Dave,

I had similar trouble with running cellulose samples for oxygen on our
TC/EA, and also had little luck in finding the source of the trouble. If I
looked at hydrogen, the peak shape was fine - which means that it was the
reactivity of the CO that was the problem.

The most likely source of trouble in my mind is then interaction with the
ceramic tube, but none of the fiddling I did with the reactor packing
seemed to help.

I'd be very interested if you were able to come up with a solution, so
please keep posting your findings.

Paul Eby
University of Victoria


At 11:36 AM 12/16/2004, you wrote:

>I have a TC-EA system based on the Hekatech furnace with glassy carbon tube
>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 the
>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
>http://stableisotopefacility.ucdavis.edu
>phone 530 754 7517
>fax 530 752 4361
>