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Centrifugation is a process that involves the use of the centrifugal force
Centrifugal force

In classical mechanics, centrifugal force is an outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces , so named because, unlike Fundamental interaction, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act....
 for the separation of mixture
Separation process

In chemistry and chemical engineering, a separation process is used to transform a mixture of substances into two or more distinct products. The separated products could differ in chemical properties or some physical property, such as size, or crystal modification or other separation into different components....
s, used in industry and in 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 gravitation
Gravitation

Gravitation is a natural phenomenon that gives weight to objects. In everyday life, attraction due to gravity is the result of the presence of relatively large bodies, such as the Earth and the Moon....
al force on a test tube so as to more rapidly and completely cause the precipitate ("pellet") to gather on the bottom of the tube.






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Centrifugation is a process that involves the use of the centrifugal force
Centrifugal force

In classical mechanics, centrifugal force is an outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces , so named because, unlike Fundamental interaction, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act....
 for the separation of mixture
Separation process

In chemistry and chemical engineering, a separation process is used to transform a mixture of substances into two or more distinct products. The separated products could differ in chemical properties or some physical property, such as size, or crystal modification or other separation into different components....
s, used in industry and in 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 gravitation
Gravitation

Gravitation is a natural phenomenon that gives weight to objects. In everyday life, attraction due to gravity is the result of the presence of relatively large bodies, such as the Earth and the Moon....
al 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
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
 is properly called the "supernate" or "supernatant liquid". The supernatant liquid is then either quickly decanted
Decantation

Decantation is a process for the separation of mixtures, carefully pouring a solution from a container in order to leave the precipitate in the bottom of the original container....
 from the tube without disturbing the precipitate, or withdrawn with a Pasteur pipette
Pasteur pipette

Pasteur pipettes, also known as droppers or eye droppers, are used to transfer small quantities of liquids. They are usually glass tubes tapered to a narrow point, and fitted with a rubber bulb at the top....
.

The rate of centrifugation is specified by the acceleration
Acceleration

File:Acceleration.JPGFile:Acceleration components.JPGIn physics, and more specifically kinematics, acceleration is the change in velocity over time....
 applied to the sample, typically measured in revolutions per minute
Revolutions per minute

Revolutions per minute is a units of measurement of frequency: the number of Turn completed in one minute around a rotation around a fixed axis....
 (RPM) or g
G-force

The g-force of an object is its acceleration relative to free-fall. The unit of measure used is informally but commonly known as the "gee" , symbolized as g . An acceleration of 1 g is generally considered as equal to standard gravity , which is defined as precisely metre per second square...
. The particles' settling velocity
Settling

Settling is the process by which particulates settle to the bottom of a liquid and form a sediment. ]Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force....
 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 the chemical and food industries, special centrifuges can process a continuous stream of particle-laden liquid.

It is worth noting that centrifugation is the most common method used for uranium enrichment, relying on the slight mass difference between atoms of U238 and U235 in uranium hexafluoride
Uranium hexafluoride

Uranium hexafluoride , referred to as "hex" in the nuclear industry, is a compound used in the uranium Isotope separation#Centrifugal Force process that produces fuel for nuclear reactors and nuclear weapons....
 gas.

Centrifugation in Biotechnology


Microcentrifuges and Superspeed Centrifuges

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 rpms. 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.

Ultracentrifugation
Ultracentrifuge

The ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 1,000,000 g ....

Ultracentrifugation makes use of high centrifugal force for studying properties of biological particles. While microcentrifugation and superspeed centrifugation are used strictly to purify cells and nuclei, ultracentrifugation can isolate much smaller particles, including ribosomes, proteins, and viruses. Ultracentrifuges can also be used in the study of membrane fractionation. This occurs because ultracentrifuges can reach maximum angular velocites in excess of 70000 rpm. Additionally, while microcentrifuges and supercentrifuges separate particles in batch, ultracentrifuges can separate molecules in batch and continuous flow systems.

In addition to purification, analytical ultracentrifugation (AUC) can be used for determination of macromolecular properties, including the amino acid composition of a protein, the protein's current conformation, or properties of that conformation. In analytical ultracentrifuges, concentration of solute is measured using optical calibrations. For low concentrations, the Beer-Lambert law
Beer-Lambert law

In optics, the Beer?Lambert law, also known as Beer's law or the Lambert?Beer law or the Beer?Lambert?Bouguer law is an empirical relationship that relates the Absorption of light to the properties of the material through which the light is travelling....
 can be used to measure the concentration. Analytical ultracentrifuges can be used to simulate physiological conditions (correct pH and temperature).

