[RASMB] 6-channel centerpieces

[John Philo]

Rasa,

What may still not be clear to you after Claus Urbanke's response is that
the big problem is creating a seal with the lower window so you can fill the
cell from the top with a pipettor (with the upper window removed) and not
have your sample run out. 

The inner lip on the special housings allows you to tension the lower window
without an upper window being present to form the seal. Claus is proposing
to use the filling hole screws to hold some tension on the centerpiece
against the bottom window. I've never tried such a procedure---I think the
correct housings are the right way to go. With the special housings these
centerpieces seal very reliably---I've never, ever had a leak.

The small sample size is a major advantage for reducing the time to reach
equilibrium (which varies as the square of the column height). With the
6-channel cell most samples will come to equilibrium in 16-24 hr; if you
used the full column height of a velocity cell that would become a week to
10 days!

John

-----Original Message-----
From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of Rasa, M.V
Sent: Tuesday, December 13, 2005 6:01 AM
To: rasmb at rasmb.bbri.org
Subject: [RASMB] 6-channel centerpieces



Dear colleagues,

We have the opportunuity to use 6-channel centerpieces for aqueous
solutions, but we don't have the special housings described in the manual. I
think(?) that it is O.K. to use 
the 2-channel housings by tightening the cell to 60 inch-pounds, screwing
it, removing the upper window, filling the channels, and finally tightening
it to 120-140 inch-pounds. I think(?) that the protruding side of the
centerpiece should be upwards. Have you tried that?

On the other hand, since the channels are quite small, should we expect
problems with analysis because of (maybe) too narrow equilibrium profiles?

Thanks,

Mircea.

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