1132 ISSN 1023-1935, Russian Journal of Electrochemistry, 2018, Vol. 54, No. 12, pp. 1132–1140. © Pleiades Publishing, Ltd., 2018. Published in Russian in Elektrokhimiya, 2018, Vol. 54, No. 12, pp. 1076–1085. TiO 2 /Fe 3 O 4 /Multiwalled Carbon Nanotubes Nanocomposite as Sensing Platform for Simultaneous Determination of Morphine and Diclofenac at a Carbon Paste Electrode 1 Ebrahim Dasht Razmi a , Hadi Beitollahi b, *, Masoud Torkzadeh Mahani c , and Marzieh Anjomshoa c a Department of Chemistry, Graduate University of Advanced Technology, Kerman, Iran b Environment Department, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran c Department of Biotechnology, Institute of Science, High Technology and Environmental Science, Graduate University of Advanced Technology, Kerman, Iran *e-mail: h.beitollahi@yahoo.com Received June 5, 2016; in final form, November 17, 2016 Abstract—A nanocomposite of TiO 2 /Fe 3 O 4 /MWCNTs (TFMWCNT) and ionic liquid was used to fabrica- tion of a novel modified carbon paste electrode. The modified electrode was used for voltammetric determina- tion of morphine. The proposed method exhibited wide linear dynamic range of 2.5 × 10 –8 to 6.0 × 10 –4 M with a detection limit (S/N = 3) of 1.5 × 10 –8 M for morphine. Also, the diffusion coefficient (D = 2.83 × 10 –6 cm 2 /s) and electron transfer coefficient (α = 0.31) for morphine oxidation were also determined. The novel sensor was used for simultaneous determination of morphine and diclofenac using square wave voltammetry (SWV). Finally this method was used for determination of morphine and diclofenac in some real samples. Keywords: morphine, diclofenac, TiO 2 /Fe 3 O 4 /MWCNTs nanocomposite, ionic liquid, drug analysis DOI: 10.1134/S1023193518140057 INTRODUCTION Morphine is most frequently used as an analgesic drug for short-term treatment of postsurgical, trau- matic pain and antitussive as well as for long-term treatment of severe pain in cancer patients [1, 2]. Though morphine is a powerful analgesic, but severe side effects, such as respiratory depression and sei- zures, are often occurring in patients. Therefore its use is rather questionable [3, 4]. The World Health Orga- nization (WHO) currently proposes a three-stage approach to the treatment of chronic pain associated with cancer; in which opioids including morphine are used in combination with nonsteroidal anti-inflam- matory drugs (NSAIDs). Generally, there is a consen- sus that diclofenac or some of the newer NSAIDs in combination with opiates increase analgesia and reduce adverse effects more than just increasing the dose of morphine alone [5–7]. Diclofenac is considered as one of the most effec- tive NSAIDs with strong anti-pyretic, analgesic and anti-inflammatory properties. Diclofenac is used to treat mild to moderate pain, or signs and symptoms of osteoarthritis or rheumatoid arthritis [8, 9]. On the other hand, although pharmacokinetic interactions between morphine and diclofenac cannot be neglected, only limited knowledge is available [10]. This might be caused by the lack of a simple and sen- sitive method for the simultaneous determination of morphine and diclofenac. To date, several analytical methods have been developed for the simultaneous determination of these drugs, including high perfor- mance liquid chromatography, gas chromatography– mass spectroscopy, fluorimetry, surface plasma reso- nance, chemiluminescence, capillary electrophoresis, radioimmunoassay and electrochemical methods [11–14]. In view of the above considerations drug analysis have played a vital role in drug quality control [15–17]. Hence, a simple, fast, selective, sensitive and accurate method for the determination of drugs is very import- ant. Electroanalytical methods have been more attrac- tive in recent years because they are fast, simple, power efficient, inexpensive, accurate and highly sen- sitive [18–21]. After developing the carbon paste electrode (CPE) by Adams in 1958, it has been used as an appropriate bed for electro-oxidation of various substances [22‒26]. The ease and speed of preparation, the creation of a new reproducible surface, low background current, wide range of potential application of carbon paste are some 1 The article is published in the original.