Basic Principles of Centrifugation

A particle, whether it is a precipitate, a macromolecule, or a cell organelle, is subjected to a centrifugal force when it is rotated at a high rate of speed. The centrifugal force, F, is defined by Equation 7.1. 

F = intensity of the centrifugal force m = effective mass of the sedimenting particle w = angular velocity of rotation in rad/sec 

The force on a sedimenting particle increases with the velocity of the rotation and the distance of the particle from the axis of rotation. A more common measurement of F, in terms of the earth s gravitation force, g, is relative centrifugal force, RCF, defined by Equation 7.2. 

Although this introduction outlines the basic principles of centrifugation, it does not take into account other factors that influence the rate of particle sedimentation. Centrifuged particles migrate at a rate that depends on the mass, shape, and density of the particle and the density of the medium. The centrifugal force felt by the particle is defined by Equation 7.1. The term m is the effective mass of the particle, that is, the actual mass, 

A diagram illustrating the variation of RCF with r, the distance of the sedimenting particles from the axis of rotation. Courtesy of Beckman Instruments, Inc. 

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PRINCIPLES OF CENTRIFUGAL FILTRATION. The basic theory of constant-pressure filtration can be modified to apply to filtration in a centrifuge. The treatment applies after the cake has been deposited and during flow of clear filtrate or freshwater through the cake. Figure 30.18 shows such a cake. In this figure,... 

This section addresses two basic principles of classification—sedimentation and field-flow fractionation—and the corresponding sizing techniques. Additionally, a chromatographic technique is briefly introduced. The focus lies on sedimentation or centrifugation analysis, which corresponds to its practical relevance for the characterisation of coUoidal suspensions. 

More recently, this method has been successfully extended by us18 to form the inverse systems, i.e. water core/polymer shell particles dispersed, initially in oil, but then transferred to an aqueous continuous phase. Clearly, whether one needs an oil or a water core depends on the nature of the active material to be released. Now one starts with a water/oil emulsion, rather than an oil/water emulsion, but the basic principles are very similar. A variety of shell polymer systems were prepared, including PMMA and poly(tetrahydrofuran) [PTHF]. The high vapor pressure liquid used in this case was in general, acetone. It turned out, however, that these water core systems are intrinsically more difficult to make than the equivalent oil core systems, because large amounts of acetone were required to dissolve the polymers initially in the water-acetone mixtures. An oil was then required which did not mix too well with acetone. In general, mineral oil worked reasonably well. In order to transfer the water core capsules into an aqueous continuous phase, the particles were centrifuged in... 

Finally, Giddings et al. [174] described an S-FFF device in which the channel was coiled along the internal wall of the centrifuge basket (see Fig. 14A,B and also Fig. 15). The basic theoretical and experimental aspects of S-FFF were discussed and the fractionation of a series of monodisperse spherical polystyrene latexes was demonstrated [174]. The principle of a rotor for S-FFF capable of being applied at low centrifugal fields corresponding to speeds up to 6000 rpm is shown in Fig. 15 [175]. 

This basic illustration helps to understand the principles underlying centrifugation and centrifugal force, and this force related to gravity. The movement of any physical matter is governed by Newton s Laws of Motion, and when considering centrifugal force it is important to also consider the centripetal force. These two form the important action-reaction force pair of circular motion, where the... 

To reliably perform qualitative and quantitative analyses on body fluids and tissue, the clinical laboratorian must understand the basic principles and procedures that affect the analytical process and operation of the clinical laboratory. These include the knowledge of (1) the concept of solute and solvent, (2) units of measurement, (3) chemicals and reference materials, (4) basic techniques, such as volumetric sampling and dispensing, centrifugation, measurement of radioactivity, gravimetry, thermometry, buffer solution, and processing of solutions, and (5) safety. ... 

CENTRIFUGAL-PUMP THEORY. The basic equations interrelating the power, developed head, and capacity of a centrifugal pump are derived for the ideal pump from fundamental principles of fluid dynamics. Since the performance of an actual pump differs considerably from that of an ideal one, actual pumps are designed by applying experimentally measured corrections to the ideal situation. 

The basic principle is that the solid or semisolid sample is suspended into an aqueous solution and left under stirring to reach equilibrium of the analyte between the solid particles and water. In some methods, the solid phase is then removed by centrifugation, while in others, it is kept in the sample during the extraction. " ... 

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