Electrocatalytic oxidation of hydrazine at o-aminophenol grafted modified glassy carbon electrode: Reusable hydrazine amperometric sensor Hossam M. Nassef a , Abd-Elgawad Radi a,c, * , Ciara K. O’Sullivan a,b, * a Nanobiotechnology and Bioanalysis Group, Department of Chemical Engineering, Universitat Rovira i Virgili, Avinguda Paisos Catalans 26, 43007 Tarragona, Spain b Institucio ´ Catalana de Recerca i Estudis Avanc ¸ ats, Passeig Lluı ´s Companys 23, 08010 Barcelona, Spain c Department of Chemistry, Faculty of Science, Mansoura University, 34517 Dumyat, Egypt Received 21 February 2006; received in revised form 4 May 2006; accepted 5 May 2006 Available online 21 June 2006 Abstract Here, we report a simple and extremely effective method to chemically grafting of o-aminophenol film (o-AP) onto glassy carbon (GC) electrode by the electrochemical reduction of the corresponding nitrophenyl diazonium salt in acidic aqueous solution for the electro- catalytic detection of hydrazine. The covalently attached o-AP enabled hydrazine to be catalytically oxidized at a greatly reduced over- potential and in a wide operational pH range. A quinoneimine structure has been proposed as the electrocatalytically active species. The kinetics of the reaction between the o-AP mediator and hydrazine has been characterized using cyclic voltammetry, chronoamperometry, and chronocoulometry and rotating disk electrode voltammetry. The o-AP modified electrode as an amperometric sensor has been char- acterized. The catalytic currents were proportional to the concentration of hydrazine giving rise to calibration curves characterized by two linear segments. The linear segment over the concentration range of 2.0–20.0 lM could be used with analytical purposes to deter- mination of hydrazine with a detection limit of 0.5 lM and a sensitivity of 0.016 lA/lM. The precision of amperometry was found to be 1.7% for replicate determinations (n = 10) of a 10 lM solution of hydrazine. The resulting modified electrode retains its initial response for at least one month if stored dry in air. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Electrocatalytic oxidation; Hydrazine; Diazonium salt; Surface modification; Hydrazine sensor 1. Introduction Hydrazine finds widespread usage in rocket fuels, missile systems, weapons of mass destruction and fuel cells [1]. In industrial applications, is also used as catalyst, emulsifier, corrosion inhibitor and reducing agent. It is also used as an oxygen scavenger in industry and has found wide appli- cation as an antioxidant, photographic developer and an insecticide [2]. Hydrazine has been recognized as a neuro- toxin, carcinogenic mutagenic and hepatotoxic substance, which affects liver and brain glutathione [3]. It is therefore obvious that reliable and sensitive analytical methods for the determination of hydrazine are needed. Numerous methods have been reported for the determination of trace amounts of hydrazine, including titrimetric [4], coulometric [5], potentiometric [6,7], spectrophotometric [8,9] and chro- matographic methods [10–12]. Electrochemical techniques offer the opportunity for portable, cheap and rapid methodologies. Much interest has centered on the use of carbon as an inexpensive sub- strate for electrochemical techniques. However, electro- chemical oxidation of hydrazine is kinetically sluggish 0022-0728/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2006.05.007 * Corresponding authors. Address: Nanobiotechnology and Bioanalysis Group, Department of Chemical Engineering, Universitat Rovira i Virgili, Avinguda Paisos Catalans 26, 43007 Tarragona, Spain. Tel.: +34 977 558740; fax: +34 977 559667. E-mail addresses: abd.radi@urv.net (A.-E. Radi), ckosulli@etse.urv.es, ciara.osullivan@urv.net (C.K. O’Sullivan). www.elsevier.com/locate/jelechem Journal of Electroanalytical Chemistry 592 (2006) 139–146 Journal of Electroanalytical Chemistry