Closed bipolar electrode system for a liquid-junction-free reference electrode integrated in an amperometric probe sensor

Reference electrodes (REs) play an essential role in electrochemical measurements. REs require liquid junctions to allow for ion conductivity between the RE and the sample solution. However, a liquid junction causes unwanted ion leakage into the analyte and clogging inducing reference potential inaccuracy. In this study, we report a liquid-junction-free amperometric probe sensor with an integrated RE, based on a closed bipolar electrode (cBPE) system. The liquid junction of the RE was replaced by the cBPE, which provides electrical conductivity instead of ionic conductivity between the inner solution of the RE and the sample solution. Since the solutions were in two separate cells, undesired contamination was completely prevented. We successfully conducted voltammetric and amperometric quantitative detection of 0.1–0.5 mM ferrocenemethanol using this system. Although its uses are limited, the present probe sensor with integrated liquid-junction-free reference electrode provides a feasible alternative for amperometric electrochemical measurements.