In analytical ultracentrifuges, molecular properties can be modeled through sedimentation velocity analysis or sedimentation equilibrium analysis. In sedimentation velocity analysis, concentrations and solute properties are modeled continuously over time. Sedimentation velocity analysis can be used to determine the macromolecule's shape, mass, composition, and conformational properties. During sedimentation equilibrium analysis, centrifugation has stopped and particle movement is based on diffusion. This allows for modeling of the mass of the particle as well as the chemical equilibrium properties of interacting solutes.

Centrifugation Analysis


Lamm Equation
Lamm equation

The Lamm equation describes the sedimentation and diffusion of a solute under ultracentrifuge in traditional Circular sector-shaped cells. The Lamm equation can be written:...
Particle dispersion and sedimentation can be analyzed using the Lamm equation. The calculation of the sedimentation coefficient and diffusion coefficient is useful for determining the physical properties of the molecule, including shape and conformational changes. However, the Lamm Equation is most ideal for modeling concentrations of ideal, non-interacting solutes. Chemical reactions are unaccounted for by this equation. Additionally, for large molecular weight particles, sedimentation is not always smooth. This may lead to the overestimation of the diffusion coefficient, or oscillation effects at the bottom of a solution cell.

Sigma Analysis
Sigma Analysis is a useful tool determining centrifuge properties. It is similar to the continuity equation that relates volumetric flow rate Q, fluid velocity u, and flow path cross-sectional Area A:

In the case of sigma analysis, u is replaced by vg,the settling velocity at centripetal acceleration of g (9.81 m/s2), S replaces area, and is a property of the type of centrifuge, and Q is the input fluid flow rate. S has the same units as area.

Other applications

  • Separating textile
    Textile

    A textile is a flexible material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by Spinning raw wool fibres, linen, cotton, or other material on a spinning wheel to produce long strands known as yarn....
    .
  • Removing water from lettuce after washing it in a salad spinner
  • Separating particles from an air-flow using cyclonic separation
    Cyclonic separation

    Cyclonic separation is a method of removing particulates from an air, gas or water stream, without the use of filter s, through vortex separation....
    .


Sources

Harrison, Roger G., Todd, Paul, Rudge, Scott R., Petrides D.P. Bioseparations Science and Engineering. Oxford University Press, 2003.

http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=basic-centrifugation.htm&ID=30

http://www.public.asu.edu/~laserweb/woodbury/classes/chm467/bioanalytical/centrifugation%20notes.html

http://www.analyticalultracentrifugation.com/LammEqSolutions.htm

Dishon, M., Weiss, G.H., Yphantis, D.A. Numerical Solutions of the Lamm Equation. I. Numerical Procedure. Biopolymers, Vol. 4, 1966. pp. 449-455.

Cao, W., Demeler B. Modeling Analytical Ultracentrifugation Experiments with an Adaptive Space-Time Finite Element Solution for Multicomponent Reacting Systems. Biophysical Journal, Vol. 95, 2008. pp. 54-65.

Cole, J.L., Hansen, J.C. Analytical Ultracentrifugation as a Contemporary Biomolecular Research Tool. Methods and Reviews, 1999/2000.

Howlett, G.J., Minton, A.P., Rivas, G. Analytical Ultracentrifugation for the Study of Protein Association and Assembly. Current Opinion in Chemical Biology, Vol. 10, 2006. pp. 430-436.

Dam, J., Velikovsky, C.A., Mariuzza R.A., et. al. Sedimentation Velocity Analysis of Heterogeneous Protein-Protein Interactions: Lamm Equation Modeling and Sedimentation Coefficient Distributions c(s). Biophysical Journal, Vol. 89, 2005. pp. 619-634.

Berkowitz, S.A., Philo, J.S. Monitoring the Homogeneity of Adenovirus Preparations (a Gene Therapy Delivery System) Using Analytical Ultracentrifugation. Analytical Biochemistry, Vol. 362, 2007. pp. 16-37.

http://mrw.interscience.wiley.com/emrw/9780471140863/cp/cpps/article/ps2007/current/html

http://www.ap-lab.com/sedimentation_velocity.htm

See also

Centrifuge
Centrifuge

A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis....
 Sedimentation
Sedimentation

Sedimentation describes the motion of molecules in solutions or particle s in suspension in response to an external force such as gravitation, centrifugal force or electromagnetism....
 Lamm equation
Lamm equation

The Lamm equation describes the sedimentation and diffusion of a solute under ultracentrifuge in traditional Circular sector-shaped cells. The Lamm equation can be written:...