where c is the solute concentration, t and r are the time and radius, and the parameters D, s, and ω represent the solute diffusion constant, sedimentation coefficient and the rotor angular velocity, respectively. The first and second terms on the right-hand side of the Lamm equation are proportional to D and sω2, respectively, and describe the competing processes of diffusion and sedimentation. Whereas sedimentation seeks to concentrate the solute near the outer radius of the cell, diffusion seeks to equalize the solute concentration throughout the cell. The diffusion constant D can be estimated from the hydrodynamic radius and shape of the solute, whereas the buoyant mass mb can be determined from the ratio of s and D
at the inner and outer radii, ra and rb, respectively. By spinning samples at constant angular velocityω and observing the variation in the concentration c(r,t), one may estimate the parameters s and D and, thence, the (effective or equivalent) buoyant mass of the solute.
References and notes
↑ O Lamm: (1929) "Die Differentialgleichung der Ultrazentrifugierung" Arkiv för matematik, astronomi och fysik21B No. 2, 1–4
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