We have been trying out several variations of the microdiffusion method
for the determination of 15N-labelled ammonium and nitrate in KCl soil
extracts. Most of the methods published (or discussed on Isogeochem) use
either H2SO4, KHSO4 or sometimes boric acid to trap the volatilized
ammonia after addition of MgO (and Devarda's alloy) to the KCl solution.
Using sulphate-based traps we get an accumulation of sulphur oxides
(apparantly SO and SO2) in the elemental analyser - IRMS system (Carlo
Erba coupled to a Finnigan Delta Plus), which are cumbersome to remove
through heating the GC-column (porapak Q) and changing the combustion
and reduction tubes.
I wonder if anyone has tried more instrument-friendly acids, and if so
which would be most suitable?.
A related question is the the type of filter paper disc is most suitable
in this method. Cellulose or glassfibre filter paper?, again having the
longevity of the combustion tubes in mind.

Grateful for any suggestions,

Ernst Witter

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Dr. E. Witter
Department of Soil Sciences
Box 7014
Swedish University of Agricultural Sciences (SLU)
75007 Uppsala
Sweden

Tel +46 18 671237
Fax +46 18 672795
E-mail: [log in to unmask]