Paul,
If you put a small (~1/4") plug of quartz wool at the bottom of the insert you should be fine, along with the quartz wool at the top of the chromium oxide in the combustion reactor.  This is especially necessary if you are combusting glass fiber filters.  As long as you change the insert before too much ash builds up, the insert should come out easily.
Troy

Troy E. Gunderson
University of Southern California
Wrigley Institute for Environmental Studies
3616 Trousdale Pkwy., AHF 108
Los Angeles, CA  90089-0371

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----- Original Message -----
From: Paul Eby <[log in to unmask]>
Date: Saturday, September 25, 2004 3:22 pm
Subject: [ISOGEOCHEM] EA insert tubes

> On our Fisons 1500 EA, we generally use insert tubes to collect sample ash.
> Lately though, I've been having trouble with them breaking when I try to
> replace them.
>
> They don't slide right out - they are at first stuck at the bottom, and
> when I try to wiggle it loose, it breaks near the bottom leaving a large
> chunk inside. That means replacing the entire combustion tube. I'm not
> running anything unusual in terms of samples, N and C in tin capsules,
> sediments and freeze dried marine tissue.
>
> The inserts have the slits cut into them, so I suspect that sample residue
> is seeping through and fusing with the quartz outer tube. Has anyone else
> experienced this, and perhaps have a trick or two? Do others put a small
> plug of quartz wool on top of the chromium oxide?
>
> Paul Eby
> University of Victoria
>