Abstract
Electrochemical oxidation of amino acids is a complex process influenced by factors such as amino acid structure, electrode material, pH value, and medium composition. The kinetics of such reactions can be studied using voltammetry with linear and cyclic potential scans. Voltammetric studies were conducted on the electrochemical oxidation of tryptophan using nickel-based nanostructured electrode arrays modified with platinum. The analysis of the voltammograms showed that the depolarizer discharge intensity was 1.45 times higher on the modified electrode compared to the smooth platinum electrode. The absence of cathodic current maxima, clearly visible on the anodic sections of voltammograms, indicates the irreversibility of the oxidation process, meaning the reaction product is electrochemically inactive within the reverse potential scan range. The irreversible reaction involves two electrons, and the oxidation products of tryptophan tend to adsorb onto the electrode surface, affecting the rate of the electrochemical process. Calculations established a linear dependence of peak current on tryptophan concentration within the range of 1×10⁻⁴–1×10⁻² mol/dm³, with the calibration curve equation given as: Imax = (0.62 ± 0.01) + (61.17 ± 2.62) × C(tryptophan) mol/dm³ (R² = 0.991; n = 6). The detection limit of tryptophan, determined using the 3s criterion, was 4.9×10⁻⁴ mol/ dm³, enabling its quantification within the range of 5×10⁻⁴–1×10⁻² mol/dm³. The rate constant, activation energy, and diffusion coefficient of the oxidation process were calculated based on voltametric data and corresponding kinetic equations. Temperature increase enhanced the discharge intensity and induced polarization by 60 mV. The findings help evaluate the redox properties of tryptophan on electrodes further modified by platinum deposition. Additionally, variations in electrode surface structure significantly influenced reaction kinetics, highlighting the potential of nanostructured platinum electrodes for improved electrocatalysis. The study provides a fundamental understanding of electrochemical oxidation mechanisms that can be applied to biochemical sensing and analytical chemistry.