Good Morning Everybody,
We're struggling to get good precision with
our GV Isoprime/Dual Inlet. We are running 100ug carbonate
samples/standards. We've achieved the specified +/-0.05 d18O (1 sd) on
some runs, but it doesn't last. Our last 4 runs resulted in +/- 0.07,
0.12, 0.22, 0.09 d18O (1 sd).
The mass spec seems to be working beautifully as
indicated by the peak shape, all open analysis, and single cold finger
volume anlaysis with ref gas on both sides of the dual inlet.
We learned some techiques from our esteemed
and helpful GV service engineers regarding the carbonate prep line. These
include replacing the prep line and heating the prep line between runs. We
saw improvements in performance, especially after heating the line.
Unfortunately, the good data quality deteriorates quickly (several runs).
We've experimented with heating the prep line continuously, heating between
samples, and not heating at all. Our latest experiments involve
replacing the 1/16" ss prep line with fat tubing (1/4" convoluted ss
tubing). The fat tubing showed promising results at first, but alas, has
deteriorated again (above data collected with fat tubing).
I like the rapid pumpdown and definitive leak
checking that the fat tubing allows. My thought was that the
increased conductance and lower surface area to volume ratio of the fat tubing
would be a great benefit.
When using 1/16" tubing, it
is standard 316 ss tubing that is cut with a dremel
Any ideas or suggestions for further testing would
be greatly appreciated.
ICPMS Lab Manager
Department of Geological Sciences, Marine
Unviversity of California Santa Barbara
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