Sedimentation Velocity Experiments

Sedimentation velocity experiments are performed at high speed to overcome the effect of diffusion. Sedimentation will separate the components in the sample providing a very sensitive assay for composition. In a velocity experiment the speed is generally so great that back diffusion from the bottom of the cell is minimal compared to the rate of sedimentation such that a moving boundary will form, behind which will be little to no material left. The evolution of the shape of the boundary over time is representative of the composition, sedimentation and diffusion properties of the sample and in ideal cases can be analyzed for molecular weight.

A diagram of sedimentation experiment

Velocity experiment: a moving boundary is generated because the rotor speed is large enough to prevent back diffusion from the cell bottom to influence the absorbance near the meniscus, which will deplete over time.

Velocity experiments are best for determining composition, assaying for contaminants, aggregates, and to distinguish reversible from noninteracting systems by comparing concentration series. Velocity experiments can provide information about relative shape (anisotropy), size and molar mass. Velocity experiments have a much higher resolution than equilibrium experiments and are recommended for most applications.