ENHANCEMENT OF PERFORMANCE IN SEDIMENTATION FIELD-FLOW FRACTIONATION BY TEMPERATURE ELEVATION

Nonequilibrium theory, combined with the principles of time optimizati on, 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 temperatu re. The eta/T ratio for water (and other common liquids) decreases sev eral-fold for modest temperature gains of similar to 20-60 degrees C, implying a significant advantage for FFF operation at elevated tempera tures. This concept was tested by modifying a standard sedimentation F FF apparatus with a heating system. The separation of 0.220-0.742 mu m polystyrene latex beads in aqueous carrier liquids was compared at ro om temperature and at elevated temperatures of 51 and 68 degrees C. Bo th separation power and speed were improved. In accordance with the pr edicted eta/T scaling, the separation time of five bead sizes at a giv en resolution level was reduced by a factor of similar to 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 discusse d.