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