A couple of things...you did say "any" ideas...
1) Deposites in the tubing/Conflo. Replace stainless steel tubing from
reactor to GC or GC to Conflo and clip off ends of capillaries going to
mass spec (just a cm or so, or replace them as well). Phosphates will
leave a deposite in the lines/conflo, halides may corrode things a bit...
2) Replace carousel with syringe adapter and use gas tight syringe to
inject Ar, or H2, or CO or N2--basically remove the reaction part out of
the equation to test system. No, I've not done that on TC/EA, but it is
useful on GCC
I think most everything else has been said already, though you may want
to double check flow rates. If it looks like you might have to replace
GC column, you can try opening the old one up, scrapping out the top bit
and repacking it, then closing it up and trying it again.
David Harris wrote:
> I have a TC-EA system based on the Hekatech furnace with glassy carbon
> in ceramic tube design. It used to work fine. Now I have severe tailing
> of the CO peak which I have been unable to cure. I'm out of ideas as to
> what to try next.
> Here are some things I have already tried.
> 1. The tailing is similar whether I try organic (eg sucrose) or inorganic
> (eg silver nitrate) samples.
> 2. Changing the reactor temperature between 1200 and 1400 has no effect
> 3. Baking the molecular sieve GC column did not help
> 4. Reassembing the reactor numerous times including replacing the glassy
> carbon tube and filling (130 mm GC 'chips' sieved to 2.5-3.5 mm + 5mm
> layer nickelized carbon) had no effect.
> 5. Increasing the spring loading on the glassy carbon tube did not help -
> the theory here was that the balance of gas flow through the inner and
> outer tubes was incorrect and that more spring pressure would increase
> flow through the inner tube.
> 6. The system is leak tight and has a low background and blank.
> What really gets me is that nothing I have tried so far had any effect -
> any ideas most welcome
> David Harris
> UC Davis Stable Isotope Facility
> Department of Agronomy
> 3112 Plant & Environmental Sciences Bldg.
> Davis, CA 95616
> phone 530 754 7517
> fax 530 752 4361