▎ 摘　　要

In this work, thionine (Th) was assembled on the surface of graphene oxide as an electron transfer mediator using diazonium reaction (Th-GO). Then, Th-GO was characterized by different methods such as scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. Afterward, Th-GO was used for the modification of carbon paste electrode. Several electrochemical methods including cyclic voltammetry, differential pulse voltammetry, and hydrodynamic amperometry were used to investigate the behavior of the modified electrode. Then, the role of the modified electrode for oxidation of nitrite has been studied. For this purpose, the effect of critical experimental parameters including step potential and pulse amplitude (in differential pulse voltammetry technique), applied potential, the rotating speed of the disk (in amperometry technique), and the solution pH was investigated. Under the optimized conditions, the currents were found to be linear with the nitrite concentration in the range 0.05-33.0 and 0.5-800 A mu mol L-1 with detection limits of 0.02 and 0.2 A mu mol L-1 using differential pulse voltammetry and hydrodynamic amperometry, respectively. The introduced modified electrode showed good repeatability (RSD% = 3.2) and reproducibility (RSD% = 4.7). This electrochemical sensor was exerted successfully for the determination of nitrite and nitrate in real samples including water and wastewater samples.