A new, highly sensitive Adsorptive Stripping Voltammetric method for levodopa determination was developed. As a working electrode, the glassy carbon electrode (GCE) modified with carbon black (CB), RuO2·xH2O (RuO2) and Nafion was used (CB-RuO2-Nafion GCE). Levodopa signal obtained on the modified electrode was 12 times higher compared to GCE. During research, instrumental parameters were optimized: sampling time ts = 10 ms, waiting time tw = 10 ms, step potential Es = 5 mV and pulse amplitude ΔE = 50 mV. Preconcentration potential Eprec was equal to 0 mV. The best results were obtained in 0.025 M perchloric acid (approx. pH 1.4). Signal repeatability measured on the CB-RuO2-Nafion modified electrode for 0.2 µM of levodopa was equal to 2.1% (levodopa concentration 1 µM, n = 5). Linearity of the method was achieved in the concentration range from 1 to 8 µM. Limit of detection was equal to 17 nM. Recoveries calculated for pharmaceutical products and tap water measurements were in the range 102-105%, which confirms the accuracy of the developed. The applicability of the method was confirmed by analysis of pharmaceutical products and tap water samples. Based on obtained results, it might be concluded that the developed voltammetric method could be a useful tool in routine drug analysis.
Keywords: Nafion; carbon black; levodopa; ruthenium dioxide nanoparticles; voltammetry.