Isotopers,

We have had some experience running natural abundance and labeled samples
in our CE2500 and Delta + XLS system.

Willi Brand is correct, you do not need two CF-IRMS's, the "memory is in
the EA.  If you have the halogen lights on in the source of the Delta, the
source stays clean.  After running the labeled N-15 samples our 30
backgrounds were through the roof.  To get them back down again we had to
change out the entire insides of the EA including the combustion and
reduction tubes, water trap, and the GC column.  We have one GC column for
labeled samples and one for natural abundance, but we don't run labeled
samples anymore for other reasons, software.

The real problem with the labeled samples was that the Isodat software
seemed to have errors in calculating the Atom %N.  We ran the same samples
on a VG system at LLL that was "optimized" for labeled samples and got
different Atom %N results.  The F MAT software seems to calculate too high
a value compared to the Livermore results.  But then there are several
problems with the Isodat software including the blank correction, which
seems to work sometime and other times goes Viking.  We wind up doing all
the corrections by hand offline.  Can anyone explain these types of
software calculation problems?

Bill
----------------------------------------------------------
Dr. William J. Showers
Professor
Director, Stable Isotope Lab
Director, RiverNet Program

Dept. of Marine, Earth, & Atm Sciences
1125 Jordan Hall
North Carolina State University
Raleigh, NC 27695-8208

(919) 515-7143 - voice
(919) 915-1498 - cell
(919) 515-7802 - fax
[log in to unmask] - email

     Even if you are on the right track, you'll get run over if you just
sit there.