Multicompartment electrolyzers with isoelec. Immobiline membranes are used for large-scale preparative protein purifn. A series of isoelec. membranes, of defined pI values, is utilized for keeping any desired species isoelec. within each compartment of the electrolyzer. It is preferable to have electrode disks of the same surface area as the membranes for a proper performance of the instrument because electrolyte solns. of low cond. are used. The use of Pt disks would be quite expensive; therefore it is proposed using Zr as a cathode and Ti/IrO2 as an anode in the electrode compartments. This pairing of electrodes seems to give the same performance as Pt wires. Also, conventional isoelec. focusing, as well as isoelec. focusing in immobilized pH gradients, both requiring a good contact area between gel and electrodes, would benefit by using flat laminae of these metals as electrodes. [on SciFinder (R)]