subject: Centrifugation and applications in Biotechnology brought to you by Biosystems Scientific [print this page]
Centrifugation is a process that makes use of the centrifugal force for the separation of mixtures, used in industry and in medical laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture migrate towards the axis. Chemists and biologists may increase 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". The supernatant liquid is then either quickly decanted from the tube without disturbing the precipitate, or withdrawn with a Pasteur pipette.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.
In microcentrifugation, centrifuges are run in batch to isolate small volumes of biological molecules or cells (prokaryotic and eukaryotic). Nuclei is also often purified via microcentrifugation. Microcentrifuge tubes generally hold 1.5-2 mL of liquid, and are spun at maximum angular speeds of 12000-13000 rpm. Microcentrifuges are small and have rotors that can quickly change speeds. Superspeed centrifuges work similarly to microcentrifuges, but are conducted via larger scale processes. Superspeed centrifuges are also used for purifying cells and nuclei, but in larger quantities. These centrifuges are used to purify 25-30 mL of solution within a tube. Additionally, larger centrifuges also reach higher angular velocities (around 30000 rpm) and also use a larger rotor.
When Dr. Ivan Sorvall, Beckman and IEC (International Equipment Company) came up with their "Low Speed" and "Super Speed" class centrifuges these centrifuges have been the primary fixed (EXPENSIVE) purchase in almost every lab.
Centrifugation and applications in Biotechnology brought to you by Biosystems Scientific
