A comparison of evaluation methods for sedimentation velocity data of polymer solutions

Abstract

In this paper, three different methods for the calculation of the sedimentation coefficients s ₂ of the polymer from sedimentation velocity runs of bovine serum albumin solutions are compared: firstly, the calculation of s ₂ by means of the time-dependent movement of the boundary solvent/solution; secondly, the calculation of s ₂ by means of the time-dependent movement of a hypothetical infinitely sharp boundary due to Goldberg; thirdly, the determination of s ₂ with respect to the time-dependent movement of the local centre of mass of the polymer component. The results indicate that the sedimentation coefficients due to Goldberg must be about twice as large as the values due to the centre-of-mass method. The calculated values, derived from the experimental a tal nd simulated data, are in very good agreement with the theoretical relations derived in this work. The results show clearly that the method of the peak maximum of the Schlieren curve and the method of Goldberg yield nearly the same values for s ₂ and the value of infinite dilution s ⁰₂ , as it is expected for native polymers having diffusion coefficients of rather low values. A comparison between s ₂ and s ⁰₂ due to the method of Goldberg and the corresponding values due to the centre-of-mass method showed clearly the important influence of the choice of the reference system. The resulting differences, attributable to a transition from the laboratory system (Goldberg and peak maximum) to the centre-of-mass system are explained in this paper.