Hello Isogeochemers

Although no longer a part of the stable isotope community, I am still an
Isogeochem subscriber and would like to ask a technical question on a topic
that all mass spec users have in common. (I tried the listserver most
relevant to me but got no responses.) I am about to order replacement
molecular sieve for our foreline traps, and can't figure out what I should
get. We are using rotary pumps to back turbo pumps in pumping out a large
clean system and just want to prevent oil vapour backstreaming as well as
water contamination of roughing pump oil. There seems to be two main
choices: synthetic zeolite (generic "molecular sieve") and activated
alumina. Activated alumina is way more expensive, and I'm not sure whether
the higher cost is worth it, and if so, why. I've read suggestions that it
lasts longer between regenerations, or that it removes moisture, acids and
particulates more effectively than synthetic zeolite. If the activated
alumina really is less trouble in terms of frequency of bakeout/replacement,
then it may be worth the difference in cost. Any advice coming from
practical experience would be appreciated.

(Then of course there is the question of bead/pellet size and shape...beads
vs. pellets? 1/8" pellets vs. 1/16" pellets? Does it matter?)

Thanks in advance

Natalie


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Natalie Morisset
J.C. Roddick Ion Microprobe Laboratory/
Laboratoire de microsonde ionique J.C. Roddick
Geological Survey of Canada/
Commission géologique du Canada
601 rue Booth St., #G-20
Ottawa, ON K1A 0E8
Tel.: (613) 992 9023
Fax: (613) 995 7291
e-mail: [log in to unmask]
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