HI Effie--

When you said you lost CO2 signal, does that mean there are no peaks 
coming through or just no CO2? You can have a clog in the nafion 
tubing--the one post GC column. You can also have a clog or break in the 
sampling line--which you probably already looked at. As far as the 
column is concerned, we ended up abusing ours a bit and it partially 
clogged--you needed a lot of pressure to maintain flow rates, which can 
through off your loop file times a bit. It had to be replaced with a 
porabond one, which is more rugged.

take care

gerry

Willi A. Brand wrote:
> Dear Effie,
> If you have clean CO2 in He (and are 100 % sure of it) the GC column 
> should not be necessary. However, in the Gas Bench a typical 
> contaminant is air which you often do not recognize when only looking 
> at the CO2 masses. If O2 enters the ion source at the same time when 
> CO2 is being measured, you can and often will produce extra CO2 from a 
> reaction of the O2 with carbon in the filament. Typically, this CO2 is 
> isotopically rather heavy and gives you wrong results for your 
> samples. Another source of contamination with air concurrently present 
> in the ion source is production of NO2 (m/z 46 !). In any case, using 
> the column is a necessary precaution in routine analyses. And the 
> Poraplot Q is not very demanding in terms of maintenance, a 5A column 
> for instance needs more attention.
> Regards Willi
>
> effie wrote:
>>
>> Dear all,
>>
>> Recently I'm encountering some GC column problems on the Gas bench II 
>> we have here (it's coupled with DeltaplusXP). Basically, I lost CO2 
>> signal, and the reason for it seems to be the GC column. I might add 
>> at this point that although the signal was lost, I still have some 
>> flow through it (and for that reason it took me a while to realize 
>> the column was failing). And so, a lot of time was (is) consumed 
>> trying to get to the bottom of it.
>>
>> That brings me to wander about the purpose of the GC column here. I 
>> measure CO2 out of the headspace vials (for DIC, CO2 in carbonates 
>> d18O in water, and N2O from nitrates – on not as common occasions).
>>
>> The Poraplot column here to my (not so great) knowledge, is used for 
>> separation of gases. Other advantages that are known to me are of 
>> water absorbance, better shaped peak shapes and better peak 
>> separation. The question being asked, measuring CO2 only, do I need 
>> separation at all? Can I actually bypass the GC column and run CO2 
>> samples without having severe consequences?
>>
>> G'day,
>>
>> Effie Eliani
>>
>> (B.Sc. Geology & environmental studies)
>>
>> At the stable isotope lab
>>
>> Geological survey of Israel
>>
>> This mail was sent from mail.pineapp.net
>>
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>
> -- 
> .....................................................................
> Willi A. Brand, Stable Isotope Laboratory      [log in to unmask]
> Max-Planck-Institute for Biogeochemistry (Beutenberg Campus)
> Hans-Knoell-Str. 10, 07745 Jena, Germany      Tel: +49-3641-576400
> P.O.Box 100164,      07701 Jena, Germany      Fax: +49-3641-577400
> http://www.bgc-jena.mpg.de/
> http://www.bgc-jena.mpg.de/service/iso_gas_lab/
> .....................................................................
>