Interval free flow zone electrophoresis is a new mode of free flow zone electrophoresis (FFZE), which facilitates purification of proteins and other molecular substances at very high resolution. It can be performed in the commercially available free flow electrophoresis (FFE) apparatus Octopus. The specimens are loaded and unloaded as usual with the help of a thin buffer film flowing between the two glass plates of the FFE. However, as long as electrical current is applied to a specimen, the medium flow is turned off and conditions of static column electrophoresis are simulated within the FFE device. Thereby electrohydrodynamic flow effects, which widen the sample bands migrating within the electric field, are eliminated while optimal heat removal from the thin buffer film is still possible and a sophisticated technique of harvesting of fractions remains available. Thus interval FFZE offers a gentle preparative method for purification of many kinds of charged molecular species such as proteins or dyes at very high resolution.