Clearing factor

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 formula_1 (in hours) required for sedimentation of a fraction with a known sedimentation coefficient formula_2 (in svedbergs):
The value of the clearing factor depends on the maximum angular velocity formula_4 of a centrifuge (in rad/s) and the minimum and maximum radius formula_5 of the rotor:
As the rotational speed of a centrifuge is usually specified in RPM, the following formula is often used for convenience:
Centrifuge manufacturers usually specify the minimum, maximum and average radius of a rotor, as well as the formula_8 factor of a centrifuge-rotor combination.
For runs with a rotational speed lower than the maximum rotor-speed, the formula_8 factor has to be adjusted:
The K-factor is related to the sedimentation coefficient formula_11 by the formula:
formula_12
Where formula_13 is the time to pellet a certain particle in hours. Since formula_11 is a constant for a certain particle, this relationship can be used to interconvert between different rotors.
formula_15
Where formula_16 is the time to pellet in one rotor, and formula_17 is the K-factor of that rotor. formula_18 is the K-factor of the other rotor, and formula_19, 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.