ABSTRACT
Larger molecules or particles are usually compressed closer to the wall and thus are retained more. Hence the elution sequence proceeds from the smallest molecules or particles to the largest ones. This Field-Flow Fractionation (FFF) mode, when the intensity of driving forces induced by the applied outer field is homogenous within the entire channel, is called classical FFF. When the mean distance of Brownian motion is less than the particle radius r, steric FFF becomes operative. The mean layer thickness is thus controlled by steric exclusion of the particles from the accumulation wall, because particles cannot approach the wall closer than at the distance of their own mean radius. Separation in FFF, characterized quantitatively by retention, is accompanied, as in other separation methods, by the dynamic processes and mechanisms by which the natural tendency of the system to disperse solute zones developed on their migration down the channel is manifested.
