On the subject of ammonium extraction:

We recently submitted a paper to Analytical Chemstry describing a
fairly simple method to collect freshwater ammonium for N-isotope
analysis (Lehmann et al.: A simple method for the extraction of
ammonium from freshwaters for nitrogen isotope analysis). It involves
the adsorption of NH4 on a N-free cation resin and subsequent direct
combustion of the loaded resin. As long as concentration of other
cations are not too high the method worked fine even at relatively
low ammonium concentration (20uM).As Cecily pointed out, DOM can be
reasonably well removed by ion exchange prior to ammonium extraction.
We used an anion resin in the hydroxyl form. In our experiments with
dissolved yeast extract it worked fine.


Moritz
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Moritz Lehmann
Institute of Geology
Swiss Federal Institute of Technology (ETH)
Sonneggstrasse 5
CH-8092 Zürich
Tel.: +41-1-632 36 91
Fax.: +41-1-632 10 80            e-mail: [log in to unmask]
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