Concentration-Dependent Sedimentation in Two-Component Systems, with Reference to Differential Boundaries

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Abstract
This paper shows that if a sedimentation velocity experiment is performed on a binary system using an initial boundary formed between solutions of slightly different concentrations, the observed data can be analyzed to evaluate s and D for any type of concentration dependence of s; here s is the sedimentation coefficient of the solute and D is the diffusion coefficient of the system. The Lamm differential equation for sedimentation of a single, homogeneous solute in the ultracentrifuge cell is solved in closed form by employing approximations which are appropriate under this initial condition. Equations for the movement of the boundary gradient curve and its height‐area ratio are derived from the approximate solution obtained. From these equations, procedures are developed which permit determination of the values of s and D for the mean concentration of the two starting solutions and the first derivative of the dependence of s on concentration at this composition.