materials
Water was a prime medium of the first studies; thus, isotopic reference materials were first needed for water. Beginning in the 1950s, steam condensate from Potomac river water (NBS 1) and snow melt water from Yellowstone (NBS 1a) were distributed by the NIST for δ2H mass-spectrometric measurements of water. To anchor isotope-ratio results from water samples to the major world water pool, a new (virtual) Standard mean Ocean Water (SMOW) scale was introduced by Craig in 1961.
SMOW was introduced as a concept first, and today a common water standard replaces this virtual scale with a physically existing reference material VSMOW. At the 37th IUPAC General Assembly in 1993 in Lisbon, the Commission recommended that δ2H values of all hydrogen-bearing materials be measured and expressed relative to VSMOW reference water on a scale normalized by assigning consensus values of −428 ‰ to SLAP reference water, and authors should clearly state so in their reports.
|VSMOW||8535||water||0 ‰ *|
|SLAP||8537||water||-428 ‰ *|
|NBS 22||8539||oil||-116.9(8) ‰|
|NBS 30||8538||biotite||-65.7(3) ‰|
|USGS42||human hair (Tibetian)||-78.5(2.3) ‰|
|USGS43||human hair (Indian)||-50.3(2.8) ‰|
* Exact values defining the δ2HVSMOW-SLAP scale. Note that both scale-defining materials, VSMOW for the scale origin and SLAP for the scale span, are given without uncertainty. These are fixed consensus values and they cannot be changed without changing the scale as well.
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.