Effect of large refractive index gradients on the performance of absorption optics in the Beckman XL-A/I analytical ultracentrifuge: an experimental study

An analytical centrifuge cell was modified to detect refraction of light transmitted through the cell caused by refractive index gradients formed by sedimenting solute during centrifugation. Sedimentation velocity and sedimentation equilibrium experiments were carried out in this cell on solutions containing high concentrations of protein and polysaccharide in a Beckman-Coulter XLA analytical ultracentrifuge. Analysis of the results indicates that in the absence of an optical artifact easily recognized as a "black band," the dependence of apparent absorbance upon radial position reported by the instrument may be considered a reliable measure of the solute concentration gradient.