This might be related: once we purchased a glassy carbon tube directly
from an importer who brought them into the US from the company in
France (I think) who made them. They were cheaper than what Finnigan
was selling them for. Our results were horrible. When we examined the
tube under the microscope, we found that it was filled with little
holes! It was absolutely worthless.
So now we buy the whole reactors from Finnigan and pay the price.
Apparently these are guaranteed and we've never had a problem with
I suggest that you look at the glassy carbon tube under a binocular
microscope. The other thing we noticed in an earlier tube, was that we
had all sorts of different elements in the carbon tube after being used
for some time. They were identified by Raman spectroscopy.
On Dec 16, 2004, at 5:01 PM, Dachun Zhang wrote:
> Hi, David:
> We used to have tailing or fat peak problem of CO with our
> Isoprime-EA. It
> turned out to be the aging glassy-C tube that got more or less porous
> absorb CO. The situation is much worse for water samples then solids.
> changed a new carbon tube and the problem was gone.
> ----- Original Message -----
> From: "David Harris" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, December 16, 2004 11:36 AM
> Subject: [ISOGEOCHEM] CO peak tailing
>> 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
>> of the CO peak which I have been unable to cure. I'm out of ideas as
>> what to try next.
>> Here are some things I have already tried.
>> 1. The tailing is similar whether I try organic (eg sucrose) or
>> (eg silver nitrate) samples.
>> 2. Changing the reactor temperature between 1200 and 1400 has no
>> 3. Baking the molecular sieve GC column did not help
>> 4. Reassembing the reactor numerous times including replacing the
>> 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
>> phone 530 754 7517
>> fax 530 752 4361
Dr. Marilyn L. Fogel
Carnegie Institution of Washington
5251 Broad Branch Rd., NW
Washington, DC 20015
(Main Office: 202-478-8900)