Hi Howard,

I can only re-emphasize what Darrell and others have pointed out
already. Whatever you do, do NOT rely solely on the claims to
purity made by your gas supplier(s).

Speaking strictly for myself, I am a great fan of a chemical getter
supplied by SUPELCO. The system consists of a loaded cartridge
and a furnace and strips your gases of all nasties such as HCs, O2
and water; as long as the furnace is on. The moment you have a
power loss and the furnace turns cold, all the trapped c@#p comes
of the trap.

To safeguard against such an eventuality I have placed a self-
indicating chemical scrubber (OMI; Supelco) behind the furnace.
Depending on what quality you feed into this scrubber line the life
span of the traps can easily exceed one year. I tend to use He of
99.999% to achieve this. One can use 99.996% He and this
scrubber line will still yield 99.9999% He but at a reduced life span
of the scrubbers.

What I like about this system is (a) it works (some scrubbers bleed
more dirt into your gas line than was present in your cylinder in the
first place) and (b) the convenience factor. Cold traps work swell
but they have to be maintained.


All the best with your lab.


Cheers,
                Wolfram




***********************************
Dr. W. Meier-Augenstein, CChem MRSC
Senior Research Fellow

University of Dundee, School of Life Sciences,
OMS, Small's Wynd, DUNDEE  DD1 4HN, United Kingdom

Tel.: +44-(0)1382-34/5124, /4574, /4968
Fax:  +44-(0)1382-34/5514

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URL1: http://www.msiwtb.dundee.ac.uk/SLSBDIV6wma.htm
URL2: http://www.dundee.ac.uk/anatphys/wma/meieraug.htm
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