GALLY PROOF 1 10323 INTRODUCTION The discovery of CNTs has had a profound effect on elec- troanalysis. The properties and applications of CNTs them- selves have been studied in cyclic voltammetry. However, the modification of CNTs has recently been the focus of much research, primarily to improve their solubility in various sol- vents. Modified CNT electrodes also allow the electrochemist to tailor the properties of the CNT or the electrode surface, to impart any desired properties such as enhanced sensing capa- bilities. In the electrochemical modifications, strategies and research were carried out using modified CNT for electroana- lytical and bioanalytical applications 1- 4 . In analytical applications based on the effects produced upon modification of different solid electrodes, especially glassy carbon electrode (GCE) substrates with CNT, the modi- fications were most usually carried out by coating or prepar- ing CNT-binder composite electrodes. Simple modified elec- trode designs can be obtained by incorporation of a small amount of CNT dispersion onto a GCE 5-8 . Carbon nanotubes- modified GCE are primarily used for the detection of non- metallic compounds, especially biochemical compounds 9 . Carbon nanotubes-modified electrodes like GCE may be considered as a viable alternative to mercury-based procedures Electrochemical Reduction of Manganese Mediated by Carbon Nanotubes/Li + Modified Glassy Carbon Electrodes W. TAN, M. RADHI * , M. AB RAHMAN and A. KASSIM Department of Chemistry, Faculty of Science, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia *Corresponding author: Tel: +60 132916400; Fax: +60 3 89432508; E-mail: mmrchm2007@yahoo.com; mmradhi@yahoo.com Asian Journal of Chemistry; Vol. 23, No. 6 (2011), 0000-0000 Received: ; Accepted: ) AJC 0000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Glassy carbon electrodes (GCE) were modified with carbon nanotubes (CNT) with and without Li + dopant by a mechanical attachment method. These modified working electrodes, abbreviated as CNT/Li + /GCE and CNT/GCE, produced two reduction peaks of Mn(II) at +0.8 and +0.1 V vs Ag/AgCl in 0.1 M KHPO4, which appeared irreversible during cyclic voltammetry. The sensing characteristics of the modified film electrodes demonstrated in this study were composed of: (i) a wide working potential window ranging from +1.8 to -1.8 V (depending on different scan rates, pH, concentration and temperature); (ii) a wide applicable pH range (from at least 2-10); (iii) a wide applicable temperature range from 5-90 ºC; (iv) a current response that is stable and fast with a satisfactory and reproducible linear voltammetric and amperometric response to various analytes; (v) a good reproducibility and recovery rate in seawater and blood; (vi) interfering metal ions such as Hg 2+ , Cd 2+ and Cu 2+ appeared to pose positive interference on the reduction peaks of Mn 2+ . The reduction current of Mn 2+ using CNT/Li + /GCE was largely influenced by concentration, pH, temperature and scan rate. Based on the calibration curve obtained, a linear graph of up to 1 mM Mn(II), with an impressive sensitivity response of 66.7 μA/mM, was obtained. Based on chronoamperometry, a diffusion coefficient for Mn 2+ of 1.53 × 10 -7 cm 2 /s was determined. Key Words: CNT/Li + /GCE, Mn(II), Electrocatalyst, Cyclic voltammetry. in studying some heavy metals Cd(II) and Pb(II) by cyclic voltammetry 10,11 . The mechanism of the electrochemical reaction with lithium of the modified CNTs was studied by X-ray diffrac- tion lithium was first intercalated in the activated multi-walled nanotubes between graphene layers, forming n-stages. Interlayer expansion and misfits between curved layers caused fracturing and exfoliation of the CNT with an irreversible loss of staging phenomena. The resulting solids displayed improved capacity retention on successive cycles. These results support a new strategy to improve the electrochemical performance of graphitized CNT 12-14 . Analysis of Mn(II) is usually carried out using spectro- scopic methods such as ICP.AAS and less commonly done using voltammetric methods. Our experience shows us that the voltammetric detection of Mn(II) is not easily carried out on the electrode surface of glassy carbon electrodes. How- ever, a modified GC electrode with a lecithin film was reported to improve the redox reaction of ascorbic acid in the presence of the Mn(II) ion 15 . Manganese is an interesting element for voltammetric studies as it has many oxidation states, from zero and +1 up to +7. Manganese compounds, where manganese is in an oxida- 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62