hi Susan,
I saw your query about S linearity.  We have both a Micromass Optima and a
Finnigan Delta Plus XL on which we run S.  The Optima is linear in a rather
small range, about 1-3.5 nA, the trap current is set at 400uA.  I think
this is different than the "recommended" trap current.  I've seen this
setting make a difference for C and N linearity, so maybe that is where
your S linearity problem lies as well...  For the Delta, we haven't run as
much S on this machine but I have had occasional linearity problems, but
this seems to happen when the source gets dirty.  I have compensated by
turning the extraction pot back and retuning everything else.  By trial and
error I've been able to find an extraction setting where the linearity is
decent without compromising the sensitivity.  If the source is dirty this
quick fix doesn't last very long.  So if you have a Finnigan, maybe try
turning the extraction down and retuning.  The linear range for the
Finnigan is better, about 1-4.5V.  We run BaSO4 standards and ZnS
standards.

hope that might help!
Cyndi
__________________________
Cyndi Kester
Ecologist
U.S. Geological Survey
DFC, Building 21, MS 963
Denver, CO 80225

phone: 303-236-0278
fax:    303-236-4930
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