Development of electrical field-flow fractionation

Electrical field-flow fractionation (ElFFF) results for a series of polystyrene latex beads are presented. To first approximation, retention behavior can be related to conventional FFF theory, modified to account for a particle-wall repulsion effect. Size selectivity and column efficiency were exceptionally high, again approaching the upper limit predicted by theory. For the channel described in the present study, application of small voltages (typically less than 2 V) across the thin (131 microm) separation space defined by a Teflon spacer generates nominal field strengths of 10(4) V m(-1). However, electrode polarization reduces the effective field across the bulk of the channel to approximately 3% of the nominal value in the system studied. The magnitude of the applied field was calibrated by using standard latex beads of known size and mobility. Perturbations to retention behavior, such as overloading, were investigated. It was found that ideal separations occur at very dilute concentrations of the sample plug and that working in systems of very low ionic strength, the double-layer thickness adds significantly to the effective size of a particle. Steric inversion was observed at a particle size of approximately 0.4 microm under the conditions employed.