Talanta 93 (2012) 122–128 Contents lists available at SciVerse ScienceDirect Talanta jo u r n al hom epage: www.elsevier.com/locate/talanta Polymer modified glassy carbon electrode for the electrochemical determination of caffeine in coffee Meareg Amare ∗ , Shimelis Admassie Department of Chemistry, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia a r t i c l e i n f o Article history: Received 24 October 2011 Received in revised form 17 December 2011 Accepted 30 January 2012 Available online 3 March 2012 Keywords: Cyclic voltammetry Square wave voltammetry Caffeine Coffee 4-Amino-3-hydroxynaphthalene sulfonic acid a b s t r a c t 4-Amino-3-hydroxynaphthalene sulfonic acid (AHNSA) was electropolymerized on a glassy carbon electrode. The deposited film showed electrocatalytic activity towards the oxidation of caffeine. The polymer-modified electrode showed high sensitivity, selectivity and stability in the determination of caffeine in coffee. The peak current increased linearly with the concentration of caffeine in the range of 6 × 10 -8 to 4 × 10 -5 mol L -1 , with a detection limit of 1.37 × 10 -7 mol L -1 (LoD = 3ı/slope). Analysis of caffeine in coffee was affected neither by sample matrices nor by structurally similar compounds. Recov- eries ranging between 93.75 ± 2.32 and 100.75 ± 3.32 were achieved from coffee extracts indicating the applicability of the developed method for real sample analyses. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Caffeine (1,3,7-trimethylxanthine) is a naturally occurring alka- loid that is widely found in plant products and beverages. It is a natural stimulant contained in coffee, tea, chocolate, soft drinks and can also be purchased in capsules or tablets for the treat- ment of asthma, nasal congestion, headache or to improve athletic endurance and facilitate weight loss [1]. Almost half of the caffeine consumers ingest caffeine from multiple sources [2,3], the caffeine content of which varies with the type of source [4–6]. In human and animal studies, caffeine produces mental and behavioral effects that are similar to those of typical psychomotor stimulant drugs (e.g., amphetamine and cocaine) [7]. Stimulation of the central nervous system, diuresis and gastric acid secre- tion are the most studied physiological effects caused by caffeine [1]. Habitual coffee and tea drinkers also experience increase in blood pressure when consuming caffeine at the doses found in the commonly consumed beverages; tea, coffee, cola soft-drinks and energy drinks as well as in many pharmaceuticals [8]. Since the caffeine content in coffee is the highest of the common sources [5], a sensitive, fast, selective and inexpensive analytical method for determining caffeine in coffee is highly needed. ∗ Corresponding author. Tel.: +251 918 769541. E-mail address: maerega@yahoo.com (M. Amare). Many methods, including high performance liquid chromatography [9,10], capillary chromatography [11], cap- illary electrophoresis [12], spectroscopy [13,14] and liquid chromatography–tandem mass spectroscopy [15] have been reported for the determination of caffeine in coffee, tea and cola beverages. Usually, these methods demand expensive apparatus, highly skilled technicians, complicated and time-consuming procedures. Compared to these conventional analytical methods, electroanalytical methods are rapid, convenient, of low-cost and environmental-friendly [16]. Polymer-modified electrodes (PMEs) have received consid- erable attention in recent years due to their good stability, reproducibility, increased active sites, homogeneity in electro- chemical deposition and strong adherence to the electrode surface [17–19]. However, among the electroanalytical methods recently reported for the determination of caffeine [20–29], a single work was published based on electropolymerized polymer-modified electrode which could be because of the high interfering back ground current at its oxidative potential [20]. Hence, we planned to develop a polymer-modified electrode that lowers the oxidation potential of caffeine for its determina- tion without a significant influence from background current. To the best of our knowledge, the use of poly(AHNSA) modified GCE for the electroanalytical detection of caffeine is not reported. Hence, we report the preparation of a sensor obtained by electropoly- merizing 4-amino-3-hydroxynaphthalene-sulfonic acid (AHNSA) (Scheme 1(b)) at glassy carbon electrode and its application for the determination of caffeine in coffee. 0039-9140/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2012.01.058