Electrocatalytic oxidation of thiosulfate at 2,7-bis(ferrocenylethyl)-fluoren-9-one-modified carbon paste electrode (2,7-BFEFMCPE): Application to the catalytic determination of thiosulfate in real sample Jahan Bakhsh Raoof * , Reza Ojani, Hassan Karimi-Maleh Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran Received 7 April 2010 Abstract Electrocatalytic oxidation of thiosulfate at the 2,7-BFEFMCPE occurs at a potential about 460 mV less positive than that unmodified carbon paste electrode. The diffusion coefficient (=5.6  10 5 cm 2 s 1 ), the kinetic parameters such as electron transfer coefficient, (=0.5) and k h (=1.21  10 3 cm s 1 ) of thiosulfate oxidation at the surface of, 2,7-BFEFMCPE were determined. The electrocatalytic oxidation peak current of thiosulfate showed two linear dynamic ranges (0.0006–0.009 mmol/L and 0.009– 0.900 mmol/L) and a detection limit of 0.00015 mmol/L. This method was also examined as a new electrochemical sensor for the determination of thiosulfate in real sample. # 2010 Jahan Bakhsh Raoof. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: 2,7-Bis(ferrocenylethyl)-fluoren-9-one; Thiosulfate; Electrocatalysis; Cyclic voltammetry; Differential pulse voltammetry The detection of thiol-derivative substances is an important field of research as they can be present as contaminants in fuels [1], act as physiological indicators in biological fluids. Also they were used as markers of food deterioration [2]. Therefore measurement of this kind of materials seems to be very important. Chemically modified electrodes (CMEs) are one of the methods which applied nowadays for measurement of this material that attracted scholarly attentions in last decade [3]. Various methods have been used for the immobilization of electroactive materials in the fabrication of CMEs. These methods include adsorption [4], covalent bonding [5], and immobilization of electroactive materials as a doping in a conducting polymer matrix [6] and so on. Sodium thiosulfate (Na 2 S 2 O 3 ) is a colorless crystalline compound that is more familiar as the pentahydrate, Na 2 S 2 O 3 5H 2 O [7]. Thiosulfate occurs naturally in hot springs and geysers, and is produced by certain biochemical processes. In the body, thiosulfate converts small amounts of cyanide ion into harmless products and plays a role in the biosynthesis of cysteine, a sulfur-containing amino acid that locks proteins into their correct three-dimensional shapes. Thiosulfate is not found in large quantities in nature. It is routinely used as a titrant to determine concentrations of www.elsevier.com/locate/cclet Available online at www.sciencedirect.com Chinese Chemical Letters 21 (2010) 1462–1466 * Corresponding author. E-mail address: j.raoof@umz.ac.ir (J.B. Raoof). 1001-8417/$ – see front matter # 2010 Jahan Bakhsh Raoof. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2010.06.004