a steric field - flow fractionation system including a flow channel adapted for use with a carrier stream of fluid having particles suspended therein and a force field disposed across the flow channel to cause migration of the particles to a restraining wall , thereby forming layers of particles at the restraining wall . the strength of the force field is adjusted sufficiently high to maintain the particles of a given class at the restraining wall such that particle distance from the wall is a function of steric hindrance . particle displacement by flow along the channel is thereby determined by particle size , permitting fractionation of the particles based on differential migration of the various sizes of particle classes .