[RASMB] 6-channel centerpieces

[Virgil Schirf]

Rasa,

We have titanium 6-channel centerpieces and housings from Nanolytics. 
The housings are much the same as the typical 2-channel centerpiece 
housings and the only way to work with them is the procedure that Claus 
described. I put in the bottom window and the centerpiece (with gaskets) 
and then put in an empty window holder, screw ring gasket and screw 
ring. The housing weren't designed with grooves so using a newer torque 
wrench, I tighten to about 60 inch-pounds and secure the assembly with 
the hole screws. Then I remove the window holder, screw ring gasket and 
screw ring, pipet in the samples, place the window assembly and screw 
ring gasket and screw ring and tighten to 120 inch-pounds. Since 
discovering this method, I haven't had any leakage problems. Although 
cumbersome, it seems to be very effective.

Virgil

John Philo wrote:

>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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>  
>

-- 

Virgil Schirf, Manager CAUMA & CLS
Department of Biochemistry, Rm 4.523U
The University of Texas Health Science Center
7703 Floyd Curl Dr.
San Antonio TX 78229-3900
Voicemail: 210 567-6590
Fax: 210 567-6595
Email: schirfv at biochem.uthscsa.edu