Stable Isotope Geochemistry


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From: [log in to unmask] (D. Cap Introne)
Date: Wed, 9 Oct 1996 14:43:53 -0400 (EDT)
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Hello isogeochemers,

This is a multifaceted question.

First, several months ago someone posted a list of different temperatures
that one could obtain by making various slushes with different solvents,
etc. Could that person (or someone else) please repost this comprehensive

Second, I assume that all posts to the listserver are archived in some way.
Could the list owner (Andrea Lini) please explain how one can search
through the archives for older posts? Is there a search engine to
facilitate this? I'm sure that others on the list would also like to know
how to do this type of thing. This of course would make my first query

Third, I have been recently contacted to analyse delta C-13 in soil CO2.
However, these samples are "dirty" with various aromatic hydrocarbons,
methane, water and other noncondensable gases (CO2 = approx .1% total).
What is the general consensus on how best to purify/condense these samples
before I admit JP-4 inadvertantly into my mass spec?!? I have enough
experience with routine CO2 analysis to know that even trace contamination
in the inlet and source can reek havoc for weeks after the "supposed
problem" occured! Horror stories of continuously stripped and cleaned
sources, messy traces, and low precision need not apply! I propose to pass
the samples over a dry ice/ethanol (immersion cooler/ethanol) slush (-90)
to remove water, while trapping the CO2 and hydrocarbons in an adjacent
trap with Liq N2 (I guess some hydrocarbons may get trapped in the water
trap as well). Maintaining these gases (CO2 and hydrocarbons) in a frozen
state I will pump away the noncondensable gases (this may have to be done
on the fly if air oxygen partial pressures are too high (liq ox!). I will
then flash the CO2 over into another trap at Liq N2 temp, while keeping the
hydrocarbons frozen in the original trap at some temperature between the
sublimated CO2 and all the frozen (hopefully!) hydrocarbons. This is the
KEY step! What type of slush and at what temperature should I use for this
last step. It is critical to ensure that nothing "bad" gets through and I
am left with clean dry CO2, while making sure that I get 100% yield of CO2
in the transfer as well? Any and all help is appreciated. Thanks in

Several of my paleoceanography associates have warned me not to get
involved in this type of "messy" measurement. I figure if the gas is pure
CO2 after these steps, no problem. However, I do not want to compromise my
instrument in any way, so experience in these types of purifications are
far more useful than theory. I'm open to all advice though. Thanks again.


Douglas "Cap" Introne
Stable Isotope Laboratory
Sawyer Environmental Research Center
University of Maine
Orono, ME 04469

Tel. (207) 581-2192
Fax (207) 581-3490
E-mail [log in to unmask]