Rolf,

This is a very interesting discussion.  We have 
run a TCEA for years and have found it to be very 
important to clean up the AgPO4 or AgNO3 samples 
that we run in the prep device to get good peak 
shapes.  Organic contaminates do cause 
tailing.  We vacuum roast the AgPO4 samples and 
put the dissolved AgNO3 samples through a SPE 
C-18 filter before precipitation.  This seems to 
work wonders on peak shape and isotopic reproducibility.

Yet some days the CO  peaks are cleaner with 
smaller tails than on other days.  I wonder if it 
has something to do with lab humidity and CO2 or 
H2O getting through the TCEA pyrolysis column.

Would it not be better to clean up the He sample 
stream with the Carbosorb and magnesium 
perchlorate trap before it goes through the GC 
instead of after like the configuration that you 
have described below?  Just a thought.

Bill

At 06:36 PM 2/1/2006, you wrote:
>I can only confirm what is said below!! There is 
>always a small amount of CO2 and water leaving 
>the furnace, the latter originating form the 
>elemental H and O from cracking water at a  temp 
>of 1440°C. To capture water and CO2 is certainly 
>reasonable and necessary. We use a little glass 
>tube (10 mm ID and 12 cm in length) down stream 
>of the furnace, containing the Carbosorb and 
>subsequently the Magnesium perchlorate. From 
>there a 1/16" stainless steel line leads the gas 
>directly to the CONFLO or any other open split 
>interface. Thats all there is to it.
>
>Rolf Siegwolf      coauthor of the Saurer et al paper (1998).
>
>
>
>__________________________________
>Dr. Rolf Siegwolf
>Lab for Atmospheric Chemistry
>Stable Isotopes and Ecosystem Fluxes
>Paul Scherrer Institut
>CH-5232 Villigen PSI
>Switzerland
>
>e-mail: [log in to unmask]
>Phone: +41 56 310 2786
>Fax     : +41 56 310 4525

William J. Showers
Dept of Marine, Earth & Atm Sciences
Box 8208
North Carolina State University
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