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,
Centre for Isotope Research, University of Groningen.
Centrum voor IsotopenOnderzoek (CIO), Rijksuniversiteit Groningen
Nijenborgh 4, 9747 AG Groningen, Netherlands
tel +31-50-3634716 fax +31-50-3634738