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"Tyler B Coplen II, Research Chemist, Reston, VA "< [log in to unmask]> (Tyler Coplen)
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Dear Darren,
First, retroconvertion of PDB and SMOW data to VPDB and VSMOW may not be
possible if isotopic results of reference materials are not available.
Coplen, Normalization of oxygen and hydrogen isotope data, Chemical
Geology (Isotope Geoscience Section), v. 72, p. 293-297, 1988, discusses
the mechanics of converting isotopic data to VPDB and VSMOW and should
be helpful. If you have additional questions, please contact me directly.
An example showing the conversion of measured delta O-18 values to VSMOW
is given by Coplen, Kendall, and Hopple, Comparison of stable isotope
reference samples, Nature, v. 302, p. 236-238, 1983. Note that the values
in column 7 are expressed on a scale such that SLAP is -55.5 per mill
exactly relative to VSMOW and that the value of NBS 19 in this column is
-2.19 per mill. To convert data in this column from PDB to VPDB, one would
adjust the coefficients used to generate column 7 data so that NBS 19
becomes -2.2 per mill exactly instead of -2.19 per mill.
For C-13 data it is only necessary to adjust the isotopic results so that
the delta C-13 of NBS 19 becomes +1.95 per mill. If the value of NBS 19
is not given by authors of an article, you may need to contact the authors
to determine what value they would have reported for their measurement of
NBS 19.
Tyler B. Coplen
U.S. Geological Survey
431 National Center
Reston, VA 20192
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