Penny

We have had the following problems on our GasBench which are similar to 
what you are experiencing.
Apart from the sample needle which Simon Eaton has mentioned, the GC 
column has a glass push-fit union between the guard and column which can 
develop a leak. Sometimes Thermo put epoxy either side to seal them.
The Valco valve on our system has also developed a problem. We changed 
the rotor but this made no difference. On removing the fused silica from 
the ports we found small particulates from the old rotor blocking the 
orifices causing a fluctuation in flow.

Regards

John Hill
UCL Chemistry

Penny Higgins wrote:
> All,
> 
> I've been writing to this list a lot lately. The mass spectrometer is 
> finally behaving properly and I am finally trying to fix a problem that 
> appeared just as everything else went crazy.
> 
> When I run carbonate samples using our Gas Bench, typically it takes 
> about 300 seconds for the carbon dioxide sample peak to come out. This 
> has been the case for more than a year. Then, literally overnight, this 
> changed to about 400 seconds. Nothing on the Gasbench was changed during 
> the intervening night.
> 
> Since then, I've adjusted the GC temperature, which only changes the 
> elution times by a few 10's of seconds at most. I've also adjusted the 
> Helium carrier pressure, which makes the peaks come out at the right 
> time, but the flow is so rapid that my sample peaks diminish far too 
> quickly for an adequate analysis.
> 
> What am I missing?
> 
> Thanks,
> 
> ~Penny
> 
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>                       Dr. Pennilyn Higgins
>                        Research Associate
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>                             "SIREAL"
>   Stable Isotope Ratios in the Environment Analytical Laboratory
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