Particle retention and ionic strength effects in thermel field-flow fractionation

Abstract

Field-Flow Fractionation (FFF) of which thermal field-flow fractionation (ThFFF) is a member of, is a family of separation techniques applicable to the separation of macromolecules and particles. FFF spans a wide mass/size range in which sample components are subjected to the combined effects of (1) an external field (or gradient) applied perpendicular to the axis of a narrow ribbon-like channel structure and (2) the axial flow of a carrier liquid flowing through an open channel. Separation of sample components occurs when different sample populations are selectively driven into different flow laminae of the nearly parabolic flow profile by the external field. In ThFFF, the external "field" is an intense temperature gradient applied across the channel enclosed between two parallel, highly polished metal bars. As a result of thermal diffusion, macromolecular and particulate components in a carrier liquid are forced differentially toward one wall of the channel, leading to separation. In this work, the efficacy of ThFFF to retain and separate standard polystyrene particles according to size in an aqueous media is reported. A comprehensive empirical study of perturbations to particle retention and separation arising from ionic strength adjustments of the aqueous carrier stream using a chemically neutral salt is provided and discussed. The perturbations are reported and discussed in terms of the effects of salt concentration on parameters such as particle retention and elution time, resolution between different particle sizes, sample recovery, and channel efficiency. The perturbations on particle behaviour in the ThFFF are attributed to particle-wall electrostatic and VanDer Waals interactions. The combined effects of carrier ionic strength, applied field strength and channel flow rate on the general operation and performance of the FFF separation technique are also given. The results show that increases in the salt concentration of the carrier stream