Effect of flowrate and ionic strength on retention of nonporous micron-sized silica gel particles in gravitational field-flow fractionation

Retention of nonporous micron-sized silica gel particles in gravitational field-flow fractionation (GFFF) was investigated with respect to the activity of the hydrodynamic lift-forces and surface forces. The hydrodynamic lift-forces act near the channel wall in the same direction as repulsive electrostatic forces against the gravity so that the particles are focused. Although a complete quantitative description of the hydrodynamic lift-forces, which would enable prediction of the retention time, is not yet available, the experiments show that the magnitude of both forces is comparable with the particle effective weight and that the forces can be used for efficient separation of micron-sized particles. Higher ionic strengths of the carrier liquid attained by addition of NaCl decrease the repulsive electrostatic force and dramatically influence retention of the particles, yet to be reported in GFFF. (C) 1996 John Wiley & Sons, Inc.