Our lab uses the inserts available from Costech Analytical ($45/5). The
insert contains slots cut at one end. I place a plug of glass wool in the
tube about 1-2cm from the end (end without slots) and insert these into the
combustion column with the slots at the top. In the past I had problems with
the glass from filters running out these slots and welding the insert to the
combustion column when inserted slots down. Additionally, the insert tended
to break when I tried to remove it. I have modified a pair of tweezers to
fit into the slots at the top and with a small twist of the tweezers the
insert slides out easily. It is important to have glass wool at the surface
of your combustion reagents so that the insert does not react with the
reagent bed.

Brian Jones

Research Assistant

Dept. of Oceanography

Texas A&M University

College Station Tx. 77843

(979) 845-8916


-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Paul Eby
Sent: Saturday, September 25, 2004 5:22 PM
To: [log in to unmask]
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