A novel liquid-junction-removed reference electrode system was developed for simultaneous multiplex amperometry using a closed bipolar electrode. The liquid junction between the reference cell and the sample cell was replaced by a bipolar electrode to ensure electron conductivity in lieu of ionic conductivity in conventional systems. Under the condition where the redox reaction of the analyte at the bipolar electrode in the sample cell was a limiting process, voltammetric and amperometric measurements were performed for quantitative detection of the analytes. After characterization of the system, a chip-type device was fabricated with six sample cells and one reference cell. Simultaneous determination of ferrocene methanol was conducted in six solutions in the 0.1–0.5 mM range. This is the first demonstration of the simultaneous multiplex determination of analytes with a liquid-junction-removed system. Although the potential control problem (which is different to the liquid potential problem of conventional liquid junction) still remains because of the increase of the solid–liquid interface, this system is expected to solve some problems associated with the liquid junction of the reference electrode, including sample contamination by chloride ions and the complicated process of fabricating a reference electrode on a chip.
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