Abstract: A method of separating small diameter non-magnetic particles of different densities by using a low magnetic saturation ferrofluid and a high magnetic gradient to produce levitation by overcoming the magnetic attraction of the particles.Application of a constant gradient field of a level below the magnetic saturation level of the ferrofluid forms the ferrofluid into a density gradient column. Each non-magnetic particle levitates to the level inside the ferrofluid having the same apparent density as the particle.The ferrofluid contains magnetic particles with a mean effective core diameter less than about 50 angstroms and a stabilizing agent layer on the particle exceeding about 50 angstroms. Perfluorinated carriers and surfactants are preferred for their relatively high intrinsic density.

Abstract: A method of separating non-magnetic particles of different densities by using a ferrofluid to produce levitation wherein compensation is made for the magnetic attraction or interaction of the particles by removing particles too small for the desired sharpness of separation or by maintaining the ratio of the interaction force to the separation force outside of theoretical limits.