Dear Anita,

One amino acid (phenylalanine) may not be enough.  The 15N value of an AA depends on the substrate it it was synthesized from.  Note that Wolfram's USGS40 and USGS41 are both glutamate with d15N values of -4.52 and +45.57 per mil.

You can find lots of information on natural abundance of amino acids in papers by Fogel, Hare, Tuross, Engel, Macko and others.

A suite of AAs with different C&N compositions is very good for monitoring EA performance. I recommend buying several AAs with different formula weights and C:N ratios for internal references and QC.

Best
Stan


Thank you all for your suggestions, both on the list as directly to me. It is a good idea to calibrate our organic working standard (labstandard) against organic reference standards like USGS 40 and USGS 41, instead of the inorganic ones from the IAEA (N1 and N2).
So the easiest thing to try is to buy phenylalanine in a large quantity and to order the USGS 40 and 41.
I couldn't find the natural range in nitrogen 15 of all the amino acids. If someone knows if there is a better choice then phenylalanine, please let me know.
Thanks again, it was very helpful,
--

Anita Aerts-Bijma
Centre for Isotope Research, University of Groningen.

Centrum voor IsotopenOnderzoek (CIO), Rijksuniversiteit Groningen
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tel +31-50-3634716 fax +31-50-3634738
http://www.rug.nl/cio


-- 
Stanley H. Ambrose, Professor
 
Department of Anthropology
Environmental Isotope Paleobiogeochemistry Laboratory
Center for African Studies
Nutritional Sciences Interdisciplinary Graduate Program
Program in Ecology, Evolution and Conservation Biology
Department of Geology

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