Highly sensitive determination of uric acid in the presence of major interferents using a conducting polymer film modified electrode S. Brillians Revin, S. Abraham John ⁎ Centre for Nanoscience & Nanotechnology, Department of Chemistry, Gandhigram Rural Institute, Gandhigram — 624 302, Dindigul, Tamilnadu, India abstract article info Article history: Received 7 February 2012 Received in revised form 17 May 2012 Accepted 21 May 2012 Available online 30 May 2012 Keywords: 3-Amino-5-mercapto-1,2,4-triazole Uric acid Ascorbic acid Dopamine Tyrosine Methionine This paper describes the sensitive and selective determination of uric acid (UA) in the presence of important in- terferences, ascorbic acid (AA), dopamine (DA), tyrosine (Tyr) and methionine (Met) at physiological pH using an electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole on glassy carbon (p-AMTa) electrode. The p- AMTa electrode shows an excellent electrocatalytic activity towards UA. This was understood from the observed higher oxidation current and heterogeneous rate constant (3.24×10 -5 ms -1 ) for UA when compared to bare GC electrode (4.63 ×10 -6 ms -1 ). The selective determination of UA in the presence of 1000-fold excess of AA was achieved using p-AMTa electrode. Further, the p-AMTa electrode was successfully used for the simultaneous and selective determination of UA in the presence of important interferences, DA, Tyr and Met. Using ampero- metric method, 40 nM UA was detected for the first time. The current response of UA was increased linearly while increasing its concentration from 40 nM to 0.1 mM and a detection limit was found to be 0.52 nM (S/ N=3). Finally, the practical application of the present method was demonstrated by determining UA in human urine and blood serum samples. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Uric acid (UA, 2,6,8-trihydroxypurine) is the main end product of pu- rine nucleotide catabolism in human body. It is well known that UA was present in human blood serum, plasma, urine and saliva [1]. Serum UA was a risk factor for the oxidative stress [2], coronary heart disease [3] and closely linked to vascular nitric oxide activity [4]. Elevated serum UA was associated with a risk of cardio-vascular disease [5], peripheral arterial disease [6], chronic kidney disease [7], non-alcoholic fatty liver disease [8] and silent brain infarction [9]. Increased consumption of serum UA can act as a scavenger of radicals and thus preventing from Parkinson's disease (PD) [10]. However, low UA levels in plasma and urine associate with worse cognitive performance in PD [11]. UA is a pathogenic factor in pre-eclampsia for pregnant women [12,13]. It acts as a role of insulin resistance in older [14] and pregnant women [15]. Re- duced level of plasma UA leads to Schizophrenia [16] and blood UA levels contributed with sleep-disordered breathing [17]. Low concentration of UA associated with multiple sclerosis [18] and also altered UA level are associated with sex and age interaction [19]. Urinary UA is related with risk of Down syndrome for children and adults [20]. Normally, UA levels in serum range from 240 to 520 μM and in urinary excretion it ranges from 1.4 to 4.4 mM [21]. Ascorbic acid (AA) coexists with UA [21,22] and hence it is a main interference for UA determination in human fluids. Therefore, an accurate determination of UA is essential in the presence of AA in human fluids to secure the human health. Since both of them oxidized at the same potential in physiological pH, it is a challenging task for the analytical chemists to determine UA in the presence of large excess of AA. Thus, the aim of the present study is to de- termine UA in the presence of much higher concentration of AA. Few pa- pers were published in the literature for the determination of AA/UA ratio of more than 1000 [23–26]. However, the electrodes used in these papers have several drawbacks including tedious procedure involved in the modification of the electrode, reproducibility of the electrode modifica- tion was uncertain and a more time consuming process. For example, Hasan and co-workers have followed a very tedious procedure for the modification of the electrode; (i) mechanically grinded the GC or graphite electrode with struers silicon carbide (SiC) paper of 240-, 500-, 1200-, 2400- and 4000-grit and (ii) grinded by SiC with successively decreasing diameter and (iii) finally fine polished with 1-μm diamond paste [23–26]. Kang and Lin have prepared the RNA modified GC electrode for the deter- mination of UA in the presence of AA and DA by applying a stationary de- position potential in a solution containing RNA for 30 min followed by cycling in a potential window from -0.2 V to +0.8 V for 4 cycles [24]. On the other hand, Li and Lin have used a tedious procedure for the fab- rication of gold nanocluster modified overoxidized pyrrole electrode for the determination of UA in the presence of a 1000-fold higher concentra- tion of AA. For the fabrication of the modified electrode, they first cycled the bare GC electrode in the potential window from -0.35 V to +0.85 V in a solution containing pyrrole and sodium dodecyl sulfate and then transferred the electrode into NaOH solution followed by overoxidation at a constant potential of +1.0 V for several minutes and finally electro- chemically deposit the gold nanoclusters on the modified electrode by Bioelectrochemistry 88 (2012) 22–29 ⁎ Corresponding author. Tel.: + 91 451 245 2371; fax: + 91 451 245 3031. E-mail address: abrajohn@yahoo.co.in (S.A. John). 1567-5394/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.bioelechem.2012.05.005 Contents lists available at SciVerse ScienceDirect Bioelectrochemistry journal homepage: www.elsevier.com/locate/bioelechem