Uric acid (UA), a biologically important chemical, exhibits detrimental environmental impacts on farmland as well as groundwater following irrational usage and maintenance. It is well known that determining the con-centration of pollutants is the first step to control environmental pollution. Concerning this fact, a compact thiocyanate (SCN) adlayer based Au electrode was fabricated by a spontaneous immobilization of SCN- ions on a polycrystalline Au surface pertaining to the selective detection of uric acid in a basic medium. The formed adlayer completely shielded the Au surface from routine passivation by uric acid species or its products, pre-venting electrode fouling. To verify the morphology of the electrode surface, cyclic voltammetry (CV), electro-chemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and linear polarization techniques were used. Voltammetric diagnosis revealed that the UA oxidation reaction on the SCN-adlayer based Au electrode basically follows first-order kinetics with a stepped mechanistic approach where one electron transfer is engaged in the rate-determining steps. On top of that, the limit of detection and the sensitivity were estimated to be 0.25 mu M and 0.199 mA cm-2 mM-1, respectively. Interference studies also ascertain the fact that the proposed electrode is reasonably selective in the presence of cohabiting ionic species. Therefore, the developed sensor can be used in the analytical detection of UA in real samples.

The surface of polycrystalline gold (Au (poly)) electrode was ex situ modified with self-assembled monolayer (SAM) of thiourea (TU) with a view of applying the electrode for the electrochemical oxidation of uric acid (UA) in alkaline media. UA undergoes an enhanced electrochemical oxidation at the monolayer of TU-modified Au (poly) (TU|Au (poly)) electrode at a remarkably lower potential with a higher current density as compared to the bare Au (poly) electrode. The enhanced activity of the electrode was achieved due to the effective blocking of harmful adsorption of UA that takes place strongly at the bare Au (poly) electrode surface. The TU|Au (poly) electrode was also found to be very effective towards simultaneous oxidations of UA, ascorbic acid (AA) and dopamine (DA) in their mixture with well separation of the peak current of the individual substance. This technique may be advantageously utilized for developing sensor for the purpose of detection of UA.

In situ chemisorbed hydroxyl ion (OH-) onto clean polycrystalline gold (Au (poly)) electrode showed an extraordinary enhanced electrocatalytic activity towards oxidation of hydrogen peroxide anion (HO2-) in alkaline media. The oxidation of HO2- at the fabricated electrode was found to be a diffusion controlled process. The anodic transfer coefficient of the oxidation reaction was estimated as 0.47. Chloride ion (Cl-) replaced the chemisorbed OH- from the surface of the modified Au (poly) (OH-)Au (poly)) electrode leading to diminishing the observed electrocatalytic activity. The optimized concentration of KOH solution for the highest catalytic activity was found to be ca. 0.1 M. A linear calibration curve for various concentrations of HO2-? in the range of 0.5 to 5 mM was obtained having sensitivity equal to 1.028 A cm-2 M-1.Journal of Bangladesh Academy of Sciences, Vol. 41, No. 1, 29-36, 2017