Please cite this article in press as: M.A. Raj, S.A. John, Simultaneous determination of uric acid, xanthine, hypoxanthine and caffeine in human blood serum and urine samples using electrochemically reduced graphene oxide modified electrode, Anal. Chim. Acta (2013), http://dx.doi.org/10.1016/j.aca.2013.02.017 ARTICLE IN PRESS G Model ACA-232403; No. of Pages 7 Analytica Chimica Acta xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Analytica Chimica Acta j ourna l ho me page: www.elsevier.com/locate/aca Simultaneous determination of uric acid, xanthine, hypoxanthine and caffeine in human blood serum and urine samples using electrochemically reduced graphene oxide modified electrode M. Amal Raj, S. Abraham John ∗ Centre for Nanoscience and Nanotechnology, Department of Chemistry, Gandhigram Rural Institute, Gandhigram 624 302, Dindigul, Tamilnadu, India h i g h l i g h t s ◮ Glassy carbon electrode was modi- fied with graphene by self assembly method. ◮ Modified electrode was character- ized by Raman spectroscopy. ◮ Graphene modified electrode sep- arated the voltammetric signals of four purine derivatives. ◮ Selective and simultaneous deter- mination of four purine compounds were achieved. ◮ Practical application was demon- strated in human blood serum and urine samples. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 23 November 2012 Received in revised form 3 February 2013 Accepted 8 February 2013 Available online xxx Keywords: Graphene oxide Electrochemical reduction Raman spectra Purine derivatives Human blood plasma a b s t r a c t This paper describes the fabrication of graphene on glassy carbon electrode (GCE) by electrochemical reduction of graphene oxide (GO) attached through 1,6-hexadiamine on GCE and the simultaneous deter- mination of structurally similar four purine derivatives using the resultant electrochemically reduced GO (ERGO) modified electrode. The electrocatalytic activity of ERGO was investigated toward the oxidation of four important purine derivatives, uric acid (UA), xanthine (XN), hypoxanthine (HXN) and caffeine (CAF) at physiological pH. The modified electrode not only enhanced the oxidation currents of the four purine derivatives but also shifted their oxidation potentials toward less positive potentials in contrast to bare GCE. Further, it successfully separates the voltammetric signals of the four purine derivatives in a mixture and hence used for the simultaneous determination of them. Selective determination of one purine derivative in the presence of low concentrations other three purine derivatives was also realized at the present modified electrode. Using differential pulse voltammetry, detection limits of 8.8 × 10 -8 M, 1.1 × 10 -7 M, 3.2 × 10 -7 M and 4.3 × 10 -7 M were obtained for UA, XN, HXN and CAF, respectively. The practical application of the modified electrode was demonstrated by simultaneously determining the concentrations of UA, XN, HXN and CAF in human blood plasma and urine samples. © 2013 Elsevier B.V. All rights reserved. ∗ Corresponding author. Tel.: +91 451 245 2371; fax: +91 451 245 3031. E-mail addresses: abrajohn@yahoo.co.in, abrajohn@gmail.com (S.A. John). 1. Introduction Purine bases and their derivatives play an important role in the functioning of living systems [1]. Purines are involved in many metabolic processes as cofactors which play key roles in biologi- cal fundamental processes [2]. Several pathological conditions alter the levels of purine derivatives in blood serum and urine which are 0003-2670/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aca.2013.02.017