[RASMB] s values as function of cell position

[John Correia]

Jack
 
S values are typically only reproducible to a +/- 0.5% average anyway. 
But it might be useful to do a global fit with say Sedanal and then an
Fstat error bar on the average value, with and without floating rm
values.    We certainly see wavelength dependent and optical system
variation in assigning rm values.  But systematic variation by cell
1,2,3, which I presume means position 1,2,3 in a 4 hole rotor, is
unusual.  I do see reproducible variation in a six hole rotor but that
is variation by radial position, low, medium, vs high radius.  Each
velocity cell should see the same light intensity.  Do you get the same
result if cell 1 is placed in hole 2 or 3?  Is it the cell meaning a
defect in a cell which may mean convection or is it cell position?
 
 
 
-------------------------------------------------------------------
 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/
-------------------------------------------------------------------
 
 


>>> "jack kornblatt" <krnbltt at vax2.concordia.ca> 08/08/06 4:07 PM >>>

I have recently come across a problem the answer to which I cannot find
in the Archives.
The problem is this: If I run the same sample in the AUC at the same
temperature and speed over the course of 5 days, I get a distribution of
s values that has a spread of plus or minus <0.4%. The sample is quite
stable and shows no suggestion of degradation between days 1 and 4 but a
small peak (< 2% of the total) shows up on day 5. The perplexing thing
is that there are systematic differences between cells 1, 2 and 3. The s
values in cell 1 are always highest, the s values in cell 2 are lowest
and the s values in cell 3 intermediate. The differences are small. Cell
1 s values are about  0.4% less than those of cell 1. 
The samples in the three cells are the same; they were taken from the
same batch. The buffer is the same. 
The problem has only become evident recently. It was not present two
years ago but I cannot state unequivocally when it first started to
occur.
Has anyone suggestions as to cause and what might be done to correct
the problem?
 
thanks for any help you can give
jack (kornblatt)

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