Pseudo synthetic boundary experiments: a new approach to the determination of diffusion coefficients from sedimentation velocity experiments

Abstract

In this paper, a method is presented which efficiently separates diffusion-boundary-broadening from polydispersity in sedimentation velocity experiments. This can be achieved by the already well-known extrapolation of the apparent sedimentation coefficient distributions acquired at different times to infinite time to remove the effect of diffusion. The so-derived diffusion-corrected sedimentation coefficient distribution (SCD) is then subtracted from each experimental scan in the sedimentation coefficient domain to yield the boundary-broadening exclusively by diffusion in the radial domain. By this means, experimental scans are transferred into a pseudo synthetic boundary experiment —the classical experiment for the determination of diffusion coefficients — and can be evaluated by the various, already well established methods for synthetic boundary experiments. In principle, even diffusion coefficient distributions are accessible. The advantages of the method presented are

• That any imperfections in the layering process of synthetic boundary experiments resulting in zero-time corrections are avoided.

• That even extremely large particles such as micelles or vesicles which would sediment in any synthetic boundary experiment can be investigated in terms of diffusion coefficient distributions.

• One single experiment yields the sedimentation coefficient distribution and the corresponding pseudo synthetic boundary experiment (diffusion coefficient distribution).

• The combination of sedimentation and diffusion coefficient distributions from one experiment can, in principle, yield the density or molar mass distribution, both of which are important quantities especially for highly complex mixtures.