Centrifugation Ultracentrifugation

Standard laboratory equipment (bacterial incubator, centrifuge, ultracentrifuge, UV—Vis spectrometer, Nutator, magnetic stirrer, etc.)... 

Sedimentation coefficients are a measure of the velocity witli which a particle sediments in a centrifugal force field. Sedimentation coefficients are typically expressed in Svedbergs (.symbolized S), named to honor The Svedberg, developer of the ultracentrifuge. One S equals 10 . sec. 

Erlenmeyer flask, 500-mL Round-bottom flasks, 300-mL Rotary vacuum evaporator Stainless-steel centrifuge tube, 250-mL Ultracentrifuge pH meter... 

Ultracentrifuge the tubes at 84,000 for 17 h in a swing rotor (Hitachi, RPS27-2, Tokyo, Japan). Note that at the beginning and end of centrifugation, acceleration and deceleration rates should be low so as not to disturb the gradient of the tubes. 

Physical separation methods can be based on equilibrium considerations, but the majority are not. Ordinary filtration is an example of a non-equilibrium, physical method and so is ordinary centrifugation— e.g.—the separation of a precipitate from the suspending liquid using an artificial gravity field. There are separation methods, which are called filtration which are not such as gel filtration. Ultracentrifugation in a salt gradient is a physical equilibrium method. 

The ultracentrifuge is made up of an aluminium rotor several inches in diameter and it is rotated at high speed in an evacuated chamber. The solution to be centrifuged is kept in a small cell within the rotor near its periphery. The rotor can be driven electrically or by an oil or air turbine. 

Ultracentrifugation The centrifugation of samples at very high speeds. 

There are various methods for the determination of the size distribution of organic pigment particles, the most common are sedimentation techniques in ultracentrifuges and specialized disk centrifuges as well as electron microscopy. These methods require considerable experimental skill, since the results depend largely on sample preparation and especially on the quality of the dispersion. 

Figure 3.41 Moving-zone ultracentrifugation. Zones develop during centrifugation, the lower ones being heavier particles.

During ultracentrifugation, when the frictional force equals the centrifugal force and the particle achieves maximum velocity, the relative molecular mass... 

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