Dear Paul,

This might be a long shot but let me give it a try anyway.

> I'm hoping someone can shed some light on a problem I am having (GC-IRMS,
> MAT252). My background levels for CO2 are elevated, but on masses 45 and 46
> only. The source seems to be my Nafion trap, as the 45 (and 46) signal
> increases drastically (perhaps 200mV) when I heat the trap, and falls to
> normal when the trap is removed. Mass 44 is unaffected throughout all of
> this (~9mV).

Have you (or somebody in your lab) recently cleaned parts of your
machine with ethanol or are there any other sources of ethanol you
can identify? Ethanol gives rise both to 46 (M+) and 45 (M-H+),
which makes for interesting 2/1 and 3/1 ratios.

Of course, I'm assuming here you are running permanent gas
samples or similar, i.e. no on-line combustion. Having said that,
contaminants could still get in post combustion.

> I replaced the Nafion tubing, but am still getting the same problem.
> Another trap in the lab made from the same batch is working fine. Does
> anyone have any suggestions? What compound can give masses 45 and 46 but
> not 44? Nafion is a fluorinated polymer, but the only fluorine compound I
> can dream up that has a mass of 45 is NCF. Doesn't seem very likely....

Mind you, I still wouldn't rule our the Nafion completely and make
up a new trap with spanking new material, fresh from the
manufacturer. Just in case, belt and braces, don't you know.


Best wishes,

                             Wolfram



Dr. W. Meier-Augenstein, CChem MRSC
Senior Research Fellow

University of Dundee, Dept. of Anatomy & Physiology,
OMS, Small's Wynd, DUNDEE  DD1 4HN, United Kingdom

Tel.: +44-(0)1382-34/5124, /4574, /4968
Fax:  +44-(0)1382-34/5514

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URL: http://www.dundee.ac.uk/anatphys/wma/meieraug.htm


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