Centrifugation


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to Centrifugation: Differential centrifugation

Centrifugation

A mechanical method of separating immiscible liquids or solids from liquids by the application of centrifugal force. This force can be very great, and separations which proceed slowly by gravity can be speeded up enormously in centrifugal equipment.

Centrifugal force is generated inside stationary equipment by introducing a high-velocity fluid stream tangentially into a cylindrical-conical chamber, forming a vortex of considerable intensity. Cyclone separators based on this principle remove liquid drops or solid particles from gases, down to 1 or 2 μm in diameter. Smaller units, called liquid cyclones, separate solid particles from liquids. The high velocity required at the inlet of a liquid cyclone is obtained with standard pumps. Much higher centrifugal forces than in stationary equipment are generated in rotating equipment (mechanically driven bowls or baskets, usually of metal, turning inside a stationary casing). Rotating a cylinder at high speed induces a considerable tensile stress in the cylinder wall. This limits the centrifugal force which can be generated in a unit of a given size and material of construction. Very high forces, therefore, can be developed only in very small centrifuges.

There are two major types of centrifuges: sedimenters and filters. A sedimenting centrifuge contains a solid-wall cylinder or cone rotating about a horizontal or vertical axis. An annular layer of liquid, of fixed thickness, is held against the wall by centrifugal force; because this force is so large compared with that of gravity, the liquid surface is essentially parallel with the axis of rotation regardless of the orientation of the unit. Heavy phases “sink” outwardly from the center, and less dense phases “rise” inwardly. Heavy solid particles collect on the wall and must be periodically or continuously removed.

A filtering centrifuge operates on the same principle as the spinner in a household washing machine. The basket wall is perforated and lined with a filter medium such as a cloth or a fine screen; liquid passes through the wall, impelled by centrifugal force, leaving behind a cake of solids on the filter medium. The filtration rate increases with the centrifugal force and with the permeability of the solid cake. Some compressible solids do not filter well in a centrifuge because the particles deform under centrifugal force and the permeability of the cake is greatly reduced. The amount of liquid adhering to the solids after they have been spun also depends on the centrifugal force applied; in general, it is substantially less than in the cake from other types of filtration devices. See Mechanical separation techniques

Centrifugation

 

the separation of inhomogeneous systems, such as suspensions, slurries, and emulsions, by means of centrifugal force. Centrifugation may be carried out by settling or by filtration.

A machine in which centrifugation is performed is called a centrifuge. A centrifuge that operates on the basis of settling has an unperforated rotor; the process of centrifuging with such a machine is known as centrifugal clarification. A centrifuge whose operation is based on filtration has a perforated rotor with a filter medium covering the inner surface.

Centrifugal clarification is used to separate the clarified liquid phase from a dilute suspension or to precipitate the solid phase from a concentrated suspension. Centrifugal filtration is most often employed to separate the solid phase from a suspension or slurry containing a relatively small amount of liquid.

Ultracentrifugation is used to investigate highly disperse systems and high-molecular-weight compounds, such as proteins.

REFERENCES

See references under .
References in periodicals archive ?
Key words: plasma biochemical analysis, centrifugation, microhematocrit, avian, peregrine falcon, Falco peregrinus
5) In several instances, specimens exhibiting gel flotation were introduced to our automated centrifugation and specimen delivery system.
Few remaining leukocytes or platelets were observed in the supernatant of specimens A, B, and D after centrifugation (0.
3 for gravitational force and 4 for centrifugation with changes in viscosity of resin with elapsed time.
They were ground in 20% fetal bovine serum-enriched phosphate-buffered saline in a Mixer Mill MM300 (Qiagen, Courtaboeuf, France) with one 3-mm tungsten bead and clarified by low-speed centrifugation.
Scheduled to be released in August by Nitto Boseki, the product is the world's first blood drawing tube that has required no centrifugation.
Chemical safety, and centrifugation and radioisotope data is included.
5% dextran T-70 solution into the preparation, the centrifugation was repeated for 10 min.
According to company executives, Herbamilk remains stable under strenuous stability tests, including freeze/thaw cycles, high and low temperatures and centrifugation.
In general, the present method of isolating proteins and peptides of interest comprises the steps of homogenizing a plant to produce a green juice, adjusting the pH of and heating the green juice, separating the target protein/peptide from other components of the green juice by one or more cycles of centrifugation and/or resuspension, and finally purifying proteins and peptides by such procedures as chromatography and/or salt precipitation.
Early attempts at purifying nucleic acids relied on density-gradient centrifugation, an expensive process that requires multiple steps and dangerous chemicals.