[RASMB] temperature control

[judithk at vax2.concordia.ca]

This comes from a novice
We have been doing some preliminary temperature studies using the AUC. The
assembled rotor was put into a thermostated cabinet for about two hours at
4 C. It was then transferred to the 4 C chamber of the AUC and the run was
started. At the end of the run it was clear that the rotor was not
initially at thermal equilibrium. It took about 60 minutes at speed to get
there. 
The problem was much less pronounced with runs at 25 C. At 40 C it took
about 15 minutes at speed to achieve thermal equilibrium.
My questions pertain to velocity runs:
1. Does anyone have suggestions as to how one can avoid starting runs at
one temperature and finishing at another short of letting the rotor
equilibrate o/n in the AUC? Could we, for instance, immerse the assembled
rotor in a thermostated water bath, dry it and then put it into the AUC?
It is clear that heat transfer in a vacuum or in a refrigerator is very
slow.
2. This is a character defect: I would like to use the instrument without
becoming
an expert. I have tried to figure out whether velocity runs started at one
temperature and finished at a second can yield any useful data once the
desired temperature is reached. My intuitive feeling is that the shape of
the boundary is dictated by the temperature. This does not correct itself
as the run conditions change and become stable. If this reasoning is
correct, it means that useful velocity sedimentation data cannot be taken
unless one starts, runs and finishes at the same temperature. Is there a
rule of thumb as to how much leeway is acceptable? If I would like to run
at 40 C but start at 38 C how much error is likely introduced?

Thanks for any help you can give
jack kornblatt via m. judith kornblatt

Judith Kornblatt
Dept of Chemistry and Biochemistry
Concordia University
1455 de Maisonneuve Ouest
Montreal, Qc H3G 1M8
Tel: 1 514 848 3384   FAX: 1 514 848 2868