CONCENTRATION EFFECTS IN FIELD-FLOW FRACTIONATION WITH SECONDARY CHEMICAL-EQUILIBRIA

In field-flow fractionation with secondary chemical equilibria (SCE-FF F), small solutes can be separated according to their distribution coe fficient between a carrier additive species affected by the applied fi eld and the bulk carrier. Due to its interaction with the applied fiel d, the average additive concentration within the FFF channel is genera lly significantly larger than in the carrier reservoir and becomes so high that additive-additive interactions cannot be neglected. A recent retention model of FFF at finite concentrations is applied to SCE-FFF . In contradistinction with previous theories in which additive-additi ve interactions were not accounted for, it is found that the retention time of a given solute goes to a maximum when the additive concentrat ion in the carrier increases. Published SCE-FFF experimental data are examined in light of this model. The potential of this FFF operating m ode and guidelines for optimizing the separation are discussed.