PRESSURE FIELD-FLOW FRACTIONATION OR POLARIZATION CHROMATOGRAPHY

When a pressurized fluid mixture flows past a reverse osmosis or ultra-filtration membrane the components of the mixture diffuse to, and permeate the membrane, at different rates and the extent to which a component is polarized at the membrane surface depends on its wall Peclet number, Pwi. Pressure field flow chromatography utilizes this phenomenon, and the resulting differential retardation (or increase in residence time) of the polarized solute particles in the slower moving concentrated fluid layers immediately adjacent to the membrane creates a chromatographic separation of the components of the mixture. The results of the present analysis of separation by pressure field flow fractionation (PFFF) between flat, narrowly spaced membranes are compared with those in a tube and with those obtained when a cross-flow in one membrane and out the other (flow field flow fraction) exists. The results suggest that all three approaches appear to have reasonably good potential for practical applications. Perturbation results for the large time values of Ki in the generalized dispersion equation, valid for large and small values of the parameter Pew are given in convenient algebraic forms for PFFF. For large values of Pew, solute retardation is very pronounced and axial dispersion is reduced very substantially, both of which suggest potentially favorable separations. A significant difference between PFFF and FFFF system is the exponential increase in Cm caused by the loss of carrier fluid along the conduit in the case of PFFF. The effect is reflected in the value of Ko. © 1979.