Retention behavior of microparticles in gravitational field-flow fractionation (GrFFF): effect of ionic strength.

Retention behavior of micron-sized particles in gravitational field-flow fractionation (GrFFF) was studied in this study. Effects of ionic strength and flow rate as well as the viscosity of the GrFFF carrier liquid was investigated on the size-based selectivity (Sd), retention ratio (R), and plate height (H) of micron-sized particles using polystyrene latex beads as model particles. It was found that the retention ratio of microparticles increases with increasing flow rate or the viscosity of the carrier liquid as the particles are forced away from the accumulation wall by increased hydrodynamic lift forces (HLF). On the other hand, the retention time increases (retention ratio decreases) with increasing ionic strength of the carrier liquid at the same flow rate, due to decreased repulsive interaction between the particles and the channel accumulation wall (glass in this study) allowing the particles approach closer to the wall. Results suggest the ionic strength of the carrier liquid plays a critical role in determining retention of microparticles in GrFFF as well as the viscosity or the flow rate of the carrier liquid. It was found that the resolution and the separation time could be improved by increasing the carrier viscosity and by carefully adjusting the ionic strength of the carrier liquid.