Stable Isotope Geochemistry


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Arndt Schimmelmann <[log in to unmask]>
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Stable Isotope Geochemistry <[log in to unmask]>
Wed, 20 Jul 2005 09:59:30 -0500
text/plain (56 lines)
Hello Aaron,
We just went through a similar off-line routine calibrating methane from
lecture bottles for D/H and 13C/12H using a vacuum line. We employ a
toepler pump to collect and compress the methane into the quartz
combustion ampoule, and at the same time we cool the bottom of the
receiving ampoule with liquid nitrogen to lower the partial pressure of
the remaining gaseous methane to a few torr. This way you can transfer
more than 99% of the methane and avoid significant isotope
fractionation. No adsorbent is needed in the quartz ampoule. In a
separate e-mail to you I will provide a graph and explanatory text
outlining the procedure in more detail.

Aaron Laubhan wrote:

>I have been attempting to "freeze" methane into a quartz ampule without
>success. Samples are classified as dry methane, however I have been
>freezing out any remaining water with the standard dry ice/methanol mix.
>Raw sample pressures vary between 50-300psi, yet the silica gel technique
>has not been friendly. I cannot seem to find any guiding publications for
>the method; can anyone point me in the direction of such a paper?
>Here is what is in the quartz ampules.  1g CuO and 20 2mm silica beads. I
>cooked the beads for 4 hours at 400C to clense the nucleation sites, and
>the CuO is clean. Am I not using the right amount of beads? Anyone have
>similar problems? I appreciate any contributing thought that will aide
>progress.  Cheers.
>Aaron Laubhan
>University of Arkansas
>113 Ozark Hall
>Fayetteville, AR 72701
>[log in to unmask]

Arndt Schimmelmann, Ph.D.
Senior Scientist
Indiana University
Department of Geological Sciences
Biogeochemical Laboratories
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Bloomington, IN 47405-1405
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home (812) 339-3708
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