Modeling of Sample Dynamics in Rectangular Asymmetrical Flow Field-Flow Fractionation Channels

We model the evolution of the concentration field of macromolecules in a rectangular asymmetrical flow field-flow fractionation channel using center manifold techniques. The deviation of the primary flow from a parabolic profile influences the concentration field and this is investigated to complement previously known results. The long-term evolution of the components of the sample is shown to be well described by a one-dimensional advection-diffusion equation. The coefficients of this equation are determined by the rigorous analysis of the complete set of equations governing the two-dimensional fluid flow. This model gives quantitative predictions of the elution time of the samples, the width of the concentration pulse, and the resolution of the apparatus. The influence of initial sample width and effects of the secondary relaxation from focusing to elution conditions are discussed. Reported theoretical predictions are in agreement with experimental results published previously.