Critical evaluation of separation mechanisms in field-flow fractionation of macromolecules and particles

Three main mechanisms of separation in Field-Flow Fractionation, the polarization, steric, and focusing, are critically analyzed. The theoretical evaluation of these mechanisms is accompanied by supporting data from several previous and recent experimental findings. The polarization mechanism can be exploited universally for the macromolecules in solution and for small particulate species. The steric mechanism is impracticable for the separations of the macromolecules in solution. The focusing mechanism was successfully applied in high-speed separations of particulate species, including the biological cells. The major factors differentiating three mechanisms and delimiting their practical use are the strength of the effective field force, the flow-rate of the carrier liquid, and the diffusion coefficients of the separated species. Whenever the highest selectivity is preferred, the polarization and focusing Field-Flow Fractionation, performed under optimal experimental conditions, are rivaling other separation methods. The accuracy, the reproducibility and the repeatability of the field-flow fractionation analyses was evaluated by simultaneous measurements carried out in two independent laboratories. [GRAPHICS] .