Centrifugering

Centrifuging, or centrifugation, is a laboratory technique that uses centrifugal force to separate components of a mixture based on density. By spinning samples at high speed, denser components sediment and form layers or pellets while lighter materials remain in the supernatant.

The key parameter is the relative centrifugal force (RCF), expressed in multiples of gravity (g). RCF depends on rotor radius and rotation speed (rpm) and is calculated by RCF ≈ 1.118 x 10^-5 x r x (rpm)^2, with r the distance from the rotor axis to the sample. Different rotors, such as fixed-angle and swinging-bucket, and instruments ranging from benchtop microcentrifuges to large ultracentrifuges, are used. Temperature control is common to preserve sample integrity.

Common approaches include differential centrifugation, where successive spins separate components by density, and density gradient centrifugation, which uses sucrose or cesium chloride gradients to achieve separation by buoyant density or sedimentation coefficient. Ultracentrifugation reaches very high g-forces and can resolve small macromolecules and organelles.

Applications cover biology and medicine: isolation of nuclei, mitochondria, ribosomes, viruses; purification of proteins and nucleic acids; preparation of lipoproteins; plasma or serum fractionation. Safety concerns include rotor balance, correct rotor insertion, and avoiding imbalanced loads that can cause mechanical failure.

History: the method emerged in the early 20th century with work by Theodor Svedberg, who developed sedimentation techniques and the unit "Svedberg" for sedimentation coefficients; the technique has become a standard tool in research and clinical laboratories.