BOUNDARY ANALYSIS IN SEDIMENTATION TRANSPORT EXPERIMENTS - A PROCEDURE FOR OBTAINING SEDIMENTATION COEFFICIENT DISTRIBUTIONS USING THE TIME DERIVATIVE OF THE CONCENTRATION PROFILE

A procedure is described for computing sedimentation coefficient distributions from the time derivative of the sedimentation velocity concentration profile. Use of the time derivative, ( ∂c ∂t)r, instead of the radial derivative, ( ∂c ∂r)t, is desirable because it is independent of time-invariant contributions to the optical baseline. Slowly varying baseline changes also are significantly reduced. An apparent sedimentation coefficient distribution (i.e., uncorrected for the effects of diffusion), g*(s), can be calculated from ( ∂c ∂t)r as g*(s)t = ∂c ∂tcorr 1 co ω2t2 1n( rm r) r rm2 where s is the sedimentation coefficient, ω is the angular velocity of the rotor, c0 is the initial concentration, r is the radius, rm is the radius of the meniscus, and t is time. An iterative procedure is presented for computing g*(s)t by taking into account the contribution to ( ∂c ∂t)r from the plateau region to give ( ∂c ∂t)corr. Values of g*(s)t obtained this way are identical to those of g*(s) calculated from the radial derivative to within the roundoff error of the computations. Use of ( ∂c ∂t)r, instead of ( ∂c ∂r)t, results in a significant increase (>10-fold) in the signal-to-noise ratio of data obtained from both the uv photoelectric scanner and Rayleigh optical systems of the analytical ultracentrifuge. The use of ( ∂c ∂t)r to compute apparent sedimentation coefficient distributions for purposes of boundary analysis is exemplified with an antigen-antibody system. © 1992.