Sedimentation coefficient

The sedimentation coeffiecient, s, is a way of mathmatically quantfying how a molecule moves when subjected to a centrifugal force usually within a liquid medium. It is calculated by using the following equation:

s = m(1-vp)/f

Key:

m= mass of particle

v= partial specific volume

p= density of the medium

f= frictional coefficient

(1-vp) = the buoyant force of the medium

It is usually expressed in Svedberg units (S). The larger the S value, the quicker the molecule moves. However, it is not directly proportional to the molecular weight of the molecule as is apparent in the equation above.

Several other aspects affect the sedimentation velocity including mass, a heavier molecule moves more quickly. Also, if the molecule has a shape that produces less drag, its frictional coefficient will be smaller and hence, will sediment more quickly. And lastly, the density of both the molecule and the solution affects the sedimentation velocity.