SAGE-Hindawi Access to Research International Journal of Electrochemistry Volume 2011, Article ID 764294, 10 pages doi:10.4061/2011/764294 Research Article Voltammetric Determination of Acetaminophen in the Presence of Codeine and Ascorbic Acid at Layer-by-Layer MWCNT/Hydroquinone Sulfonic Acid-Overoxidized Polypyrrole Modified Glassy Carbon Electrode Saeed Shahrokhian 1, 2 and Reyhaneh-Sadat Saberi 1 1 Department of Chemistry, Sharif University of Technology, Tehran 11155-9516, Iran 2 Institute for Nanoscience and Technology, Sharif University of Technology, Tehran 11155-9516, Iran Correspondence should be addressed to Saeed Shahrokhian, shahrokhian@sharif.edu Received 26 March 2011; Revised 19 May 2011; Accepted 21 May 2011 Academic Editor: Farnoush Faridbod Copyright © 2011 S. Shahrokhian and R.-S. Saberi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A very sensitive electrochemical sensor constructed of a glassy carbon electrode modified with a layer-by-layer MWCNT/doped- overoxidized polypyrrole (oppy/MWCNT /GCE) was used for the determination of acetaminophen (AC) in the presence of codeine and ascorbic acid (AA). In comparison to the bare glassy carbon electrode, a considerable shift in the peak potential together with an increase in the peak current was observed for AC on the surface of oppy/MWCNT/GCE, which can be related to the enlarged microscopic surface area of the electrode. The effect of the experimental conditions on the electrode response, such as types of counter ion, pyrrole and counter ion concentration, potential and number of cycles in the polymerization procedure, amount of MWCNT, and the pH, were investigated. Under the optimized conditions, the calibration curve was obtained over two concentration ranges of 2 × 10 −7 –6 × 10 −6 M and 4 × 10 −5 –1 × 10 −4 M of AC with a linear correlation coefficient (R 2 ) of 0.9959 and 0.9947, respectively. The estimated detection limit (3σ ) for AC was obtained as 5 × 10 −8 M. The developed method was successfully applied to analyze the pharmaceutical preparations of AC, and a recovery of 95% with a relative standard deviation of 0.98% was obtained for AC. 1. Introduction The remarkable application potential of conducting poly- mers (CP) in chemical and biological sensors is one of the main reasons for the intensive investigation and development of the studies on these materials [1]. In the case of polypyr- role (ppy), useful features considered include its capacity to form adhesive coatings at different substrates, the possibility of growing it in aqueous media, easiness for chemical substi- tution to modify its properties, high porosity that enables fast kinetics of ion exchange with the surrounding medium, high electronic conductivity, high chemical stability, thickness controllability, ease of electrochemical polymerization, and good reversibility between its conducting and insulating states. These characteristics make ppy suitable in various electrochemical determinations including voltammetric and potentiometric [2], amperometric [3], and impedimetric [4, 5] techniques for the determination of various molecular species. Polypyrrole in its oxidized form is a positively charged conducting polymer. Upon the overoxidation process, it loses its conductivity and charge and instead, its porosity would be improved. Characterization of these films revealed that overoxidation results in addition of carbonyl and carboxyle groups to the structure of the conducting polymer. These groups attract cationic species and reciprocally reject negatively charged ones, for example, ascorbate anions [6]. Carbon nanotubes (CNT) are considered as a novel form of carbon materials in two past decades [7]. In the recent years, carbon nanotubes (CNTs) have also been incorporated into the electrochemical sensors. While they have many properties of the other types of carbon, they offer unique