Centrifugation


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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

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References in periodicals archive ?
Following the vortexes, the samples were subjected to centrifugation at 4500 RPM for 25 min.
The objective of the current study is to assess the effect of delayed centrifugation on integrity of serum chemistry.
The overall culture positivity by the conventional blood culture method was 118 (29.3%) and 60 (15.0%) by the lysis centrifugation method.
Figure 3 revealed that centrifugation time affects the weight of residue.
* After second centrifugation upper two third of PRP is discarded and lower one third - platelet-rich plasma is shaken for 1 min and can be used as such or after activation with either calcium chloride or calcium gluconate.
There are two techniques with excellent characteristics such as centrifugation method and hydrothermal treatment.
There are variations in the separation media used but dextran-based sedimentation is typically used in conjunction with a Ficoll-Hypaque density gradient centrifugation step.
The AuNPs/dextran solution from 1mM [Au.sup.3+]/1% dextran sample was used to prepare AuNPs powder by spray drying on spray dryer model ADL311 (Yamato, Japan) and by centrifugation on ultra centrifuged machine model Ultra 5.0 (Hanil Science Industrial, Korea) at 30,000 rpm for 20 min.
Specifically, cell-dense 3D human cardiac tissues were rapidly fabricated by stacking human induced pluripotent stem (iPS) cell-derived cardiac cell sheets with centrifugation; then the structure and function of the cell-layered cardiac tissues were observed by two OCT systems.
Two further breast milk samples were separated by centrifugation at 5,000 or 10,000 rpm for three minutes, and the clear layer was tested as previously described.
centrifugation protocol of A-PRF is 1500 rpm 14 mins, Differ from Standard PRF Which is 2700 rpm 12 mins.
The separation of bovine X- or Y-chromosome bearing spermatozoa (X or Y sperm) has been successfully obtained through centrifugation of spermatozoa on two Percoll discontinuous density gradients.