Peter,

Rapid Commun. Mass Spectrom. 14, 1266-1268 (2000) describes a modified
ion-exchange extraction of NO3 coupled with details of on-line 15N analysis
of the AgNO3 product.  On-line 18O-NO3 has been limited by the costs of
getting a CO reference gas that's not relatively depleted to the U.S. (see
discussions on this topic in Isogeochem's archive earlier this year).

A fairly complete list of references is in the paper above.  They cover
other types of extractions, off-line analyses, and CO2 conversion
possibilities.

Cheers,

-------------------------------------------------
Robert D. Stickrod II
Idaho Stable Isotopes Laboratory
Department of Forest Resources
College of Natural Resources, 214
P.O. Box 441133, University of Idaho
Moscow, ID 83844-1133, U.S.A.
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lab: (208) 885-6512
fax: (208) 885-6226
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