Different elution modes and field programming in gravitational field-flow fractionation - III. Field programming by flow-rate gradient generated by aprogrammable pump

Gravitational field-flow fractionation (GFFF) utilizes the Earth's gravitat ional field as an external force that causes the settlement of particles to wards the channel accumulation wall. Hydrodynamic lift forces oppose this a ction by elevating particles away from the channel accumulation wall. These two counteracting forces enable modulation of the resulting force field ac ting on particles in GFFF. In this work, force-field programming based on m odulating the magnitude of hydrodynamic lift forces was implemented via cha nges of flow-rate, which was accomplished by a programmable pump. Several f low-rate gradients (step gradients, Linear gradients, parabolic, and combin ed gradients) were tested and evaluated as tools for optimization of the se paration of a silica gel particle mixture. The influence of increasing amou nt of sample injected on the peak resolution under flow-rate gradient condi tions was also investigated. This is the first time that flow-rate gradient s have been implemented for programming of the resulting force field acting on particles in GFFF. (C) 2001 Elsevier Science B.V. All rights reserved.