Free-solution electrophoresis with amplification of small mobility differences by helical flow

A description and theoretical analysis is given of a free-solution, three-dimensional electrophoretic field-flow fractionation separation in a concentric circular annulus, in which an axisymmetric swirl flow with velocity components in the axial and azimuthal directions is used to amplify a small difference between the electrophoretic mobilities of two species in a radial electric field. Separation is achieved in the azimuthal direction. The potential of this process is illustrated by calculations (neglecting diffusion) of azimuthal separations of β-lactoglobulins A and B, and racemic denopamine complexed to a stereoselective cyclodextrin. The relative mobility difference for the β-lactoglobulins is about 7%, while that the denopamine enantiomers (one of which is a potent cardiotonic agent) is about 2%. (Diffusionless) separations of 180° can be achieved with relatively modest angular rotation rates.