CENTRIFUGES

A laboratory centrifuge is an equipment which spins liquid samples at high speed for the separation of substances. Centrifuges work by the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density. Centrifuges are found in most research and clinical laboratories and used to purify cells, subcellular organelles, viruses, proteins, and nucleic acids.

Laboratory centrifuges can be categorized as minicentrifuges, microcentrifuges, clinical centrifuges, multipurpose high-speed centrifuges (also called as general-purpose high-speed centrifuges), and ultracentrifuges. Minicentrifuges and microcentrifuges are designed for small tubes from 0.2 ml to 2.0 ml and can obtain rotational speeds of up to 15,000 rpm, and relative centrifugal force (RCF) of over 20,000 xg. Clinical centrifuges are generally moderate-speed devices used for clinical applications such as determination of volume fractions of erythrocytes in blood. General purpose high-speed centrifuges are the most common type, with volume ranges covering 0.2 to 750 ml or so. Ultracentrifuges spin samples at very high speeds, usually ranging from 60,000 rpm and 200,000 xg to 150,000 rpm and 1,000,000 xg. They are segmented into two main classes: preparative and analytical. Preparative ultracentrifuges isolate or pellet biological particles, viruses, organelles, membranes and biomolecules such as DNA, RNA and lipoproteins. Analytical ultracentrifuges use detection systems to monitor spinning samples in real time to determine sedimentation velocity and equilibrium used to determine shape and mass of macromolecules.

During centrifugation process, heat is generated due to the friction between rotating rotor and air. Heat is generated even in ultracentrifuges where the rotor operates in a good vacuum. In order to prevent sample degradation due to inconvenient temperature level inside the centrifuge chamber, many types of laboratory centrifuges are refrigerated and temperature regulated. Refrigerated centrifuges can stabilize the temperature of the chamber within the range of -10°C to +40°C (or within a wider range), making them perfect for heat-sensitive samples such as DNA, RNA or antibody.