Most of the ion sensors are a potentiometric device of a two-electrode system. The potentiometric device has disadvantages of potential drift and low reproducibility, and the calibration procedure is often required before the measurement. However, calibration is not suitable for point of care testing with a handy device by a non-expert person such as a customer. In the present work, we developed the thin layer electrolysis cell for the ion transfer at the liquid-liquid interface and applied it to the coulometric determination of a redox-inert ion, which works as a calibration-free ion sensor[1-4]. The thin layer electrolysis cell is a two-electrode system and has a laminate structure composed of the conducting polymer-coated electrode (CP-E), the organic thin layer membrane of 2-nitrophenyl octyl ether (NPOE, thickness of 30 μm), the aqueous thin layer solution (W, thickness of 50 μm) and an Ag/AgCl electrode (Figure 1 ).
We applied the thin layer electrolysis cell to the flow injection analysis of the redox-inert ion (Figure 1). The electrical charge of the current peak was converted to the mole amount through Faraday’s low. In the concentration range of 5-100 μM, the electrolysis efficiency, ε%, was close to 100%, which means that the flow injection analysis in the range realizes coulometric determination (calibration-free).
1. Y. Yoshida, S. Yamaguchi, K. Maeda, “Conducting polymer-coated electrode as a reference/counter electrode in an organic phase and its application to a two-electrode type thin-layer cell for voltammetry at the liquid | liquid interface”, Anal. Sci., 26, 137-139 (2010).
2. Y. Yoshida, S. Nakamura, J. Uchida, A. Hemmi and K. Maeda, “A flow electrolysis cell with a thin aqueous phase and a thin organic phase for the absolute determination of trace ionic species”, J. Electroanal. Chem., 707, 95-101, (2013).
3. Y. Yoshida, J. Uchida, S. Nakamura, S. Yamaguchi and K. Maeda, Analytical Sciences, Improved Thin-layer Electrolysis Cell for Ion Transfer at the Liquid|Liquid Interface Using a Conducting Polymer-coated Electrode, Anal. Sci., 30(3), 351-357 (2014).
4. E. Kusakabe, Y. Nakamura, K. Maeda, M. Fukuyama, Y. Yoshida, “Effect of oxidation ratio of conducting polymer on potential stability of the conducting polymer-coated electrode in voltammetric cell for the ion transfer”, J. Electroanal. Chem., 825, 8-15 (2018)