Rebecca,

we set up a high-temperature on-line pyrolysis technique to be able to
determine del 18O of organic as well as inorganic samples. I tried silver
and potassium nitrate standards, both work fine, and even the del 15N value
of nitrates could be measured with this set-up. So I guess this is the
easiest and fasted method around, but care has to be taken with real
samples, becauce with this technique, you convert all oxygen in your sample
to CO. Obviously you can expect problems when samples are not as pure as
they should be and contain other oxygen sources than only nitrate.
You find a description of our method in Kornexl et al., Rapid Commun Mass
Spectrom, 13 (1999), issue 16, pp 1685-1693.

Hope this helps

Barbara
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Dr. Barbara E. Kornexl
UFZ - Umweltforschungzentrum Leipzig-Halle GmbH
Sektion Analytik
Permoserstr. 15
D-04318 Leipzig

Tel.:   ++49/341/235-   2252
Fax:                    2625
E-Mail: [log in to unmask]
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