The ammonium sulfate suite of standards (and many other NIST and IAEA 
standards) typically aren't used to directly normalize the samples with. While 
these supplies are often scarce, they are used to calibrate house standards 
with, and the house standards are used daily instead. It's a time-consuming 
process to confidently determine the value of a house standard, but somebody 
may have a small amount of an organic sample that they've already determined 
the d15N values of and could send you a small quantity of it if you need 
something to use right away. 
Cheers,
-tom millican


On Friday 11 December 2009 09:03:11 am Heaton, Timothy H E wrote:
> The reference materials for calibrating d15N are inorganic forms of N -
>  especially ammonium sulphate - and therefore likely to react somewhat
>  differently to organic forms of N - e.g. plants etc. - in continuous flow
>  EA-IRMS systems.
> 
> Is there any concensus as to how to deal with this if one wants to properly
>  'calibrate' an organic N material by running it against, e.g. IAEA N-1 &
>  N-2?
> 
> Should one, for example, add N-free sucrose to these IAEA ammonium
>  sulphates to produce a sample matrix more like an organic material?
> 
> Tim H.E. Heaton
> NERC Isotope Geosciences Laboratory
> British Geological Survey
> Keyworth, Nottingham NG12 5GG, England
> (www.bgs.ac.uk/nigl/index.htm)
> Tel. +44(0)115 936 3401
> Email: [log in to unmask]
>