How To Determine Molecular Weight
While there are many ways to determine the molar masses, or molecular weights, of macromolecules such as proteins, biopolymers and synthetic polymers, only one determines absolute molecular weights in solution, rapidly and effectively: Multi-Angle static Light Scattering (MALS). MALS combines the precise measurements of light scattering intensity and concentrations for a rigorous, first-principles calculation of solution-property molecular weights—making no assumptions of conformation or shape, and no perturbations to the sample. The theory of multi-angle light scattering for the determination of molecular masses is described in detail in Classical Light Scattering Theory.
While column calibration would suggest that hemoglobin is much smaller than BSA, MALS shows that they do in fact have similar molar masses. The polydispersity of hemoglobin, seen here as a trailing shoulder on the peak with decreasing molecular weight, is due to dynamic equilibrium between monomers, dimers and tetramers.