[RASMB] sedimentation

[John Correia]

The discussion digressed into particle size without mentioning software:  either c(s) in Schuck's sedfit or DCDT WD (wide distribution) in Stafford sedanal can handle extremely broad distributions.  Try to completely clear the meniscus and pellet even the smallest particle to get good results.  I have looked at microtubules up to 10,000 S with WD.



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 Dr. John J. "Jack" Correia
 Department of Biochemistry
 University of Mississippi Medical Center
 2500 North State Street
 Jackson, MS  39216
 (601) 984-1522                                 
 fax (601) 984-1501                             
 email address: jcorreia at biochem.umsmed.edu     
 homepage location: http://biochemistry.umc.edu/correia.html
 dept homepage location:    http://biochemistry.umc.edu/
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>>> John Coropisnita <brifcor at yahoo.com> 10/23/03 05:33AM >>>
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Dear Colleagues,

I would like to ask you the following questions
(I am performing sedimentation velocity measurements
on small silica particles).

1. Since the Beckman's software does not give 
reproducible results of sedimentation coefficient
when using the second moment method, I would
appreciate
any suggestion about a good software for determining
this coefficient as well as the diffusion coefficient.

2. In some cells I noticed that the reference (pure
grade ethanol, taken from the same vial) has an
absorbance of -0.2 to -0.5 OD, while in other cells it
is zero. I noticed this when I measured very diluted
dispersions (and not when more concentrated were
measured); The meniscus of the reference
in the above case has also a strange shape. The
phenomena was reproducible after the cell was
refilled.
The window glass was carefully cleaned.

Have you seen something similar?

Thank you very much,

Jan.

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