Bill,
          This is interesting!  When I carried out an Inter-lab comparison
exercise earlier this year (subscribers may recall my asking for volunteers)
the one outstanding result was the total lack of agreement on 15-N values
for the KNO3 I sent out. This ties in with my experience here using a
Europa roboprep/tracermass system where I get a different result for this
material every time I run it. Again, other materials (Ammonium sulphate,
Acetanilide etc) pose no problems.  I shall try the sugar idea.


       Darren Sleep
       ITE Merlewood
       Grange-over-Sands
       Cumbria  UK