Electrochimica Acta 91 (2013) 36–42 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al h om epa ge: www.elsevier.com/locate/electacta Simultaneous determination of dopamine and uric acid in biological samples on the pretreated pencil graphite electrode Esmaeel Alipour a,∗ , Mir Reza Majidi a , Afsaneh Saadatirad a , Sayed mahdi Golabi a , Ali Mohammad Alizadeh b a Electroanlytical Chemistry Lab. Department of Analytical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran b Cancer Research Center, Tehran University of Medical Sciences, Tehran, Iran a r t i c l e i n f o Article history: Received 17 October 2012 Received in revised form 11 December 2012 Accepted 19 December 2012 Available online 27 December 2012 Keywords: Pretreated pencil graphite electrode Uric acid Dopamine Differential pulse voltammetry Human serum Urine a b s t r a c t An electrochemically pretreated pencil graphite electrode (PGE) has been proposed for simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of high levels of ascorbic acid (AA). The electrochemical pretreatment of PGE was achieved in phosphate buffer (pH 7) by the potential recycling between 1.5–2.0 V/SCE for 100 cycles, and at the scan rate of 100 mV s -1 . The influence of electrochemical pretreatment of PGE on the separation of overlapped peaks of AA, DA and UA were studied and optimum conditions were suggested. Differential pulse voltammetry (DPV) was used for simultaneous determina- tion of DA and UA in the presence of high concentrations of AA. The peak separation between DA and AA, and also between DA and UA was up to 260 and 160 mV, respectively. The calibration curves were in the range of 0.15–15 M and 0.3–150 M for DA and UA in the presence of AA, respectively. The detection limits (S/N = 3) were 0.033 and 0.12 M for DA and UA, respectively. The results reveal that pretreat- ment of the pencil graphite electrode surface not only improves its electrochemical catalytic activities towards the oxidation of DA and UA, but also resolves the overlapped oxidation peaks of AA, DA and UA into three well-defined peaks. The present method can apply for UA and DA determination in human serum and urine, and also for some commercial pharmaceutical samples without additional sample pre-treatment. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Dopamine, ascorbic acid, and uric acid are important human body compounds that play determining role in metabolism [1], hence, monitoring the their concentration in biologic fluids such as blood and urine may prevent and control many diseases. These are electrochemically active compounds that can be deter- mined by different techniques. In recent years, the development of voltammetric methods for their determination in human body fluids such as urine and serum has received consider- able interest. However, in most cases, overlapped voltammetric responses, poor selectivity and low reproducibility make their simultaneous tracking highly difficult [2]. To overcome these prob- lems, various modified electrodes have been constructed and used such as organic redox mediators modified electrode [3], polymers modified electrodes [4–10], nanoparticles modified elec- trodes [11–14], boron-doped diamond modified electrode [15], ∗ Corresponding author. Tel.: +98 411 3393126; fax: +98 411 3340191. E-mail address: i-alipour@tabrizu.ac.ir (E. Alipour). carbon–ceramic modified electrode [16], pyrolytic graphite mod- ified electrodes [17,18], screen-printed carbon modified electrode [19], carbon ionic liquid modified electrode [20], carbon nan- otube modified electrodes [13,21–23], RNA modified electrode [24], and finally glassy carbon electrode modified via electrochemi- cal oxidation [25]. In spite of selectivity of these voltammetric techniques, cheaper or more sensitive and selective methods are still needed to develop detection routes for uric acid and dopamine in the presence of AA due to their clinical signifi- cance. Electrochemical pretreatment of pencil graphite electrode seems to be a simple, less time consuming and more applica- ble strategy in comparison to other procedures. This strategy eliminates the use of some toxic compounds required in mod- ification of electrode surface. Recently, we have successfully used electrochemically pretreated pencil graphite electrode for development of various DNA hybridization biosensors [26–31]. In the present study, a simple sensor based on PPGE described for simultaneous determination of DA and UA in the pres- ence of high levels of AA. The analytical performance of this sensor was evaluated by differential pulse voltammetry technique. 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.12.079