Field-Flow Fractionation (FFF) as an Integral Experiment in Junior Physical Chemistry Labs

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This project incorporates field-flow fractionation (FFF) into the physical chemistry laboratory. This relatively new technique is rapidly gaining acceptance as a method for separating and characterizing macromolecules and particles with diameters ranging from 0.002 to 100 micrometers in diameter. The method is superficially similar to chromatography, but the basis of separation in FFF is the interaction of particle flow down a channel with an external field applied perpendicular to the direction of flow. Separation occurs because particles differ in their tendency to be forced into slow carrier streamlines adjacent to the channel wall. Besides being a new and promising technique, FFF is an ideal vehicle for introducing students to an experimental investigation of transport properties. For example, in normal mode flow FFF, the retention time of an eluted particle depends on the diffusion constant of that particle. Diffusion measurements have been made for macromolecules and other particles over the wide range of 0.002 to 1 micrometer. This project adopts FFF diffusion constant measurement as the primary nonequilibrium component of the junior-level physical chemistry laboratory. It joins experiments that characterize porous solids, measure activity coefficients electrochemically, ascertain enthalpies of combustion or solution, and establish rate constants of chemical reactions. Addition of the proposed FFF experiment also complements these exercises with one that is computer controlled. *