Nonequilibrium Theory of Field-Flow Fractionation

Abstract

A rather general nonequilibrium theory is developed for a new separation concept, field-flow fractionation. This treatment accounts for the axial dispersion of a solute zone in a narrow tube subject to simultaneous displacement by anisotropic diffusion and by an arbitrary group of velocity vectors representing flow and applied field contributions. To good approximation, zone dispersion is found to obey Fick's law, a result characteristic of nonequilibrium theories of chromatography. An equation for the effective diffusion coefficient is deduced. Expressions are obtained for a two-dimensional case with a general power-series expansion for flow velocity; a numerical result is acquired for a special limiting case.