Simulation of Rate‐Zonal Centrifugation on a Digital Computer

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Abstract
A numerical method is described for digital simulation of rate‐zonal centrifugation of particles with known sedimentation and diffusion coefficients in sucrose gradients at given temperatures. A model rotor based on the geometry of a B‐XIV titanium zonal rotor is used. The rotor chamber is divided into 207 annular segments by 206 equidistant cylindrical planes. Initially 207 paired values describing the concentration radius profiles of sample and gradient material together with some physical constants are provided as input data. The net fluxes of material across each plane during a short period of time are calculated. The concentrations in each segment are adjusted accordingly, yielding new concentration radius profiles. New values of density and viscosity in each segment are calculated before the next transfer of materials is allowed to take place. The iterations are continued until a predetermined cumulative run time is reached. The advantages and the drawbacks of this approach are discussed. Comparison with an actual experiment revealed that the simulation method can be used to predict final particle distribution with rather good accuracy. Moreover, the hydrodynamic stability of sample particles can be evaluated at each time point and at each distance during a centrifugation. Hence, this numerical approach can be used to optimize experimental conditions in all types of zonal centrifugation.