Claire,
I would check the Helium flow rate on the entrance and exit sides of the
GC column to make sure it is normal before proceeding with any other
troubleshooting. If those flow rates seem normal then put an empty
ceramic column in place to check if the problem is with the current
reactor column.
Art
>
> Hello everyone,
>
> I have a persistent but random problem with my TC/EA, but the problem is
> sporadic and I haven't managed to track down the cause.
>
> When measuring CO we observe changing retention times. The variation
> occurs between two things, firstly our "normal" run time, the N2 peak
> elutes around 200 seconds and the CO peak elutes around 350 seconds,
> secondly the "delayed" run or N2 elutes around 350 seconds and CO around
> 850 seconds. Whichever retention time is observed is consistent for the
> entire sample run.
>
> We have observed this change with the same reactor tube, same gas
> pressures, temperatures etc. The difference has occurred between loading
> different samples i.e. the only thing that has been done is closing the
> isolation valve re-loading the auto-sampler, purging it and re-opening
> the isolation valve.
>
> I have baked the GC, but this has not helped.
> I have changed the reactor several times but the problem seems random
> I have varied how I purge the samples and open the isolation valve with
> purge left on and switched off, this hasn't affected it.
> I have tried resetting the TC/EA
> I have checked the ends of each line and they all seem fine. I've
> changed several ferrules which hasn't helped.
>
> The argon background is around 5-8 mV. Stability and linearity of the CO
> ref gas are good. Mass 28, 29 and 30 backgrounds are stable.
>
> The heaters seem to be working ok, so I guess there must be something
> wrong with the carrier flow, maybe a blockage which occassionally moves?
> But I have been unable to locate it.
>
> I am just about to change the reactor again and examine the one that's
> in there to see if anything has become displaced or blocked, but if
> anyone has any experience of similar problems, I'd be very grateful for
> any insights.
>
> Many thanks in advance for your help,
>
> Claire
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--
Art Kasson
Cornell Isotope Laboratory
Dept Ecology and Evolutionary Biology
E440 Corson Hall
Tower Road
Ithaca NY 14853 USA
Phone: 607.254.1382
Fax: 607.255.8088
COIL website
http://www.cobsil.com
Isogeochem website
http://www.isogeochem.com
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