[RASMB] 3mm centerpieces

Kristian Schilling schilling at nanolytics.de
Sun Sep 17 23:02:45 PDT 2006


Tom and Borries,

I am wondering whether we might modify cell housings to overcome that 
problem. There is no other need for equal spacers but to align the 
centerpiece with the filling holes, so we might just drill the filling 
holes at a modified position. Of course that would mean that these housings 
can be used only with 3-mm-cps, but the first question is: can we match the 
ideal position for the centerpiece and enhance data quality?

Kristian

At 01:07 15.09.2006 -0400, you wrote:
>Hi-
>The spacers for the 3 mm centerpieces place the centerpiece at the 
>mid-point of the cell, which is out of focus for the interference system, 
>which is focused at the 2/3 plane of a 12-mm centerpiece, with sapphire 
>windows and a solvent refractive index of water. Mis-focusing will lead to 
>mis-registration of the true radial position with the apparent radial 
>position in regions of the image with steep gradients in the concentration 
>(1). For the 3 mm centerpieces, the focal plane is below the sample 2/3 
>plane, causing steeper fringes than might be expected... i.e. analysis 
>will reveal what appears to be a weak association or a heterogeneous 
>system. This problem would also affect the absorbance system, but the 
>absorbance optics cannot trace a steep enough gradient.
>So long as you keep gradients low enough (as I recall, about 50 fringes 
>displacement per mm), your data will be OK.
>Best wishes,
>Tom
>
>(1)    D. A. Yphantis. Equilibrium Ultracentrifugation of Dilute 
>Solutions. Biochemistry 3:297-317, 1964.
>
>Borries Demeler wrote:
>>Question about 3 mm centerpieces - the spacers that come with them seem
>>to take it out of the focal plane for the interference system, at least
>>we cannot get 3 mm CPs to work in interference mode. Are there spacers
>>that will correct this issue, or is there something else we should try?
>>
>>thanks, -Borries
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>>
>
>--
>Department of Biochemistry and Molecular Biology
>University of New Hampshire
>Rudman Hall 379
>46 College Road
>Durham, NH 03824-3544
>Phone: 603-862-2459
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>
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Nanolytics
Gesellschaft fuer Kolloidanalytik mbH
Dr. Kristian Schilling

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