Sedimentation Analysis in a Preparative Ultracentrifuge

Sedimentation coeflicients are usually determined in a Beckman Model E analytical ultracentrifuge. This sophisticated instrument is equipped with 

This is usually done with both species contained in one density gradient or in two identical gradients spinning in the same rotor. Since most macromolecules move at nearly constant rates, 

A useful relationship that may be derived from a linear time dependence of sedimentation relates, the speed and time of centrifugation. These two parameters may be varied as long as the product of the force and its duration are constant  

Example. 40S ribosomal subunits sediment to the center of a 10 to 20% sucrose density gradient when the gradient is centrifuged for 140 minutes at 49,000 rpm. How fast must this gradient be centrifuged if the same result is to be observed in only 100 minutes Since r must be assumed constant. 

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