Dispersion due to wall interactions in microfluidic separation systems

The transport of a solute in a straight microchannel of axially variable cross-sectional shape in the presence of an inhomogeneous flow field and an adsorption-desorption process on the wall is studied, motivated by applications to capillary electrophoresis and open-channel capillary electrochromatography. An asymptotic approach based on the long time limit is adopted that reduces the problem to the solution of a one-dimensional transport equation. The reduced model is integrated numerically to study the effects of inhomogeneous electro-osmotic flow and adsorption-desorption kinetics on solute migration and dispersion in a rectangular microchannel. The accuracy of the asymptotic equations is checked by the direct numerical solution of the original three-dimensional transport problem. (C) 2008 American Institute of Physics.