urgent help please

Dr Engelbert Buxbaum engelbert_buxbaum at hotmail.com
Thu Jun 8 07:13:49 EST 2006


chiranjit chowdhury wrote:

> Hi!!
> You have sent a protocol in which you suggested to do centrifugation at
> 45000rpm using 45Ti rotor (Beckman).But I don't have access to this
> ultracentrifuge.We are having Sorvall ultracentrifuge.Please tell me in
> which rcf(xg)I should I have to centrifuge and which rotor (vertical,fixed
> angle or swing rotor )should I have to use.

The 45Ti is a fixed angle rotor for moderately large sample sizes. You
can transfer your method to any similar rotor using the pelleting
efficiency (k-factor):

k = \frac{t}{S} =
\frac{\ln(\frac{r_{max}}{r_{min}})*253303}{(\frac{rpm_{max}}{1000})^2}

If the rotor is not run at full speed (45000 rpm for the 45Ti) the
k-factor is corrected by

k' = k * (\frac{rpm_{max}}{rpm})^2

You can then directly transfer procedures from one rotor to another
since

\frac{k_1}{t_1} = \frac{k_2}{t_2}

with t = time, r_{max} and r_{min} the maximal and minimal radius, S =
sedimentation constant, rpm and rpm_{max} the actual and maximal rotor
speeds. k and k' are the nominal and corrected pelleting efficiencies of
the rotor in question. You may not have to calculate k, because it is
usually given in the rotor documentation, in case of the 45Ti on
Beckmans web site. 

(I used TeX-syntax to transfere these equation in an ASCII only
environment, if you can not read them, go to your computer department
and ask for a TeXnician)




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