Anita and others,
Apparently the supplier does matter as evidenced below by an off-line e-mail
that I received. I purchased my Caffeine from Fisher Scientific (more than many
life-times supply!) and get approx dC13 approx -42 per mil.
Charlotte Lehmann

"Hello Charlotte,
We also use caffeine as one of the standards for normalization of both C13 and
N15.  However the Caffeine we use is from Sigma Aldrich grade ultra pure, and
it gives us -29.98 +/- 0.2 per mil C13.  If possible I would like to know the
source of caffeine you use since some of  samples I have to run is around -35
per mil and a standard with lower C13 would certainly help in reporting the
data.  Thank you.
Regards,
Shapna

Shapna Mazumder

Environmental Management of Drinking Water
Dept. of Biology, University of Victoria
Victoria, B.C., Canada
(250)-721-6150
[log in to unmask]


www.uvic.ca/water"

Quoting Anita Aerts-Bijma <[log in to unmask]>:

> Thank you for your reply to my e-mail request.
> We have an EA-CF-IRMS combination. This system is calibrated with
> primary standards from the IAEA and the NIST. However, we only get a
> small quantity of these, so besides these primary standards we want
> to use other standards in every batch. This way we would have another
> check on our results. Do you have any suggestions as to which
> material (in a large quantity) with a very negative deltaC13 we could
> use. Preferably a solid material which can be combusted in the same
> batch as the samples. I received one suggestion to use caffeine. Does
> this material always have a negative deltaC13, or does this depend on
> the supplier. Has any of you experience with that?
>
> Thanks, and regards,
>
> Anita Aerts-Bijma
> Centrum voor IsotopenOnderzoek (CIO), Rijksuniversiteit Groningen
> Nijenborgh 4, 9747 AG  Groningen, Netherlands
> tel:050-3634716


Charlotte Lehmann
Research Technician
Department of Geology
Bates College
Lewiston, ME 04240
207-786-6485