Jeff,

We use to use 2-3 balls of 8-12 mesh size 5A molesieve in a 6 mm
borosilicate "breakseal" to analyze N2 samples on our static RMS.  You must
degassed the molesieve on high vac (10-4 to 10-5 torr) heating it at 180
degrees C.  This can take up to 1/2 hour to completely degas the molesieve,
so we had a manifold with several breakseals degasing at once. You can
"regenerate" this molesieve at 350 degrees C in atmosphere (in a muffle
furnace), but under vacuum you can't heat it above 180 degrees or binder
will burn and it will not adsorb N2.  You can then load the N2 on the
molesieve at LN temperatures and torch off the breakseal.  We then desorb
the N2 samples off the molesieve into the inlet system of the static RMS at
a constant 40 degrees C.  We found that there can be a slight isotopic
fractionation if the room temperature changes during an analytical run.
(Actually there is up to 0.5 per mil N-15 change over a degassing
temperature range of 200 C ).

Hope this helps, we don't do this much any more since we anaylze nitrogen
dynamically in a CF-IRMS system now.  You can obtain molesieve of various
types and mesh sizes in bulk fairly inexpensively in the US from Adsorbants
and Dessicants (310) 532-6086.

Hope this helps,

Bill Showers

At 05:06 PM 11/19/98 +0800, you wrote:
>Isogeochem: I am requesting any suggestions regarding use of molecular
>sieve to absorb N2 for natural abundance measurements.
>
>Can someone share their expertise on which mole sieve to use or any advice?
>Thank you and best wishes, jeff o.
>
>===========================================
>Jeffrey S. Owen
>Academia Sinica
>Institute of Earth Sciences
>P.O. Box 1-55
>Nankang, Taipei
>Taiwan, R.O.C.  115
>
>e-mail:[log in to unmask]
>phone: +886 2 27839910 ext. 609
>fax:   +886 2 27839871
>
----------------------------------------------------------
William J. Showers
Dept. of Marine, Earth, & Atm Sciences
North Carolina State University

(919) 515-7143 - voice
(919) 515-7802 - fax
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