Hi Wolfram,

Thanks for the thoughts, It is the CO peaks primarily but both do it. 
And the TCEA was in perfect working order (new packing on the ceramic 
reaction tube, baked out GC etc...).

What seems to happen is that the little graphite crucible, that catches 
silver preventing it from running into the ceramic tube, seems to 
soften and expand preventing the sample from dropping all the way into 
the hot spot. Because we've never had this problem before but it has 
now happened twice to us and both times when running continuous samples 
of benzoic acid...I've been doing some reading online and it seems that 
graphite will adsorb aromatic acids, such as benzoic acid, I'm 
wondering if that has something to do with it. We're going to be trying 
a fresh crucible but if that doesn't work, well three times conspiracy 
and we'll know the benzoic is the culprit, just not why.

Adam

On Jul 30, 2005, at 10:18 AM, Dr W Meier-Augenstein wrote:

> Hi Adam,
>
>
> Do both peaks broaden (H2 and CO) or only the H2 peak?
>
> If its only the H2 sample peak, I'd be tempted to say something's 
> messing up the He flow in the reactor (usually spilled silver starting 
> to build up at the bottom of the reactor tube); but for that to happen 
> after only ten runs is pushing it a bit.
>
> I take it all the usual suspects have been ruled out, such as air 
> breaking in due to problems with the AS isolation valve or a GC column 
> that hasn't been baked out for a while?
>
> If both sample peaks broaden and eventually vanish, my money would be 
> on the column. Perhaps the fact it happened when you run your benzoate 
> samples was merely a coincidence.
>
>
> Cheers,
>
> Wolfram
>
>
> On Jul 29 2005, Adam Zoltan Csank wrote:
>
>> Hello all,
>> I've been attempting to run some Benzoic acid on the TCEA, however, 
>> it seems that after a little over ten samples have been run my peaks 
>> begin to tail until they they disappear. The cause of this problem is 
>> that the graphite crucible seems to be softening and degrading and so 
>> is not allowing the samples to reach the hot spot. I am wondering if 
>> maybe the benzoic acid is reacting with the graphite somehow. Or if , 
>> since we have been cleaning and reusing our crucibles, the crucibles 
>> themselves weaken over time.
>> I would be curious to know if anyone else has had this problem, and 
>> if anyone has any ideas as to what could be the cause.
>> Thanks in advance,
>> Adam
>> Adam Zoltan Csank
>> Department of Geological Sciences,
>> University of Saskatchewan,
>> 114 Science Place,
>> Saskatoon, SK, Canada,
>> S7N 5E2
>> phone (o) (306) 966-5737
>>               (h) (306) 665-2797
>> email <[log in to unmask]>
>> http://homepage.usask.ca/azc461
>>
Adam Zoltan Csank
Department of Geological Sciences,
University of Saskatchewan,
114 Science Place,
Saskatoon, SK, Canada,
S7N 5E2
phone (o) (306) 966-5737
              (h) (306) 665-2797
email <[log in to unmask]>
http://homepage.usask.ca/azc461