Fundamentals of Microbiology

Centrifuge

A centrifuge separates a heterogeneous mixture of solid and liquid by spinning it.  It is a device used to separate two or more substances of different density, for example: two liquids or a liquid and a solid by using centrifugal force.  After a successful centrifugation, the solid precipitate settles to the bottom of the test tube and the clear solution, called the centrifugate is obtained.

            Centrifuge consists of a fixed base or frame and a rotating part in which the mixture is placed and then spun at high speed.  Disposable plastic or glass tubes are used to place the specimen/sample.  Tubes are placed in the rotating part in holders, so arranged that when the rotary motion beings, the test tubes swing into a slanted or a horizontal position with the open ends toward the axis of rotation; the heavier, solid part of the solution settles in the bottom of the tube and the lighter liquid part forms a layer on the top.

Types of Centrifuges

a.    Low speed: go up to about 5000 rpm.

b.    High speed: go up to about 25,000 rpm.

c.    Microcentrifuge or microfuge: These are simple machines used with 0.5 or 1.5 ml disposable plastic tubes.  Most of these machines are single speed and operate between 10,000 and 13,000 rpm.

d.    Centrifuge General Purpose (Table Top): Table top centrifuge is of robust constriction and is provided with stepless speed regulator, transparent acrylic lid and is suitable for accommodating different types and capacities of rotor heads.

e.    High Speed Refrigerated Research Centrifuge: This range of centrifuges are designed for high speed centrifuging applications.  It includes a temperature control-cum-indicator with a range of -20ºC - +40ºC, digital timer with a range of 0-99 minutes and alarm at automatic switching off, dynamic brake, zero start interlock, safety cut-off in case of imbalance and lid locking switch etc.