Dear List;

Just to add to the debate about the micro diffusion method. We have been
using it to look at soil extracts and leachates for several years now and
have had no problems. Even at natural abundance levels we can get good
results. We find that contamination from the reagents used is more of a
problem than isotope discrimination during diffusion, particularly KCl and
Devarda's alloy which can contain quite high N levels.

We always use KHSO4 and have noticed sulphur residue in the liner of the
oxidation tube. This seems to have no effect on the oxidation and reduction
columns or the GC column, although occasionally we do see a reduced lifetime
of the oxidation column. We run a Europa Scientific Roboprep coupled to a
20-20 Mass Spec. We prefer to use Glass Fibre discs (GF/D) and if used in
conjunction with the easily replaceable oxidation column liners we have no
problems regarding removal of the glass residue in the oxidation column.

Jon Fear....
Senior Laboratory Technician
Department of Agricultural Sciences
Imperial College at Wye
Wye
Ashford
Kent TN25 5AH.

Tel:020 759 42879
Fax: 020 759 42640
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