Stable Isotope Geochemistry


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[log in to unmask] (Dan Bryant)
Tue, 7 Jan 1997 07:59:11 -0400
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For phosphate d18O, most labs use NIST SRM-120c, which is prepared from a
Miocene marine carbonate fluorapatite and has a d18O of about +21 SMOW.
SRM-120c and it's cousin, SRM-694 (also CARFAP, about +13 SMOW if I
remember correctly) are offered as trace/minor/major element standards and
not as isotope standards, although we have found no measureable isotopic
differences among bottles (+/- 0.1 to 0.3 per mil by Ag3PO4 fluorination).
There is no widely-distributed carbonate hydroxylapatite standard. However,
for most analytical methods (including the old BiPO4 method) which have
complete dissolution of the apatite, the choice between a fluorapatite and
a hydroxylapatite should not matter as there is quantitative dissolution
and re-precipitation of the phosphate anion.

Kolodny and Luz, and much of the literature from 5 or more years ago, used
either NIST SRM-120b (now exhausted and replaced by 120c) or an internal
KH2PO4 reagent. Just recently NIST has offered "bone ash" and "bone meal"
standards for trace element work, but I do not know if anyone has used
these as a d18O standard. Jim O'Neil was distributing a set of standards
with different d18O compositions. Perhaps his are hydroxylapatite, but I do
not know.

Good luck,

Dan Bryant
E-mail: [log in to unmask]
Home page:
Tel. (609) 258-2612; Fax (609) 258-1274
Department of Geoscience
Princeton University
Princeton, NJ 08544