Concentration and Analysis of Dilute Colloidal Samples by Sedimentation Field-Flow Fractionation

An on-channel concentration procedure is described in which large volumes of dilute colloidal materials can be concentrated at the head of an FFF channel in preparation for separation and analysis. The theory of the procedure is described, with particular focus on expected perturbations in retention and plate height due to the finite initial zone length. Two sizes (0.357 and 0.481 μm) of polystyrene latex beads diluted in volumes of up to 50 ml are used as model colloids. Separation of the two bead sizes is demonstrated. The beads are then subjected to careful retention and plate height measurements and the results compared to theoretical expectations. Certain anomalies are noted which may relate to the reversible adhesion of the particles to the channel wall. Possible extensions and ramifications of the technique are noted.