Centrifugation

Centrifugation is a process that involves the use of the centripetal force for the separation of mixtures, used in industry and in laboratory settings. In chemistry and biology, increasing the effective gravitational force on a test tube so as to more rapidly and completely cause the precipitate ("pellet") to gather on the bottom of the tube. The remaining solution is properly called the "supernate" or "supernatant liquid". Since "supernatant" is an adjective, its usage alone is technically incorrect, although many examples can be found in scientific literature. The supernatant liquid is then either quickly decanted from the tube without disturbing the precipitate, or withdrawn with a Pasteur pipette. The rate of centrifugation is specified by the acceleration applied to the sample, typically measured in revolutions per minute (RPM) or g. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity.

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In the chemical and food industries, special centrifuges and can process a continous stream of particle-laden liquid.

Types

There are various types of centrifugation:

• Differential centrifugation
• Isopycnic centrifugation
• Sucrose gradient centrifugation

Other applications

• Separating textile.
• Removing water from lettuce after washing it.
• Separating particles from an air-flow using cyclonic separation.

See also

• Centrifuge