Enhancement of performance in sedimentation field-flow fractionation by temperature elevation

Nonequilibrium theory, combined with the principles of time optimization, show that the time necessary to achieve a given separation in FFF is scaled to eta/T, where eta is viscosity and T is absolute temperature. The eta/T ratio for water (and other common liquids) decreases several-fold for modest temperature gains of approximately 20-60 degrees C, implying a significant advantage for FFF operation at elevated temperatures. This concept was tested by modifying a standard sedimentation FFF apparatus with a heating system. The separation of 0.220-0.742 microns polystyrene latex beads in aqueous carrier liquids was compared at room temperature and at elevated temperatures of 51 and 68 degrees C. Both separation power and speed were improved. In accordance with the predicted eta/T scaling, the separation time of five bead sizes at a given resolution level was reduced by a factor of approximately 2.4 (from 29 to 12 min) in elevating the temperature from 25 to 68 degrees C. Some other potential benefits of temperature elevation in FFF are discussed.