[RASMB] Temperature calibration

[John Correia]

rasmb
 
I seriously doubt that you will find a much better way to calibrate
temperature than the CoCl2 approach Walter published.  Trying to use
solubility introduces factors like concentration & nucleation effects
into the mix.  It also only allows a measurement at one temperature.
 
At the intro & service Beckman courses in Palo Alto at the end of one
of the days they half-fill two sectors of a prep rotor with vacuum or
drive oil, spin overnight, & put a thermometer into the solutions to
check temperature.  Its one point per day but I guess a good way to
check even for prep centrifuges.
 
I certainly think this standardization is a good idea, & I am glad to
participate, although I must stress again I calibrate temperature and we
measure density, and density*vbar is a much larger source of error.  So
get a density meter while you're at it!
 
 I would also encourage you to recognize this is not the experts coming
to the rescue.  Any physical measurement requires calibration and
careful regulation of temperature.  This is a fact of life, not a
special event that will somehow resolve the problem for everybody & all
machines.  You must wait for temperature before hitting start, & if you
want to do careful work you must calibrate.  (I asked for a poll earlier
- if you have calibrated temperature on your XLA/I send me a note!)
 
The suggestions to do replicates is not something unique to this event.
 You must always do replicates, as a function of concentration, to
understand the behavior of your system.  The sample Arthur sends to us
will presumably be nonassociating, low charge, homogeneous, & in a
buffer near the isoelectric point.  For typical samples association,
heterogeneity or nonideal behavior are the sources of deviation.  In my
lab multiple users typically achieve 0.1 - 0.3% reproducible S values on
well behaved noninteracting systems, & this applies to joint analysis
with sedfit, DCDT+ and SEDANAL.  (For monomers the analysis method
should not be that critical - but it is the holidays, so get in the
spirit & sell away.)  I also honestly think users doing their own
analysis should be part of the experiment, for no reason other than
setting a standard & expecting the field to meet that standard.  I think
I have now crossed the PC line - 
 
happy holidays
 
 
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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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