On the Focusing Mechanism in Thermal Field-Flow Fractionation of Macromolecules

The potential of separation of the macromolecules in solution by focusing thermal field-flow fractionation is critically analyzed. The experimental conditions of the high-performance separations of particulate species by this technique were extensively studied in the past and are well determined. On the other hand, very scarce and contradictory knowledge exists on the effective use of focusing thermal field-flow fractionation for the separation of macromolecules in solution. An important requirement is to apply the sufficient relaxation time to establish the initial steady-state distribution of the sample across the separation channel thickness, as close to the accumulation wall as possible, otherwise a serious zone broadening and false retention may occur. The concentration of the fractionated sample solution should be minimal, but allowing an accurate detector response, to avoid the viscous fingering and Rayleigh–Taylor hydrodynamic instabilities, and it should not exceed the critical concentration at which the macromolecular chains begin to overlap. The important conditions which enable or limit such separations are discussed.