Electroosmotic Flow Dispersion of Large Molecules in Electrokinetic Migration

It is a common knowledge that large molecules have small diffusion coefficients. Therefore, it was thought that these molecules should generate very narrow peaks in electropherograms, because longitudinal diffusion was thought to be the only factor that contributes to band broadening in electrophoretic separation systems in capillaries and microfluidics. However, it is also common to observe that large molecules such as proteins and polymers often produce wider peaks than most small molecules. It is demonstrated in this work that dispersion of analytes during electrokinetic migration is also the results of Taylor dispersion. Similar to conventional Taylor dispersion, peak broadening is more pronounced for particles with smaller diffusion coefficients. The theoretical description of band broadening caused by electroosmotic flow dispersion (EOFD) and the experimental verification of this phenomenon are presented in this paper. The dispersion of various sized molecules, from small peptides to large proteins, in capillary electrophoresis is used as examples in this study.