With regard to the use of molecular sieve to adsorb N2 for isotope ratio
measurements, you can use 0.5nm molecular sieve (5 angstrom), as Bill
Showers notes. For the preparation line used in conjunction with our
original static vacuum mass spectrometer for measurement of nitrogen
isotope ratios, we used about 30 pellets of molecular sieve within a
100mm length of quartz tube (6mm OD, 4mm ID). This was cooled to -196C
with liquid nitrogen and gave complete trapping of nitrogen. (Note that
we were trapping nanomole quantities of nitrogen; you might need to
scale things up a little.)
We used a desorption temperature of 200C and the sieve traps were
maintained under vacuum (pumping) at 300C overnight (contrary to Bill's
recommendation). Further details are given in the publication by Boyd et
al.,  J. Phys. E: Sci. Instrum. 21 (1988) 876-885.

> ===========================================
Martin Miller
Planetary Sciences Research Institute,
The Open University,
Walton Hall,
Milton Keynes,
MK7 6AA
UK

Tel:  (direct) +44 1908 652011
Fax: (departmental) +44 1908 655910
E-mail:  [log in to unmask]