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

Abstract

Abstract. 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. o 1996 John Wiley & Sons, Inc.

Effect of Carrier Fluid Viscosity on Retention Time and Resolution in Gravitational Field-Flow Fractionation

“…Figure 4 shows GrFFF calibration curves obtained with four PS beads (8,12,20, and 40 μm) at a flow rate of 2 mL/min in the different solvents with the channel placed horizontally. In the solvent system A, the slope of the calibration curve (or the sizebased selectivity, S d ) decreases as the viscosity increases.…”

“…The particles are separated based on their size with larger ones eluting earlier than the smaller ones. GrFFF has been shown to be useful for separation of various types of micrometer-sized particles including coal particles, silica particles, − clay particles, starch granules, − yeast, − and pollens . It has also been shown that GrFFF is sufficiently gentle to allow separation of samples such as lymphocytes, red blood cells, − parasites, , stem cells, , and bacteria .…”

“…At relatively low flow rates, particles stay in close proximity to the bottom wall of the channel while they are driven along the channel by the flow (steric mode). As flow rate is increased, particles are subject to hydrodynamic lift forces (HLF) which raise them some distance above the wall to form thin equilibrium layers where gravitational and lift forces are balanced (hyperlayer or focusing mode). ,,, The HLF have been studied using the technique of sedimentation FFF which uses a centrifuge to generate the transverse force across the channel thickness. In these experiments, the flow rate and the field strength may be varied independently of one another. − Later the effect of carrier fluid viscosity was also included .…”

“…As flow rate is increased, particles are subject to hydrodynamic lift forces (HLF) which raise them some distance above the wall to form thin equilibrium layers where gravitational and lift forces are balanced (hyperlayer or focusing mode). 8,12,37,38 The HLF have been studied using the technique of sedimentation FFF which uses a centrifuge to generate the transverse force across the channel thickness. In these experiments, the flow rate and the field ABSTRACT: Gravitational field-flow fractionation (GrFFF) is a useful technique for fast separation of micrometer-sized particles.…”