Siberian Federal University

A possible mechanism for the concentration and oxidation of tryptophan and 5-hydroxytryptophan on an electrode modified with carbon nanotubes and polyfolic acid has been proposed. The influence of the pH of the solution, the accumulation potential, and the potential sweep speed on the analytical signals of amino acids has been investigated. When the pH increases, the potentials of the anode peaks shift to the region of negative values; the I – pH dependence passes through the maximum with the pH of 6.8. Based on the processing of the dependences of the peak current and the peak potential on the potential sweep speed, it has been found that tryptophan and 5-hydroxytryptophan oxidize with the participation of two electrons and two protons. The transfer process of the first electron limits the electrochemical reaction. The process is controlled by diffusion and adsorption. The diffusion coefficients are equal to 9.7.10–6 cm2/s and 7.4.10–6 cm2/s for tryptophan and 5-hydroxytryptophan, the maximum adsorption value for tryptophan has been 1.63.10–10 mol/cm2 and for 5-hydroxytryptophan it has been 6.41.10–1 mol/cm2. The optimal parameters of concentration and oxidation of tryptophan and 5-hydroxytryptophan in the compresence have been established: the pH of 6.8; the accumulation potential of 0.1 V, the electrolysis time of up to 120 s, the optimal scanning velocity of 120 mV/s. The limit of quantification has been 5.10–8 M