Nonequilibrium Theory for Field-Flow Fractionation in Annular Channels

Abstract

The principles of field-flow fractionation (FFF) and reasons for extending the FFF methodology from parallel-plate channels to annular channels (ANNCs) are briefly reviewed. A theory for the nonequilibrium plate height H of FFF zones in ANNCs is developed by extending the nonequilibrium theory of FFF to polar coordinates. The principal assumption in the theory is that component zones are localized near the ANNC walls by the general force F = A/rⁿ , where A and n are constants and r is the radial coordinate. Equations for H are developed as functions of n, the inner-to-outer radius ratio of the ANNC, and the fundamental FFF parameter, γ. A closed-form analytical solution to H is obtained when n = 1; the n ≠ 1 solution must generally be expressed as a ratio of the integrals involved. These integrals can be approximated analytically, however, when γ ? 1. The functions for H are compared to their parallel-plate counterpart, and differences are rationalized.