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INPUT   DATA

♥ EXAMPLE Of Input/Output

Title

Minimum radius about rotor axis, rmin		cm
Maximum radius about rotor axis, rmax		cm
Rotary speed, N		rpm
Sedimentation coefficient of particle, s		Svedberg unit

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OUTPUT   VARIABLES   &   GRAPHS

Variables	Values	Units
♦  Clearing factor, k
♦  Sedimentation time, t		hours

Pelleting During Centrifugation

A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centrifugal force is used to separate lighter and heavier molecules, i.e. cause the precipitate ("pellet") to gather on the bottom of the tube.

The time to pellet a particle in water at 20 °C through the maximum rotor path length is given by:

     t = k/s

     k = 253x10⁹log_e[r_max - r_min]/N²

where
     t = sedimentation time
     r_min = distance from centerline of rotor to top liquid in centrifuge, cm
     r_max = distance from centerline of rotor to farthest point in the centrifuge, cm
     N = speed of rotation, revolutions per minute
     s = sedimentation coefficient of particle, Svedberg unit
     k = clearing factor, a measure of the pelleting efficiency of the rotor.

Tips

    ◊ Use link EXAMPLE Of Input/Output  to demo data entry expectations and results; you may edit & use it as starting point

BIBLIOGRAPHY

• Stephenson FH; Calculations For Molecular Biology And Biotechnology: A guide to mathematics in the laboratory; Academic Press, An Imprint of Elsevier, Amsterdam, 2003
• Ratnam S & March SB; Effect of relative centrifugal force and centrifugation time on sedimentation of mycobacteria in clinical specimens; J. Clinical Microbiology, Mar 1986, 23(3): 582–585