Centrifugation and its principle

Centrifugation is a process that uses centrifugal force to separate the mixture of biological particle in a liquid medium. A centrifuge is a device for separation of microorganisms from the suspended fluid using centrifugal force (g-force).The centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed.The denser components of the mixture migrate away from the axis of the centrifuge, while the less dense components of the mixture migrate towards the axis. The particles precipitate at the base of test tube after centrifuge is called as Pellet. The remaining liquid that lies above the precipitate is called a supernatent or supernate.

Principle of centrifugation

1) The centrifuge involve the s principle of sedimentation.

2) The principle of the centrifugation technique is to separate the particles suspended in liquid media under the influence of a centrifugal field. These are placed either in tubes or bottles in a rotor in the centrifuge.

3) Sedimentation is a phenomenon where suspended material settles out of the fluids by gravity. The suspended material can be particles such as clay or powder. Example, tea leaves falling to the bottom in a teacup.

4) The particles having size more than 5 micrometres are separated by simple filtration process while the particles having size 5 micrometre or less do not sediment under gravity. The central force is useful to separate those particles.The rate of sedimentation depend upon applied centrifugal force (G) being directed radially outward .

The applied centrifugal field (G ) depend upon Angular Velocity (ψ in radians/sec) Radial Distance (r in cm)  of particle from axis of rotation.

G=ψ2r