The helium stream in commercial TC/EA systems enters from the top. For
the tube-in-tube design, it separates into two separate streams, one
passing by on the outside of the glassy carbon tube, the other going
through the core. The major flow resistance is - of course - the GC.
However, when the density inside the reactor changes due to the addition
of sample ash and silver or due to a further carbon build up, the
partitioning of the helium changes and a tail in the product gases will
emerge. We have solved the problem by feeding the He from the bottom, so
that the core flow remains constant. The corresponding paper mentioned
in an earlier communication has been accepted and will appear in RCM
soon (M. Gehre et al).
If the tail is exclusive on CO (any H2 tailing will be small in
comparison to CO) the 5A GC column might need a bakeout (over the
weekend at 250 to 300 C).
Regards   Willi

[log in to unmask] wrote:

>Hi Dachun:
>
>Are you changing the glassy carbon chips too?  I have found that upper chips, which are in contact with the samples become altered (rims form, light brown to white in color), and are perhaps becoming porous.  And, this situation can lead to the tailing you are observing.  I would ask some other groups that run jus water and see if they have to change out the liner often or not.  We run solids and our carbon liner is fine after three years.
>
>All the best,
>
>Bill Anderson
>Earth Sci. Dept./SERC
>FIU
>
>
>

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Willi A. Brand, Stable Isotope Laboratory      [log in to unmask]

Max-Planck-Institute for Biogeochemistry

Beutenberg Campus
Hans-Knoell-Str. 10, 07745 Jena, Germany      Tel: +49-3641-576400
P.O.Box 100164,      07701 Jena, Germany      Fax: +49-3641-57-70

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