Different elution modes and field programming in gravitational field-flow fractionation 2. Experimental verification of the range of conditions for flow-rate and carrier liquid density programming

Gravitational field-flow fractionation utilises the Earth's gravitational f ield as an external force that causes the settlement of particles towards t he channel accumulation wall. Hydrodynamic lift forces oppose this action b y elevating of particles from the channel accumulation wall. Therefore ther e are several possibilities to modulate the resulting force field acting on particles in gravitational field-flow fractionation, Regarding the force f ield programming in gravitational field-flow fractionation, this work focus ed on two topics: changes of the difference between particle density and ca rrier liquid density in Brownian and focusing elution modes and influencing of lift forces achieved by changing the flow-rate in focusing elution mode . We have found and described the experimental conditions applicable to for ce field programming in the case of separations of silica gel particles by gravitational field-flow fractionation. It was shown that the effect of car rier liquid viscosity in the water-methanol system is implemented as an add itional factor enhancing the desired effect of carrier liquid density. Some other forces influencing the retention behaviour of the model particles ar e discussed. (C) 2000 Elsevier Science B.V. All rights reserved.