An electrochemical method for metal ion separations, called electrically switched ion exchange (ESIX), is described in this paper. In this method, direct oxidation and reduction of an electroactive film attached to an electrode surface is used to load and unload the film with alkali metal cations. The electroactive films under investigation are nickel hexacyanoferrates, which are deposited on the surface by applying an anodic potential to a nickel electrode in a solution containing the ferricyanide anion. Reported film preparation procedures have been modified to produce films with improved capacity and stability. Electrochemical behavior of the derivatized electrodes has been investigated with the use of cyclic voltammetry and chronocoulometry. The films show selectivity for cesium in concentrated sodium solutions. Raman spectroscopy has been used to directly monitor changes in the oxidation state of the film, and imaging experiments have demonstrated that the redox reactions are spatially homogeneous across the film. (C) 1997 Elsevier Science B.V.