A parallel multicompartmental electrolyzer recently developed for preparative-scale isoelectric trapping separations, trapping by recursive electrophoresis in a compartmentalized system, was set up to operate as a cascade of binary separations to produce at least one pure target ampholyte (or more, with additional separation heads) without other ampholytes ever entering (even transiently) the harvest stream. This mode of operation avoids the need for exhaustive electrophoresis and the accompanying long separation times brought about by the exponentially decreasing concentrations over the course of batch separations. Continuous operation can be achieved in the cascade mode by continuously feeding the sample into the first separation head configured with three flow-through compartments and continuously harvesting one (or more) target components in additional separation heads configured with two flow-through compartments, attached to the respective branching points.