Analytical ultracentrifugation (AUC) is a powerful biophysical technique used to study the properties of macromolecules, such as proteins, nucleic acids, and complex mixtures, in solution. It exploits the principles of sedimentation under a high centrifugal field to provide insights into various aspects of these molecules, including their size, shape, mass, and interactions.
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Analytical ultracentrifugation observes concentration profiles during rotation, rather than only recovering a separated pellet. Sector-shaped sample cells rotate past optical detectors. Absorbance scans measure attenuation at selected radii. A Rayleigh interferometer compares a sample sector with a solvent reference, converting concentration-dependent refractive-index changes into fringe shifts. Repeating scans follows a sedimentation boundary or the approach to a stationary distribution.[ref]
Optical Systems Used for AUC by Beckman Coulter Life Sciences. Radial concentration scans, synchronized absorbance detection and reference-sector interference
For a dilute solute of buoyant mass and translational friction , radial force balance gives , where is the sedimentation coefficient. Diffusion supplies . A velocity experiment resolves boundary motion and broadening; a sedimentation equilibrium experiment instead measures . This follows from the Boltzmann distribution in centrifugal potential . The two approaches separate frictional size information from buoyant mass information; shape, hydration and solvent properties must be specified to infer a unique geometric dimension.