At 15:38 25.01.99 +0100, you wrote:
>Dear listmembers
>
>I am looking for the d13C value of NBS21, a graphite standard now
>replaced by USGS-24 in recent compilations of standard references. I
>would be grateful to anyone who can provide me some data or
>bibliographic references.
>
>Christine FLEHOC
>BRGM - SMN/ANA/ISO
>3 Ave C. Guillemin
>B.P. 6009
>45060 ORLEANS cedex 2 FRANCE
>fax 33 02 38 64 37 11
>e-mail [log in to unmask]
>

Christine,

Coplen et al., Comparison of stable istope reference samples, Nature 302:
236-238 (1983) have reported a value of -(28.13+-0.03) permil vs PDB (n=4)
for delta 13C of NBS21. We measured the delta 13C of the same graphite
standard several times over more than ten years and found the following
values: -(28.15+-0.007) (n=15) (Leuenberger, 1986); -(28.18+-0.03) (n=3)
(Saurer, 1989); -(28.244+-0.031) (n=4) (Borella,  1998).

Gonfiantini et al., Standards and intercomparison materials distributed by
the international atomic energy agency for stable isotope measurementss, in
Reference and intercomparison materials for stable isotopes of light
elements, edited by IAEA:13-29 (1993) reported a value of -(15.994+-0.105)
permil vs PDB for delta 13C of USGS24 (n=8). We also measured this graphite
and found a value of : -(16.016+-0.024) (n=3) (Borella, 1998).

I also would be pleased to know about further references.

Best wishes,

Silvio




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