Application of a Carbon-Paste Electrode Modified with 2,7- Bis(ferrocenyl ethyl)fluoren-9-one and Carbon Nanotubes for Voltammetric Determination of Levodopa in the Presence of Uric Acid and Folic Acid Hadi Beitollahi,* a Jahan-Bakhsh Raoof , b Rahman Hosseinzadeh c a Environmet Department, Research Institute of Environmental Sciences, International Center for Science, High Technology & Environmental Sciences, Kerman, Iran phone: 00983426226613; fax: 00983426226617 b Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry,University of Mazandaran, Babolsar, Iran c Department of Organic Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran *e-mail: h.beitollahi@yahoo.com Received: May 4, 2011; & Accepted: May 18, 2011 Abstract A carbon-paste electrode modified with 2,7-bis(ferrocenyl ethyl)fluoren-9-one and carbon nanotubes was used for the sensitive voltammetric determination of levodopa (LD). The electrochemical response characteristics of the modified electrode toward LD, uric acid (UA) and folic acid (FA) were investigated. The results showed an efficient catalytic activity of the electrode for the electrooxidation of LD, which leads to lowering its overpotential by more than 320 mV. The modified electrode exhibits an efficient electron mediating behavior together with well-separated oxidation peaks for LD, UA and FA. Also, the modified electrode was used for determination of LD in some real samples. Keywords: Levodopa, Uric acid, Folic acid, Carbon nanotubes, Modified electrode, Electrocatalysis DOI: 10.1002/elan.201100242 1 Introduction Nanomaterials have received great attention in recent years in different fields due to their enormous potential. Among them, carbon nanotubes (CNTs) have become the subject of intense investigation since their discovery in 1991 by Iijima [1]. Such considerable interest reflects the unique behavior of CNTs, including their remarkable electrical, chemical, mechanical and structural properties that make them a very attractive material for a wide range of applications [2,3]. The advantages of both single-wall (SW) and multiwall (MW) CNTs, such as high surface area, good conductance, favorable electronic properties and electrocatalytic effect make them ade- quate for the construction of electrochemical sensors and biosensors [4]. The incorporation of electroactive materi- als into a carbon nanotubes paste electrode is advanta- geous and has been widely applied in the electroanalyti- cal community [5–10]. Parkinson)s disease (PD) is believed to be related to low levels of dopamine (DA) in certain parts of the brain. LD is considered the most effective treatment available for Parkinson)s disease. When LD is taken orally, it crosses through the ((blood–brain barrier”. Once it crosses, it is converted to DA. The resulting increase in brain DA concentrations is believed to improve nerve conduction and assist the movement disorders in PD. Therefore the success of DA replacement therapy by its precursor, LD, is a major landmark in the field of neurol- ogy. Chronic LD treatment in PD patients is frequently associated with some side effects such as nausea and vom- iting results from the increases of plasma LD level. Clear- ly the process of LD detection and its concentration de- termination is an important feature in pharmaceutical and clinical procedures [11, 12]. Several methods for the determination of LD have been described in literature including high performance liquid chromatography (HPLC) [13], flow injection system [14] and capillary zone electrophoresis [15, 16]. Beside the fact that the methods based on electrochemi- cal sensors have many advantages over the other meth- ods, there are few papers on the determination of LD in pharmaceutical formulations using the modified electro- des [17–20]. Uric acid (UA) is the end product of catabolism of the purine nucleosides [21]. Most of UA produced from the catabolism is reabsorbed into the blood circulation system after primary filtration and partial secretion by 1934 # 2011 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Electroanalysis 2011, 23, No. 8, 1934 – 1940 Full Paper