Abstract: Apparatus for separating a mixture of particles comprising a chamber with an inlet and an outlet, means for providing an eluant flow between said inlet and said outlet, within the chamber an electrode structure of at least two electrodes, means for applying an alternating voltage between the electrodes, said electrode structure being such that when energized in operation of the apparatus there is established in the eluant a spatially non-uniform alternating field, whereby particles caused to flow through the chamber in said eluant flow are carried past the electrode structure and are separated into fractions. There may be an ancillary electrode structure of at least two electrodes placed upstream of the main electrode structure with regard to the direction of the flow of fluid. At least one of the electrodes of the electrode structure may be comprised of one or more grid like structures. The electrode structure may be comprised of interleaved grid like structures aligned to obstruct straight through flow.

Abstract: Dielectrophoretic collection rates of micro-organisms or other animate or inanimate dielectrically polarizable particles in suspension in a fluid are established by flowing the suspension past electrodes energized to produce a non-uniform alternating electric field in the suspension, terminating the energization of the electrodes after a predetermined time to release particles collected from the suspension, and, downstream of the electrodes, measuring the pulse of released particles as a measure of the rate of particle collection during energization of the electrodes. Repeated measurements at different field frequencies enable a collection-rate spectrum to be established and the particles under examination to be characterized or identified by reference to known spectra of known particles.