Absorption optics data processing with standard errors for sedimentation and diffusion coefficients from moving boundary ultracentrifugation

A data processing protocol is presented for moving boundary ultracentrifugation in which the boundary position and width are determined from absorption optics scanner traces. The best fitting Gaussian (normal probability) function is determined for each trace by weighted probit analysis. The boundary positions are used to determine the s-rate. The boundary spreading is used to determine the diffusion coefficient after correction for s-rate concentration dependence obtained elsewhere. Both linear and quadratic least-squares curve fittings are used. If the quadratic term is significant, it yields an estimate of concentration dependence from the boundary movement analysis and an estimate of the s-rate heterogeneity from the boundary spreading analysis.The carrying along of the internal standard errors at each step is emphasized. Suggestions for data processing and complete least-squares formulas are given.