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The ultracentrifuge is a
centrifuge A centrifuge is a device that uses centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of ref ...
optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as (approx. ). There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge. Both classes of instruments find important uses in molecular biology,
biochemistry Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
, and
polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of line ...
science.Susan R. Mikkelsen & Eduardo Cortón. Bioanalytical Chemistry, Ch. 13. Centrifugation Methods. John Wiley & Sons, Mar 4, 2004, pp. 247-267.


History

In 1924 Theodor Svedberg built a centrifuge capable of generating 7,000 g (at 12,000 rpm), and called it the ultracentrifuge, to juxtapose it with the Ultramicroscope that had been developed previously. In 1925-1926 Svedberg constructed a new ultracentrifuge that permitted fields up to 100,000 g (42,000 rpm). Modern ultracentrifuges are typically classified as allowing greater than 100,000 g. Svedberg won the
Nobel Prize in Chemistry Nobel may refer to: * Nobel Prize, awarded annually since 1901, from the bequest of Swedish inventor Alfred Nobel Companies * Akzo Nobel, the result of the merger between Akzo and Nobel Industries in 1994 * Branobel, or The Petroleum Production ...
in 1926 for his research on colloids and proteins using the ultracentrifuge.Joe Rosen; Lisa Quinn Gothard.
Encyclopedia of Physical Science
'. Infobase Publishing; 2009. . p. 77.
The vacuum ultracentrifuge was invented by Edward Greydon Pickels in the Physics Department at the
University of Virginia The University of Virginia (U.Va. or UVA) is a Public university#United States, public research university in Charlottesville, Virginia. It was founded in 1819 by Thomas Jefferson, one of the Founding Fathers of the United States. It is the f ...
. It was his contribution of the
vacuum A vacuum is space devoid of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are ...
which allowed a reduction in
friction Friction is the force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), ...
generated at high speeds. Vacuum systems also enabled the maintenance of constant
temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is ...
across the sample, eliminating
convection current Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see bu ...
s that interfered with the interpretation of sedimentation results.Elzen B. ''Vacuum ultracentrifuge.'' In: Encyclopedia of 20th-Century Technology, Colin Hempstead & William Worthington, eds. Routledge, 2005. p. 868. In 1946, Pickels cofounded Spinco (Specialized Instruments Corp.) to market analytical and preparative ultracentrifuges based on his design. Pickels considered his design to be too complicated for commercial use and developed a more easily operated, “foolproof” version. But even with the enhanced design, sales of analytical centrifuges remained low, and Spinco almost went bankrupt. The company survived by concentrating on sales of preparative ultracentrifuge models, which were becoming popular as workhorses in biomedical laboratories. In 1949, Spinco introduced the Model L, the first preparative ultracentrifuge to reach a maximum speed of 40,000 Revolutions per minute, rpm. In 1954, Beckman Instruments (later Beckman Coulter) purchased the company, forming the basis of its Spinco centrifuge division.


Instrumentation

Ultracentrifuges are available with a wide variety of rotors suitable for a great range of experiments. Most rotors are designed to hold tubes that contain the samples. ''Swinging bucket rotors'' allow the tubes to hang on hinges so the tubes reorient to the horizontal as the rotor initially accelerate. ''Fixed angle rotors'' are made of a single block of material and hold the tubes in cavities bored at a predetermined angle. ''Zonal rotors'' are designed to contain a large volume of sample in a single central cavity rather than in tubes. Some zonal rotors are capable of dynamic loading and unloading of samples while the rotor is spinning at high speed. Preparative rotors are used in biology for pelleting of fine particulate fractions, such as cellular organelles (Mitochondrion, mitochondria, microsomes, ribosomes) and viruses. They can also be used for gradient separations, in which the tubes are filled from top to bottom with an increasing concentration of a dense substance in solution. Sucrose gradients are typically used for separation of cellular organelles. Gradients of caesium salts are used for separation of nucleic acids. After the sample has spun at high speed for sufficient time to produce the separation, the rotor is allowed to come to a smooth stop and the gradient is gently pumped out of each tube to isolate the separated components.


Hazards

The tremendous rotational kinetic energy of the rotor in an operating ultracentrifuge makes the catastrophic failure of a spinning rotor a serious concern, as it can explode spectacularly. Rotors conventionally have been made from high strength-to-weight metals such as aluminum or titanium. The stresses of routine use and harsh chemical solutions eventually cause rotors to deteriorate. Proper use of the instrument and rotors within recommended limits and careful maintenance of rotors to prevent corrosion and to detect deterioration is necessary to mitigate this risk. More recently some rotors have been made of lightweight carbon fiber composite material, which are up to 60% lighter, resulting in faster acceleration/deceleration rates. Carbon fiber composite rotors also are corrosion-resistant, eliminating a major cause of rotor failure.Piramoon, Sheila. "Carbon fibers boost centrifuge flexibility: advancements in centrifuge rotors over the years have led to improved lab productivity." Laboratory Equipment Mar. 2011: 12+. General Reference Center GOLD. Web. 15 Feb. 2015.


See also

*Analytical ultracentrifugation *Gas centrifuge * Theodor Svedberg *Differential centrifugation *Buoyant density ultracentrifugation *Zippe-type centrifuge


References

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External links


07702/pdf Modern Analytical Ultracentrifugation in Protein Science: A tutorial reviewAnalytical Ultracentrifugation as a Contemporary Biomolecular Research Tool.Multi-signal analysisGilbert-Jenkins theory
Centrifuges