Hi everyone!

I have a very specific question for my first entry to the list, but first
some necessary background:

When I was at the University of Vermont, I ordered several Schlenk tubes
from Kontes (part number 218710-0050, if anyone has their catalog) to store
50-300 micromole quantities of SO2 and CO2 produced on an offline
extraction line.  These tubes are sealed by high-vacuum valves with PTFE
shafts and PTFE wipers backed up by Viton o-rings (part number
826601-0004), but with no Viton o-ring at the tip in contact with the gas
(only the tip of the PTFE shaft).  I ordered these tubes because I had had
poor luck with glass stopcocks with leaky barrels and stems and because of
the paper by Revesz and Coplen suggesting that oxygen isotopic shifts
occurred in small CO2 samples stored in vessels with exposure to valves
with Viton and Teflon, presumably due to adsorption onto these materials. 
I was never able to reproduce the shifts they observed when I stored CO2 in
these Schlenk tubes, possibly because their valves have no Viton o-rings in
contact with the gas, but more probably because my samples were much larger
than theirs.  So, I was happy with these tubes.  Now at Northwestern, I
would like to order some more of these tubes and similar, but
smaller-volume, hydrolysis tubes (Kontes part number 896860-4010).  I'm
told by Kontes that the hydrolysis tubes now have valves with shafts and
wipers made of PEEK and without Viton tip o-rings.  They claim this
material is superior to PTFE, but I can find no mention of it nor any
information on chemical incompatibilities in my files.

So, my question is:  Has anyone had any experience with PEEK?  Does it have
any incompatibilities I should be aware of?  Will it allow me to attain a
vacuum of at least 5 x 10-7 torr like the tubes with PTFE valves?  Does it
scratch or deform any more readily than PTFE?

Any help would be greatly appreciated!

Steve  
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Stephen S. Howe                  Office:  (708) 491-8180
Northwestern University          Stable Isotope Lab:  (708) 491-8182
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1847 Sheridan Road               FAX:  (708) 491-8060
Evanston, IL  60208              e-mail:  [log in to unmask]
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