[RASMB] Temperature calibration

[David Hayes]

Hi Arthur,

Thanks for being a volunteer to do the coordinating.  It is interesting to 
me to see how the temperature control (and other factors) affect the 
accuracy and precision of measurements made in the Beckman centrifuges.

I am working with Walter Stafford at BBRI.  I can volunteer to load the 
cells and run some samples (Walter hasn't said if he is on the list yet or 
not, so I'll just email now anyway).  Since we have an XLA and an XLI, 
would it be better to run on both machines?

I am also willing to be a repeat data analysis person for the group of data 
sets (using Sedfit and/or Sedanal).

Another factor affecting the final data output on different centrifuges is 
radial calibration.  Following Walter (and I believe John Philo's) advice, 
I never do radial calibrations except at 3000 rpm for either interference 
or absorbance systems.  I am also rather lazy and do not perform radial 
calibrations on the interference system very often.  Recently, Rick Cole 
was in the guts of our XLI working with the vacuum system, but after that 
it really needed a radial calibration.  Yet in Connecticut this summer, 
Jeff Lary said that their protocol was to do radial calibrations with water 
blanks at speed before every run; he seemed concerned with rotor balance 
and the true center of rotation with loaded cells.  Simply because of rotor 
stretch, these two protocols for radial calibration will result in 
different radius measurements for the final data sets.

Radial calibration and stability may not be a large source of error, but I 
think that the protocol for running the cells ought to specify the radial 
calibration protocol, or at least keep track of how various labs do it.

When doing blank subtraction with some of our older window pieces, it is 
obvious that the pits in the window come out at different radial positions 
even when the blank was taken at the same speed as the data scan.  I also 
tried using the first few scans of an equilibrium run (a low molecular 
weight sample made the boundary position obvious, so I did not use that 
part of the blank subtracted data in the fit) as a blank and found again 
that bumps on the blank turned into depression-bump pairs when subtracted.

If temperature control turns out to be a large factor of error in this 
study, I wonder if there is some kind of thermometer that could be 
"stuffed" into a cell.  Is the precision of the optical system good enough 
that a cell could be thermometer?  (Measure the expansion of alcohol or 
mercury, maybe with one of Jim Coles pointy cells turned around.  Or would 
it be possible to load some liquid crystal thermometer material and get it 
to change color.  Or something else with a melting temperature in the 
centrifuge operating range.)

Anyway, it will be fun to see the data from this project.

David Hayes


At 06:11 AM 12/22/2004, Arthur Rowe wrote:
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>Hi Everyone
>
>This is just a quick mail to indicate that if it is generally acceptable, I
>am willing to co-ordinate a set of trials along the lines that have been
>talked about. We would be willing from this lab to ship out a standard
>solution for analysis, pre-diluted and with solvent sample also so that no
>further manipulation beyond loading cells and running them to a defined
>protocol would be required.
>
>I have a list of people who have kindly indicated their willingness to
>participate. Any additions, please?
>
>And finally, this will - again if the arrangement is acceptable - be an
>'early 2005' task, as I intend to take a little time off for Christmas and
>the New Year. For which festivities I wish you, one and all, the very best
>of enjoyment!
>
>Arthur
>
>--
>*************************
>Arthur Rowe
>Lab at Sutton Bonington
>tel: +44 115 951 6156
>fax: +44 115 951 6157
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