AUC is the method of choice for determination of the molecular weight of macromolecular complexes (from small polypeptides to viruses) under native solution conditions. The radial distribution of protein in the spinning cell, that arises from the action of both the outward centrifugal force and random diffusion, is mass (in a sedimentation equilibrium experiment) or mass and shape dependent (in a sedimentation velocity experiment). Numerical analysis of data can determine even very weak association constants and reveal the size distributions of solutions containing multiple species.

Our Beckman XL-I has absorption as well as interference optics able to observe sedimenting species under a wide range of buffer conditions and concentrations.