Determination of the sedimentation coefficient distribution by least-squares boundary modeling

A new method is presented for the calculation of apparent sedimentation coe fficient distribution g*(s) for the size-distribution analysis of polymers is sedimentation velocity experiments. Direct linear least-squares boundary modeling by a superposition of sedimentation profiles of ideal nondiffusin g particles is employed. It can be combined with algebraic noise decomposit ion techniques for the application to interference optical ultracentrifuge data at low loading concentrations with significant systematic noise compon ents. Because of the use of direct boundary modeling, residuals are availab le for assessment of the quality of the fits and the consistency of the g*( s) distribution with the experimental data. The method can be combined with regularization techniques based on F statistics, such as used in the progr am CONTIN, or alternatively, the increment of s values can be adjusted empi rically. The method is simple, has advantageous statistical properties, and reveals precise sedimentation coefficients. The new least-squares 1s-g*(s) exhibits a very high robustness and resolution if data acquired over a lar ge time interval are analyzed. This can result in a high resolution if data acquired over a large time interval are analyzed. This can result in a hig h resolution for large particles, and for samples with a high degree of het erogeneity. Because the method does not require a high frequency of scans, it can also be easily used in experiments with the absorbance optical scann ing system. (C) 2000 John Wiley & Sons, Inc.