Development of on-line concentration methods in flow field-flow fractionation

Field-flow fractionation (FFF) is a family of elution-based separation and characterization techniques that utilize an external field to induce differential retention of macromolecular and particulate species. In flow FFF, the retention of the species is controlled by a crossflow of carrier liquid directed perpendicular to the channel flow axis. Permeable walls must be used to accommodate the crossflow of fluid. This physical feature of the channel allowed the development of the opposed-flow sample concentration (OFSC) method for the analysis of dilute sample suspensions or solutions.; This dissertation discusses the implementation and optimization of this novel on-line concentration procedure for introducing large volumes of dilute sample suspensions into a flow FFF channel. The technique requires only a simple change in the fluid flow paths within a standard flow FFF system for the period required for sample concentration. The concentration process, which consists of sample loading, focusing and flow stabilization stages, was optimized with respect to time. The reliability of the technique was tested by measuring the recovery and reproducibility of model environmental colloids, polystyrene latex beads, and proteins. The original sample suspensions (10-1000 mL volume) were concentrated 1000-100,000 times in the flow FFF channel which has a 1 mL void volume.; As an example of an application to a real world sample, the technique was applied to the analysis of river colloids. The optimum experimental conditions for river colloids was obtained via recovery studies.; Sedimentation FFF and flow FFF using the concentration method were linked together for analysis of model colloids. Four sample loading methods in the concentration run were compared at the same concentration time. The concentration run in asymmetrical flow FFF was achieved based on a new experimental procedure. In addition, a new method for measuring void volume was derived theoretically.