Sensors and Actuators B 169 (2012) 96–105 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical j o ur nal homep a ge: www.elsevier.com/locate/snb Application of modified multiwall carbon nanotubes paste electrode for simultaneous voltammetric determination of morphine and diclofenac in biological and pharmaceutical samples Ali Mokhtari a,∗ , Hassan Karimi-Maleh b,∗ , Ali A. Ensafi c , Hadi Beitollahi d a Department of Engineering and Technology, Golestan University, Aliabad Katool, Iran b Department of Chemistry, Science and Research Branch, Islamic Azad University, Mazandaran, Iran c Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran d Environment Department, Research Institute of Environmental Sciences, International Center for Science, High Technology & Environmental Sciences, Kerman, Iran a r t i c l e i n f o Article history: Received 24 January 2012 Received in revised form 17 March 2012 Accepted 26 March 2012 Available online 1 April 2012 Keywords: Morphine and diclofenac Multiwall carbon nanotubes Vinylferrocene Voltammetric measurement a b s t r a c t A novel modified carbon paste electrode with vinylferrocene/multiwall carbon nanotubes was fabri- cated. The electrochemical response of the modified electrode toward morphine was studied by means of cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The structural morphology of the modified electrode was characterized by SEM technique. The pre- pared electrode showed an excellent electrocatalytic activity in the oxidation of morphine, leading to remarkable enhancements in the corresponding peak currents and lowering the peak potential. Using square wave voltammetry (SWV), we could measure morphine and diclofenac in one mixture inde- pendently from each other by a potential difference of about 300 mV for the first time. Square wave voltammetric peaks current of morphine and diclofenac increased linearly with their concentrations in the ranges of 0.2–250.0 mol L -1 , and 5.0–600.0 mol L -1 , respectively. The detection limits of 0.09 and 2.0 mol L -1 were achieved for morphine and diclofenac, respectively. The proposed voltammetric sensor was successfully applied to the determination of morphine and diclofenac in real samples. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Morphine, a phenolic compound is an alkaloid, which can cause disruption in the central nervous system, is frequently used to relieve severe pain in patients, especially that undergoing surgical procedure [1]. The purposes of morphine in biological samples are mainly monitor therapeutic levels in patients, drug concentrations in human and animal pharmacokinetic studies, investigation of opi- ate abuse for epidemiological purposes of drug abuse control as well as in forensic cases as an indicator of heroin usage and to identify causes of intoxication or death in cases of clinical and pathological interest [2]. To date, many analytical methods have been developed to determine of morphine concentrations, including high per- formance liquid chromatography [3,4], UV–Vis spectroscopy [5], gas chromatgraphy–mass spectroscopy [6,7], fluorimetry [8–11], chemiluminescence [12–14], surface plasma resonance (SPR) [15], and electrochemical methods [16–22]. Diclofenac, [o-(2,6-dichloroanilino)phenyl] acetate, is a rel- atively safe and effective non-steroidal drug with pronounced ∗ Corresponding authors. E-mail address: h.karimi.malh@gmail.com (H. Karimi-Maleh). anti-rheumatic, anti-inflammatory, analgesic and anti-pyretic properties [23], which is widely used in the treatment of degen- erative joint diseases and other arthritic conditions [24,25]. In view of the prominence of diclofenac in clinical applications, var- ious efforts have been made for the determination of diclofenac including gas chromatography–mass spectrometry [26,27], liq- uid chromatography [28–30] and liquid chromatography–tandem mass spectrometry [31], spectrophotometry [32–34], colorimetry [35], spectrofluorimetry [36] and voltammetry [37–40] in biologi- cal fluids. Non-steroidal anti-inflammatory drugs (such as diclofenac) have been shown to decrease morphine consumption after oper- ation in adults. The addition of regular doses of diclofenac may reduce the need for morphine after abdominal surgery [41]. There- fore, simultaneous determination of these drugs is very important. Carbon nanotubes (CNTs) have gained considerable atten- tion in recent years because of their remarkable electronic and mechanical properties [42,43]. The unique features of CNTs make them extremely attractive for a wide range of sensing applications [44,45]. The ability of CNTs-modified electrodes to promote electron-transfer reactions and resistance to surface foul- ing has been documented in connection to important biomolecules [46–51]. 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.03.059