Kim:

In contrast to the comments of Moritz and Laurent, I have always placed the
Carbosorb/molecular sieve CO2 trap after the magnesium perchlorate water
trap in the Carlo Erba NA 1500 NC elemental analyzers that I have used,
following exactly the filling and placement instructions in the manual for
these instruments.  I have used these traps in this arrangement for 6 years
combusting thousands of samples without any problem.  Any water formed as a
by-product in the reaction is either insignificant compared to the amount
of water initially generated by combusting large samples of plant or soil
material for N analysis and/or adsorbed on the Carbosorb or molecular
sieve.  In fact, it is my experience that when water starts showing up in
mass scans, it can usually be traced to an exhausted magnesium perchlorate
trap.  Remember that the magnesium perchlorate trap is physically a much
smaller trap than the CO2 trap, and it's my opinion that many users do not
change the perchlorate trap frequently enough.

Steve


>Dear Steve and other interested members,
>
>Pardon me for my ignorance. Is sodium hydroxide the active ingredient in
>Carbosorb? If that is so, won't water be formed as a by-product in its
>reaction with carbon dioxide? Hence shouldn't we place Carbosorb before the
>magnesium perchlorate  water trap so that the latter could get rid of the
>water by-product.
>
>Hope to get a clarification on this standard practice.
>
>Rgds,
>Kim
>
>
>Kim Gan
>Environmental Biology
>Research School of Biological Sciences
>Australian National University
>P.O.Box 475
>ACT 2601
>Canberra, Australia
>Tel: 61-2-61252406
>Fax: 61-2-61254919
>
>>>> [log in to unmask] 02/01/01 08:15am >>>
>Kendra:
>
>I prefer to use Carbosorb in my EA CO2 traps with a small amount of 3A
>molecular sieve at the entrance and exit of the trap.  Remember, when
>using
>Carbosorb, the CO2 trap should be placed after the magnesium perchlorate
>water trap, the opposite of the order when using a soda lime trap.  It's
>my
>understanding that soda lime works best when there is a slight amount of
>water present, so it should be placed before the magnesium perchlorate
>water trap.
>
>Steve
>
>
>>Hello everyone...
>>        Does anyone feel strongly about the best type of CO2 trap to
>>use in an EA - soda lime traps vs. carbosorb traps?
>>
>>Thanks,
>>Kendra
>>
>>_________________________
>>
>>   NASA/Ames Research Center
>>   Mail Stop 239-4
>>   Moffett Field, CA  94035
>>    650-604-1430 (voice mail)
>>    650-604-6110 (lab)
>>    650-604-1088 (fax)
>
>
>---------------------------------------------------------------------------
>Stephen S. Howe                         Office:  (518) 442-5053
>Dept. of Earth & Atmos. Sciences        Stable Isotope Lab:  (518)
>442-4471
>Earth Science 352B                      FAX:  (518) 442-5825
>University at Albany                    E-mail:  [log in to unmask]
>1400 Washington Avenue        http://www.albany.edu/geosciences/sshowe.html
>
>Albany, NY  12222-0001      http://www.albany.edu/geosciences/sirmslab.html
>
>---------------------------------------------------------------------------


---------------------------------------------------------------------------
Stephen S. Howe                         Office:  (518) 442-5053
Dept. of Earth & Atmos. Sciences        Stable Isotope Lab:  (518) 442-4471
Earth Science 352B                      FAX:  (518) 442-5825
University at Albany                    E-mail:  [log in to unmask]
1400 Washington Avenue        http://www.albany.edu/geosciences/sshowe.html
Albany, NY  12222-0001      http://www.albany.edu/geosciences/sirmslab.html
---------------------------------------------------------------------------