Ultracentrifuge(redirected from ultracentrifugations)
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a device for separating particles less than 100 nanometers in size, such as colloids, subcellular particles, and macromolecules of proteins, nucleic acids, lipids, polysaccharides, and synthetic polymers, which are suspended or dissolved in a liquid. This is achieved by the rapid rotation of a rotor, which creates a centrifugal field with an acceleration many orders greater than the acceleration of gravity.
Ultracentrifuges are classified as preparative, analytical, or preparative-analytical according to their purpose and design.
Preparative ultracentrifuges are equipped with fixed-angle rotors, which have recesses for test tubes, beakers, or bottles, tilted at an angle of 20°-40° to the vertical axis of the rotor. Some have swinging-bucket rotors, with beakers that tilt 90° upon rotation. There are also ultracentrifuges with zonal or continuous-action rotors, with a single large vessel for the liquid being fractionated. Preparative ultracentrifuges are used to isolate individual components from complex mixtures.
Analytical ultracentrifuges have rotors with through-cylindrical recesses, in which special transparent vessels are inserted for the solutions or suspensions to be analyzed. The redistribution of particles in the solutions and suspensions may be observed directly during rotor rotation with the aid of special optical systems, such as refractometric or absorption devices. Some analytical ultracentrifuges are connected to electronic computers, which carry out the automatic processing of experimental data.
The first ultracentrifuge, designed for studying the motion of particles invisible under a microscope, was constructed by the Swedish scientist T. Svedberg in 1923 (discovery announced in 1924). This ultracentrifuge, in which a centrifugal force of up to 5,000 g was achieved, had an absorption optical system and was used to study the motion of gold particles with a diameter of approximately 5 nanometers. In 1926, Svedberg built the first highspeed ultracentrifuge (41,000 rpm, acceleration up to 105 g), which made possible the analytical study of proteins in solutions, particularly the study of hemoglobin. In 1939 he designed an analytical ultracentrifuge with a steel rotor (65,000 rpm).
The vast majority of modern laboratory ultracentrifuges are electrically driven and have aluminum or titanium rotors. In the USSR and abroad many types of ultracentrifuges are being produced in which accelerations of up to 500,000 g are created, and the separation of particles and molecules is carried out in volumes measuring tens and hundreds of milliliters.
REFERENCESLotts, Iu. A., and A. Ia. Ozherel’ev. “Analiticheskaia ul’tratsentrifuga.” Unikal’nyepribory, 1970, no. 5.
Svedberg, T, and K. O. Pedersen. The Ultracentrifuge. Oxford, 1940.
A. D. MOROZKIN