[RASMB] floatation and sedim.

[Antje Voelkel]

Dear Christine,

this looks for me, like if the sedimenting material is pelleting on the 
bottom of the cell.
In case of floatation, there would be a decreasing concentration on the 
bottom and movement in the meniscus direction, but the absorption and 
fringe shift is getting higher at the bottom.
You might observe a gray area if you watch the fringe display of the 
online camera, where the concentration is to high to resolve the 
fringes/ let the laser pass the cell. In the absorbance you will have 
the same effect like on the boundary where as Helmut said, the light is 
deviated off the slit.

It is a high concentrated sample?
3mm centerpieces could help.
But you should check, if there is an concentration effect visible in the 
sedimentation coefficent, by evaluating some of the earlier and later scans.

best regards
Antje



Ariel Lustig schrieb:
> Dear  Christine, dear Colleagues,
> it may be, that in  your  case you   have  to  work  in a D2O - 
> buffer, where the  sed.velocity me  be reduced
> due  to  higher  solvent  density but  the floataion may increase. 
> Sure one  have to try  different  densities
> where  you may  catch  both  fractions  in the  same  run or to catch 
> one out of the field.
>  Apro-pos the different densities may help you
> for the determination of the density dependent fractions (seeC *H  
> Huang and J Charlton  (JBC 1971  vol* *216  8  April* )  If you speak 
> about  purification  I understand that you intend to separate preparativly
> some  fractions. At this point  I like  to mention  that  they are  
> Vertical rotors where  the tubes have approximately the same  
> diameter  as an UC cell.so , if you  have  the run-condition , speed  
> and  time 
> of  the  analytical run,  you  can copy this  condition for  the   
> vertical rotor. When the  rotor  stands  still the   fractions (bands) 
> became  horizontal and easy to suck them out.
> I agree 100 % with Kristian Schillig about the   schlieren-peak  
> inside  the   abs.phenomena, but  this  knowledge  will not  help to 
> separate  or determe  this  two  different moving  boundariesbut to 
> recgnize them. 
> good  luck  Christine.....ariel
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===============================================================

Antje Voelkel
Max-Planck-Institute of Colloids and Interfaces
Colloid Chemistry
Am Muehlenberg 1
14476 Golm
Germany

Tel: +49 331 567 -9528/ -9531
Fax: +49 331 567-9502