## Monday, October 17, 2016

### Centrifugation - Separate particles with rotational motion

Centrifugation, in simple terms, is the process of separating particles using rotational motion around an axis. At the end of centrifugation, particles are sorted out by a density gradient inside the centrifuge tube, with denser (heavier) particles at the bottom and lighter particles on top.

Centrifugation is much more efficient in creating a density gradient and separate particles by mass than just using gravity. The rotational motion of centrifugation creates strong force on the particles inside the microfuge tube. In particular, the particles will be impacted by the centripetal force, which is proportion to the centripetal components of the linear acceleration in rotational motion of the centrifuge.

For example, a minicentrifuge can reach maximum speed of 10,000 rpm (revolutions per minute). Assume sample is 0.08 m from the rotation axis of the centrifuge.

10,000 rmp = 10,000*2π/60 =1047.2 rad/s
So: αR = ω2r = 1047.22 * 0.08 = 87729.8 rad/s2 = 8952.02 g’s

Using rotational motion, the minicentrifuge is able to get the sample to move at a centripetal acceleration that is about 9000 times larger than gravitational acceleration, thus the centripetal force is 9000 times larger than gravity for the same sample.