In addition to the good suggestions made already by others, in the absence of any leaks "running in" a new ceramic tube is best done at operational temperature (e.g. 1425 C) instead of 800 C. Whenever we need to retire an old ceramic we aim to install the new one on a Friday so the new ceramic can gas out (and anneal) over the weekend. With regards to m/z 28 and 29 levels, while low background levels are desirable it is more important for these to be stable.
With regards to GC column bake-out, remember to increase the He flow (pressure) when setting the GC temperature to 300 C (at constant pressure actual He flow decreases with increasing temperature). We set He pressure on the ConFlo to 2 - 2.5 bar during bake-out.
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Elliot Desilets
Sent: 06 March 2015 19:45
To: [log in to unmask]
Subject: [ISOGEOCHEM] TCEA Background Issues
I am having great difficulty in getting our system to spec with regards to background levels. We will be using it for D and 18O analysis in urine and saliva samples. We have a thermo TCEA coupled to a Conflo 3 and a Delta V Plus. The TCEA has not been running for roughly 9 months. We have installed a new glassy carbon reactor, ceramic tube and bottom feed adapter. Peak centre levels are as follows: 40 @ 552mV, 28 @ 27850 and 32 @ 6400.
Spraying Ar on the fittings has not helped to identify the source of a potential leak, as spikes were not observed on 40. Also, when we close the TCEA from the Conflo, the levels drop (Ar ~ 50mV), indicating that the source of the background is indeed coming from the TCEA.
He and H2 tanks were recently replaced and the background levels did not improve. The capillaries in the conflo are all at the required heights as well.
We have tried baking the GC column to 300 overnight and that improved the background somewhat, however upon cooling to operational temp, we got an error code "1999". We had to cool the reactor and re-start the system. The code went away, however, when we tried to ramp up to 300 again to bake, the code appeared again and we had to re-start again. It seems to work at operation temp (90) however I do not know the extent of the damage.
We have also baked the reactor at 800 over a weekend and that also improved the background levels, however they have seem to have stabilized.
We are running out of ideas and any help would be much appreciated.
Richardson Centre for Functional Foods and Nutraceuticals University of Manitoba Winnipeg, Manitoba, Canada
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