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  Date: Wed, 20 Apr 94 18:31 GMT


Forwarded to:      smtp@smtp@unimelb[]
Comments by:       Geoff Howlett@BioChem@UNIMELB

A late breaking message from Walter concerning high speed centrifugation.  

   -------------------------- [Original Message] -------------------------      
Hi, Jeff - 
	I was away for a few days and just saw the exchanges
re:centerpeices. To add my 2 cents, I have used all my centerprices at full
speed (56K on the E) and 60 K on the XL-A with no obvious problems. That
includes Kel-F torqued to 140 with sapphire windows and about 110-120 with
quartz windows. The other centerpieces I use routinely now are Aluminum
filled Epon synthetc boundary cells since I use them to get matched
meniscii, and I have not had any problems with them at 60K. 

	One thing I have had problems with is leaks between the sectors on
nearly every centerpiece when I first acquired them. Beckman used to make
them slightly concave ( I think they do it differently now. ) to prevent
leaks to outside world. I had to polish every centerpiece I have ever used
to eliminate these inter-sector leaks. The intersctor leaks were subtle
sometimes but showed up often as a negative OD near the base caused by
concentrated protein at the base of the sample side leaking over to the
reference side. 

	For polishing, I use a series of ground glass plates (200, 400 and
600 surface grit). I use a standard figure eight motion under running
distilled water with some detergent as a lubricant. (This is something I
learned from Dave Yphantis in graduate school. We used it to polish the new
external loading centerpieces before we could use them - which we are still
using now for equilibrium runs.)  I have been able to recover otherwise
intractable centerpieces by re- polishing them - thus avoiding vacuum
grease and very high torques to keep them from leaking. 

Best Regards, Walter 

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