Abstract: Improved apparatus and procedures for electrical field-flow fractionation is disclosed. A test sample is injected into the liquid carrier stream flowing through the flow channel of the apparatus. The apparatus comprises a thin flow channel having a top, a bottom, and two side walls, with a fluid carrier inlet at one end and an outlet at the other end. The top and bottom walls are formed such that at least the inner surfaces thereof that face the flow channel are made of an electrically conductive material so that the inner surfaces thereof form electrodes as well as opposite, broad boundary surfaces of the flow channel. A voltage differential is applied to the electrically conductive inner surfaces of the top and bottom walls. The carrier fluid flowing through the channel can be deionized or distilled water as well as water containing a red-ox couple such as quinone/hydroquinone.