Reference Library-
Centrifugation Calculations
Rotor Run Time
A simple equation is used to determine run time. This estimation is theoretical, as it does not calculate for viscosity, sample load, or any other issues, which may slow or speed up the separation.
T = K / S20,ω
Where:
T = Time (hr)
K = Rotor efficiency factor
S20,ω= Sedimentation coefficient
The solution to this equation will indicate the minimum run time for a rotor at a specific K factor (speed dependent) required to enable theoretical completion of product banding. K is listed by manufacturers or can be calculated as seen below.
Rotor Transfer
To determine the time to separate on a different scale rotor, for example when scaling up the time of separation, the K factors of both rotors must be known. The following equation can be used to determine the new run time.
t1 = (k1 x t2) / k2
Where:
k2 = Efficiency of Rotor 2
t2 = Run time of Rotor 2 (hr)
k1 = Efficiency of Rotor 1
t1 = Run time of Rotor 1 (hr)
Rotor Efficiency
The efficiency of rotor performance, K, factor gives an estimate of the time required to band a product of known sedimentation coefficient is a known rotor dimension at a set rotor speed. The efficiency information can also be calculated determined using the following equation.
k = |
ln (rmax/ rmin)
|
x |
1013 |
|
|
ω2 |
3600 |
Where:
ω = 0.10472 x Revolutions per minute (RPM)
rmax = Max. radial distance from the center of rotation (cm)
rmin = Min. radial distance from the center of rotation (cm)
Sedimentation
The sedimentation coefficient (S20,ω) of a particulate protein or macromolecule can be easily estimated or referenced from scientific literature. Particulate proteins will tend to fall in the range of small viruses 40S to 1500S. Using S20,ω enables run conditions to be quickly calculated. However, it is not essential to have the value for S20,ω and conditions can be determined empirically.
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