Clearing factor explained

In centrifugation the clearing factor or k factor represents the relative pelleting efficiency of a given centrifuge rotor at maximum rotation speed. It can be used to estimate the time

t (in hours) required for sedimentation of a fraction with a known sedimentation coefficient s (in svedbergs):t = (k)/(s) \omega of a centrifuge (in rad/s) and the minimum and maximum radius r of the rotor:k = (ln (r _{\rm{max})/(/) r _{\rm{min} })} \times \frac

As the rotational speed of a centrifuge is usually specified in RPM, the following formula is often used for convenience:^[1]

k = (2 . 53 ⋅ 10 ^{5} x ln (r _{\rm{max})/(/) r _{\rm{min} })}

Centrifuge manufacturers usually specify the minimum, maximum and average radius of a rotor, as well as the

k factor of a centrifuge-rotor combination.

For runs with a rotational speed lower than the maximum rotor-speed, the

k factor has to be adjusted:k _{\rm{adj} } = k \left(\frac \right)²

The K-factor is related to the sedimentation coefficient

S by the formula:T = (K)/(S)

Where

T is the time to pellet a certain particle in hours. Since S is a constant for a certain particle, this relationship can be used to interconvert between different rotors.(T _{1})/(K _{1}) = (T _{2})/(K _{2})

Where

T _{1} is the time to pellet in one rotor, and K _{1} is the K-factor of that rotor. K _{2} is the K-factor of the other rotor, and T _{2} , the time to pellet in the other rotor, can be calculated. In this manner, one does not need access to the exact rotor cited in a protocol, as long as the K-factor can be calculated. Many online calculators are available to perform the calculations for common rotors.

External links

• Beckman Coulter lab resources and manuals
• Appendix F of the Cell Biology Laboratory Manual

Notes and References

1. http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=basic-centrifugation.htm&ID=30 "Basics of Centrifugation"