Averaged molecular weight of complex mixtures as determined by rapid measurements of diffusion

The concept of a diffusion-averaged molecular weight, Md′ is presented, and Md is defined for polydisperse samples. It is shown via oligostyrene mixtures that Md can be determined in 20 minutes with common chromatographic equipment. If Md is measured and Mn or Mw is known, the polydispersity can be obtained.