Laser Light-Scattering Characterization of the Molecular Weight Distribution of Dextran

Laser light scattering (LLS) including the angular dependence of the absolute integrated scattered intensity (StaticLLS) and of the line-widthdistribution (dynamic LLS) has been used to characterize the molecular weight distributions of dextran samples with different branching densities. In the procees of converting a translational diffusion coefficient distribution (G(D)) obtained from the precisely measured intensity-intensity time correlation function into a molecular weight distribution (MWD), we encountered the following two problems: the change of the dextran conformation as a function of molecular weight and the lack of a set of narrowly distributed dextran standards. A procedure to solve these two problems simultaneously has been presented, wherein the weight-average molecular weight (M,) obtained from static LLS is used to constrain the conversion of G(D) to MWD. By using this procedure, we were able to obtain a calibration of D (cm*/s) = 1.98 X 10-'M-~0~Bs7-0~Mo1 lam1 with a set of broadly distributed dextrans and to accomplish the calculation of MWD of dextran from the measured spectral distribution. The calculated molecular weight distributions are fairly comparable to the ones obtained from gel filtration experiments.