Complete Electrolysis Using a Microflow Cell with an Oil/Water Interface Shigeo Sawada, † Masaru Taguma, ‡ Takashi Kimoto, ‡ Hiroki Hotta, § and Toshiyuki Osakai* ,§ Department of Chemistry, Faculty of Science and Engineering, Kinki University, Higashiosaka, Osaka 577-8502, Japan, Kimoto Electric Company, Ltd., 3-1 Funahashi-cho, Tennoji, Osaka 543-0024, Japan, and Department of Chemistry, Faculty of Science, Kobe University, Nada, Kobe 657-8501, Japan A novel microflow cell with a nitrobenzene (NB)/ water (W) interface was developed. A poly(tetrafluoroethylene) mem- brane filter was employed to prepare the NB/ W interface which was formed over a thin channel (0.1 mm thick, 48 cm long) on a silver plate. The silver plate was electrolyzed in advance and served as an Ag/ AgCl electrode for controlling the Galvani potential difference across the NB/ W interface as well as detecting the current flowing through the interface. Using the microflow cell, complete electrolysis was accomplished for the interfacial transfer of a representative ion (i.e., tetramethylammonium ion). Thus, the present microflow cell was shown to be promis- ing for coulometric (i.e., absolute quantitative) analysis of ions. Also, the microflow cell was shown to be useful for determination of the number of electrons for compli- cated charge-transfer processes at the oil/ water interface. In recent years, much attention has been paid to amperometric (or voltammetric) detection of ions with a liquid/ liquid interface or an oil/ water (O/ W) interface. 1-4 The amperometric detection is based on measurement of ion-transfer current, which is directly proportional to ion concentration and is therefore very suitable for flow injection analysis (FIA). So far, a variety of amperometric flow cells with the O/ W interface have been reported. 5-12 However, they are all designed to detect ion-transfer current due to partial electrolysis of the sample aqueous solution. To the best of our knowledge, there has been reported no O/ W-type flow cell that can accomplish complete electrolysis 13 of the sample solution. If such a flow cell is realized, it will enable us to perform coulometric analysis of ions in a manner similar to conventional flow column electrodes utilizing glassy carbon granules or carbon fiber. 14,15 In this study, we constructed a microflow cell 16,17 using the hydrophobic membrane-stabilized O/ W interface, 18 which is formed over a thin channel (0.1 mm thick, 48 cm long) on a silver plate. By using the microflow cell, we have accomplished complete electrolysis for the interfacial transfer of a representative ion (tetramethylammonium ion, 19 TMA + ). Also, it has been shown that the microflow cell is promising for determination of the number of electrons for heterogeneous electron-transfer reac- tions 20,21 at the O/ W interface. EXPERIMENTAL SECTION Chemicals. Tetrabutylammonium tetraphenylborate 19 (TBAT- PB) and tetrapentylammonium tetraphenylborate 22 (TPnATPB) were prepared as described previously. Analytical grade tetrabu- tylammonium chloride (TBACl) or tetrapentylammonium chloride (TPnACl) was occasionally contaminated by a trace amount of * Corresponding author: (e-mail) osakai@ kobe-u.ac.jp. † Kinki University. ‡ Kimoto Electric Co., Ltd. § Kobe University. (1) Senda, M.; Osakai, T.; Kakutani, T.; Kakiuchi, T. Nippon Kagaku Kaishi 1986 , 956-964. (2) Senda, M.; Kakiuchi, T.; Osakai, T. Electrochim. Acta 1991 , 36, 253-262. (3) Senda, M.; Yamamoto, Y. In Liquid-Liquid Interfaces, Theory and Methods; Volkov, A. G., Deamer, D. W., Eds.; CRC Press: Boca Raton, FL, 1996; Chapter 12. (4) Reymond, F.; Fermı ´n, D.; Lee, H. 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