[RASMB] Temperature calibration

Kirk C Aune kaune at sbcglobal.net
Wed Dec 22 12:49:00 PST 2004


David Hayes wrote:

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>
> 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:
>
>> ---------------------------------------------------------------------------------- 
>>
>> The older archived RASMB emails can be found at:
>> http://rasmb-email.bbri.org/rasmb_archives
>> and current archives at
>> http://rasmb-email.bbri.org/pipermail/rasmb/
>> Search All the Archives at:
>> http://rasmb-email.bbri.org/rasmb_search.html
>> ---------------------------------------------------------------------------------- 
>>
>>
>> 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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I have read this thread with interest and can no longer contain myself 
and am willing to show my vintage and detachment from the field.   
Surely, the precision of the measurements in the XL machines has been 
established by experimentation with the same samples.   In that case, 
are there not any Model E's available yet whereby a run can be made 
(where the temperature accuracy is known very well by precalibration) 
and compare that result to what is obtained in the XL machines to 
establish accuracy?   It sure sounds like what is otherwise being 
proposed is overkill. 

Secondly, I find the discussion interesting because in my days of work 
with the Model E, I was always more concerned with temperature gradients 
in the spinning metal whereby convection could set up not only erroneous 
temperatures, but also erroneous transport.  We messed with aluminum 
flashing liners in the rotor chambers when we tried to do higher 
temperature work simply out of concern for the range of heating and 
cooling available for temperature control.   It looks like I am going to 
have to familiarize myself more about the temperature control system of 
these Non model E systems that are yielding modern day analytical 
ultracentrifugation results so that I can better understand your current 
concerns.

I enjoy following all of the conversations coming through this list group.

Kirk





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