Analytical ultracentrifugation (AUC)

Molecules will sediment when subjected to the gravitational forces applied by the centrifuge. The sedimentation rate depends on molecular mass, size and shape, ie. large, globular molecules will sediment faster than small, elongated ones. By analyzing sedimentation patterns, AUC can therefore determine particle molecular mass, size and shape. There are two types of AUC experiments: sedimentation velocity and sedimentation equilibrium. During sedimentation velocity (SV) experiments molecules sediment rapidly due to the high speeds employed. Before the start of the experiment molecules are distributed uniformly throughout the solution. However due to the high centrifugal forces, molecules become depleted from the meniscus and form a distinct solute/solvent boundary. Movement of this boundary is observed over time using either absorbance and/or interference optics and can be used to determine the sedimentation coefficient s which is a measure of size. SV experiments are ideal to assess sa