Retention in continuous two-dimensional thermal field-flow fractionation: comparison of experimental results with theory
A theoretical and experimental study of continuous two-dimensional thermal field-flow fractionation (2D-ThFFF) is presented. Separation takes place in radial flow between two closely spaced discs, one of which is heated and the other cooled in order to maintain a temperature gradient across the channel. The cooled disc, which serves as the accumulation wall, is rotated relative to the other to create a shear component to the fluid flow. Under the influence of the thermal gradient and flow components, the sample components spiral outwards along different paths to the outer rim of the channel to be collected. The general principle of operation is described and an approximate theoretical model formulated for predicting the outlet position for the path of each sample component. The influence of the principal operational parameters, such as radial and angular flow rates and thermal gradient, on the deflection angle of the sample trajectory is investigated. Fractionation is demonstrated for polystyrene polymer standards in a binary solvent consisting of cyclohexane and ethylbenzene. Experimental results are compared with theoretical predictions.