This paper describes the development of an annular chamber designed for preparative free-flow electrophoresis which can operate at voltages up to 20 kV, electric fields up to 65 kV/m, and power densities as high as 10 MW/m(3). This apparatus uses counter-rotating fluid vortices to stabilize the aqueous medium in the annulus against natural convection while improving heat and mass transfer over vortex-free Couette flow. The vortices are generated by rotating the inner surface of the annulus and, if the rotor and stator have complementary shapes, dispersion induced by electrokinetic and electrohydrodynamic flows can be mitigated even at the highest operating voltages. Following a brief overview of contemporary annular free-flow instrumentation, the theoretical principles for momentum and heat transport in the vortices are discussed in some detail and then the results of several electrofocusing experiments are provided to illustrate the resolving power of this instrument.