As a frequent TCEA user, I had this problem once before. What we found in the end was that the ceramic itself, which was brand new, had a leak somewhere - we suspected it had somehow become porous. Like you, I had checked all the fittings to no avail. I aimed the Ar stream up the oven itself for the bottom (be careful) so that the outside of the ceramic was enveloped in Ar while still in the furnace. This caused a massive Ar spike. Changing the ceramic fixed the problem.
Bethany's TCEA test is a good one too.
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of gerard olack
Sent: Friday, March 06, 2015 3:11 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] TCEA Background Issues
Yep, that's a leak somewhere. What's the He pressure on the Conflo?
Also, if you put the dilution on, does the level of the leak drop appropriately? IF the He pressure is fine for the conflo, and diluting the flow from the TCEA reduces the m/z 40 or 28 signal appropriately, then, then it's probably not a leak going to the mass spec.
Check the flow to the conflo. If that looks fine, then if possible, hook up another device or even a He tank (use valve to adjust flow to ca. 50 to 200 mL min) to the input port for the conflo. If you've been running phosphates, you can gum up the splitter valve inside the
Conflo. That can give high backgrounds. It's a pain, but that can be
taken out and cleaned. And while your doing that, try Bethany's TCEA pressure test.
On 3/6/2015 1:44 PM, Elliot Desilets wrote:
> Hello everyone,
> 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.
> Thank you,
> Elliot Desilets
> Richardson Centre for Functional Foods and Nutraceuticals University
> of Manitoba Winnipeg, Manitoba, Canada