Ž . Electrochemistry Communications 2 2000 782–785 www.elsevier.nlrlocaterelecom Amperometric determination of ascorbic acid at a ferricyanide-doped Tosflex-modified electrode Jyh-Myng Zen ) , Dong-Mung Tsai, Annamalai Senthil Kumar, Venkataraman Dharuman Department of Chemistry, National Chung-Hsing UniÕersity, Taichung 402, Taiwan, ROC Received 14 August 2000; received in revised form 1 September 2000; accepted 5 September 2000 Abstract Tosflex, a perfluoro-anionic exchange membrane, is not studied as much as Nafion for electroanalytical applications. In this study, Ž . electrocatalytic oxidation of ascorbic acid AA was demonstrated using a ferricyanide-doped Tosflex-modified electrode in pH 5 phosphate buffer solution. The modified electrode showed good stability over the studied pH range of 2–12. The electrocatalytic Ž . oxidation of AA on the modified electrode follows the surface-saturation kinetics in terms of Michaelis-Menten MM mechanism. The analytical estimations were performed amperometrically under hydrodynamic conditions at an applied potential of 300 mV versus AgrAgCl. A linear response was observed in the range of 0–50 mM with a regression coefficient of 0.998. q 2000 Published by Elsevier Science S.A. Ž . 3yr4y Keywords: Tosflex; Fe CN ; Ascorbic acid; Mediated oxidation 6 1. Introduction The development of amperometric sensors for the deter- Ž . mination of ascorbic acid AA , i.e., vitamin C, is impor- tant because of its crucial role in neurochemistry and w x industrial applications 1,2 . Several techniques were re- ported for AA determination including spectroscopic, chro- w matographic, enzymatic and electroanalytical methods 2– x 5 . Compared to other options, electroanalysis has the advantages of simplicity and high sensitivity. Ferricyanide was proved an effective redox mediator for AA oxidation in homogeneous solution phase as well as in polymer w x matrix 6–10 . We report here the application of the ferri- Ž . cyanide-doped Tosflex-modified electrode FDTME for the detection of AA. Tosflex, a new class of perfluorinated polycationic polymer, was considered as a suitable alter- Ž .Ž . w x nate for poly 4-vinlylpyridine PVP 11,12 and rarely w x studied in electrochemical applications 13,14 . For com- parison, the activity of the ferricyanide-doped PVP-mod- Ž . ified electrode FDPME was also investigated. The FDTME was proved to possess an excellent mediated activity for AA over a wide pH range compared to the FDPME. The reaction was found to follow the surface ) Corresponding author. Fax: 886-4-2862547. Ž . E-mail address: jmzen@dragon.nchu.edu.tw J.-M. Zen . saturation kinetics similar to the enzymatic catalytic reac- tion. 2. Experimental 2.1. Reagents Ž . The Tosflex membrane IE-SA 48 was obtained from Tosoh Soda, Japan. Ascorbic acid and PVP were obtained from Aldrich. All the other compounds used in this work were prepared from ACS-certified regent grade chemicals without further purification and dissolved in doubly dis- tilled deionized water. Unless otherwise noted, a 0.1 M, Ž . pH 5 phosphate buffer solution PBS was used for all electrochemical measurements. 2.2. Apparatus Voltammetric measurements were carried out with CHI Ž Model 660 electrochemical workstation CH instruments, . Austin, TX, USA . The three-electrode system consists of one of the flowing working electrode: GCE, FDTME or Ž . FDPME, an AgrAgCl reference Model RE-5, BAS and a platinum auxiliary electrode. 1388-2481r00r$ - see front matter q 2000 Published by Elsevier Science S.A. Ž . PII: S1388-2481 00 00121-1