ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2010, том 65, № 10, с. 1075–1083 1075 Dextromethorphan (3-methoxy-17-methylmorphi- nan monohydrate), Fig. 1, is the d-isomer of levorpha- nol, a codeine analog. Dextromethorphan is used world- wide as an antitussive agent in cough and cold medica- tions in at least 125 products. Because of its ready accessibility, recreational abuse of dextromethorphan has been increasing in recent years, although accurate statis- tics are not available [1]. Different methods have been reported for the de- termination of dextromethorphan in products and bi- ological samples such as high performance liquid chromatography (HPLC) [2], the first and second-de- rivative technique UV spectrophotometry [3], capil- lary electrophoresis [4], gas chromatography (GC) [5], liquid chromatography (LC) [6] and thin layer chro- matography (TLC) [7]. Potentiometric sensors are playing an important role in pharmaceutical analysis [8–10] because of their sim- plicity, rapidity and accuracy over some other analytical methods like spectrophotometry and HPLC. Also, other mentioned methods are elaborate and time consuming and involve sophisticated equipment that might not be available in most analytical laboratories. In present paper, interaction of dextromethorphan with some ion-pair reagents was studied by theoretical and calculation methods, and according to the obtained results a dextromethorphan ion-selective potentiomet- ric membrane electrode was developed based on ion- pair compound of dextromethorphan-tetraphenyl- broate (DXM-TPB) as the electroactive substance. The proposed electrode was successfully applied for the de- termination of dextromethorphan hydrobromide in the pharmaceutical formulations and urine samples. Computational chemistry and molecular modeling play an important role in the modern drug discovery [11–15]. Computational work is also valuable in the ОРИГИНАЛЬНЫЕ СТАТЬИ USING DEXTROMETHORPHAN POTENTIOMETRIC MEMBRANE SENSOR IN ANALYSIS OF DEXTROMETHORPHAN HYDROBROMIDE IN PHARMACEUTICAL FORMULATION AND URINE; COMPUTATIONAL STUDY © 2010 M. R. Ganjali 1, 2 , B. Larijani 2 , H. Shams 3 , S. Riahi 1, 4 , F. Faridbod 2 , P. Norouzi 1, 2 1 Center of Excellence in Electrochemistry, Faculty of Chemistry, University of Tehran Tehran, Iran 2 Endocrinology & Metabolism Research Center, Tehran University of Medical Scienc Tehran, Iran 3 Department of Chemistry, Islamic Azad University of Shahreray Branch, Shahreray, Iran 4 Institute of Petroleum Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran Received 20.01.2009; in final form 17.03.2010 Dextromethorphan (DXM) is an antitussive (cough suppressant) drug found in many cough medicines. Dex- tromethorphan has also found other uses in medicine, ranging from pain relief to psychoactive applications. In this study, a potentiometric liquid membrane sensor for simple and fast determination of dextromethor- phan hydrobromide in pharmaceutical formulation and urine was constructed. For the membrane prepara- tion, DXM-tetraphenylborate complexes were employed as electroactive materials in the membrane. The wide linear range (10 –6 –10 –2 M), low detection limit (1 × 10 –6 M), and fast response time (~5 s) characterize the proposed sensors. Validation of the method shows suitability of the sensors for applycations in the deter- mination of dextromethorphan hydrobromide in pharmaceutical formulation and urine. Key words: dextromethophan hydrobromide, potentiometric membrane sensor, urine. УДК 543 N H O Fig. 1. Chemical structure of dextromethorphan hydro- bromide. 5*