Analytica Chimica Acta 730 (2012) 99–111 Contents lists available at SciVerse ScienceDirect Analytica Chimica Acta j ourna l ho me page: www.elsevier.com/locate/aca Construction and performance characteristics of new ion selective electrodes based on carbon nanotubes for determination of meclofenoxate hydrochloride Rasha M. El-Nashar ∗ , Nour T. Abdel Ghani, Sherif M. Hassan Chemistry Department, Faculty of Science, Cairo University, Giza, 12613, Egypt a r t i c l e i n f o Article history: Received 3 July 2011 Received in revised form 9 October 2011 Accepted 11 October 2011 Available online 15 November 2011 Keywords: Meclofenoxate Ion selective electrode Potentiometry Polyvinyl chloride membrane Carbon paste electrodes Carbon nanotube chemically modified carbon paste electrodes a b s t r a c t This work offers construction and comparative evaluation the performance characteristics of conven- tional polymer (I), carbon paste (II) and carbon nanotubes chemically modified carbon paste ion selective electrodes (III) for meclofenoxate hydrochloride are described. These electrodes depend mainly on the incorporation of the ion pair of meclofenoxate hydrochloride with phosphomolybdic acid (PMA) or phosphotungestic acid (PTA). They showed near Nernestian responses over usable concentration range 1.0 × 10 -5 to 1.0 × 10 -2 M with slopes in the range 55.15–59.74 mV (concentration decade) -1 . These developed electrodes were fully characterized in terms of their composition, response time, working concentration range, life span, usable pH and temperature range. The electrodes showed a very good selectivity for Meclo with respect to a large number of inorganic cations, sugars and in the presence of the degradation product of the drug (p-chloro phenoxy acetic acid). The standard additions method was applied to the determination of MecloCl in pure solution, pharmaceutical preparations and biological samples. Dissolution testing was also applied using the proposed sensors. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Meclofenoxate hydrochloride (MecloCl) [CAS number 51-68-3] is [(4-chlorophenoxy)-acetic acid 2-(dimethylamino) ethyl ester hydrochloride] of molecular formula C 12 H 16 ClNO 3 ·HCl and molec- ular weight 294.18 g moL -1 and it has the structure shown in Scheme 1. Meclofenoxate is a one of the older nootropic drugs used to treat the symptoms of senile dementia and Alzheimer’s disease. Several different methods have been used for the determination of MecloCl including high performance liquid chromatography (HPLC) [1–4], capillary electrophoresis [5], resonance Rayleigh scattering method [6] and proton magnetic resonance method [7]. One potentiometric method [8] has been reported for the determination of meclofenox- ate. Nanomaterials have received great attention in recent years in different fields due to their enormous potential. Among them, car- bon nanotubes (CNTs) have attracted significant interest due to their extraordinary electrical, chemical, mechanical and structural properties [9] that make them very attractive for diverse applica- tions such as nanoelectronics and sensors [10,11]. The advantages of both single-wall (SW) and multi-wall (MW) CNTs, such as high surface area, good conductance, favorable electronic properties and ∗ Corresponding author. E-mail address: rasha.elnashar@guc.edu.eg (R.M. El-Nashar). electrocatalytic effect make them adequate for the construction of electrochemical sensors and biosensors [12,13]. The incorporation of electroactive materials into a carbon nanotubes paste electrode is advantageous and has been widely applied in the electroanalyt- ical community [14]. Carbon nanotubes working electrodes have been proved beneficial helping the electron exchange reaction in redox processes of different species. The results reported by vari- ous researchers suggest that CNT can be used to improve electrons transfer reactions of many desired molecules [15,16]. In the present work, plastic membrane, a carbon paste and carbon nanotube chemically modified carbon paste electrodes for meclofenoxate cation were constructed and the performance char- acteristics were studied. The electrodes were used to determine MecloCl in pure solutions, pharmaceutical preparations and bio- logical samples including urine and plasma. 2. Experimental 2.1. Reagents and materials All the chemicals used were of analytical grade. Bi-distilled water was used throughout all experiments. Pure-grade meclofenoxate hydrochloride was provided by Mina Pharmaceu- tical Co., Egypt, while its pharmaceutical preparations (Lucidril ® 250 mg and Lucidril ® 500 mg) are purchased from local mar- ket. Phosphotungstic acid (PTA), phosphomolybdic acid (PMA), tetrahydrofuran (THF), dioctylphthalate (DOP), dioctyladipate 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.10.069