George,
What carbonate standard are you using? We get different results with
different standards, are you sure your standard is homogeneous?
Bill
At 12:47 PM 6/8/2005, you wrote:
>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 tool.
>
>Any ideas or suggestions for further testing would be greatly appreciated.
>
>Take care,
>Georges
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Georges L. Paradis
>ICPMS Lab Manager
>Department of Geological Sciences, Marine Science Institute
>Unviversity of California Santa Barbara
>Santa Barbara, CA 93106
>805-893-7182
><mailto:[log in to unmask]>[log in to unmask]
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
William J. Showers
Dept of Marine, Earth & Atm Sciences
Box 8208
North Carolina State University
Raleigh NC 27695
For express mail: 1125 Faucette Dr.
(919) 515 - 7143 Office
(919) 515 - 7802 Fax
(919) 515 - 3689 Lab
(919) 515 - 7911 Field Lab
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