In the first section of this study, Thionin (Th), as a mediator for electron transfer, was linked on the surface of graphene oxide by diazonium reaction. Then, carbon paste electrode was modified with the nanocomposite and the charcteristics were studied with different electrochemical methods. The cyclic voltammograms showed that the electrochemical ehavior of the modified electrode is diffusion controlled and pH dependent. The modified electrode showed electrocatalytic behavior toward oxidation of Nitrite. The effect of some experimental parameters such as step potential and pulse amplitude (in differential pulse voltametry tequnice), applied potential and rotating speed of disk (in amperometery tequnice) were investigated.for simultaneous determination of nitrite and nitrate was used flow injection analysis method with a copper-coated cadmium reductor column. Nitrate was reduced to nitrite in reductor column containing copperised cadmium. Then,nitrite was determinated with using electrocatalytic effect Thionin-GO nanocomposite on oxidation of nitrite. Under the optimized conditions, currents were found to be linear with the concentration of nitrite by using differential pulse voltametry and amperometery method in the range of 0.05 to 33.0 mmol L -1 and 0.5 to 700.0 µmol L -1 , respectively. The detection limits were found to be as 0.02 mmol L -1 and 0.2 µmol L -1 for differential pulse voltametry and amperometery method, respectively. The proposed modified electrode showed good repeatability and reproducibility. This method was successfully applied for the determination of nitrite in real sample. In the second section of this study, a nitrate electrochemical sensor is introduced based on Ni-Al@rGO-LDH nanohybrid. Then, the nonohybrids structure was characterized by transmittance electron microscopy, X-ray diffraction, fourier transform infrared spectroscopy and cyclic voltammetry. Electrochemical studies showed that Al@rGO-LDH nanohybrids has high electrocatalytic activities on nitrate reduction. In determination of nitrate were used hydrodynamic amperometry method with flow injection analysis. Various analytical parameters such as pH¸ applied potential and flow rate were studied and optimized. under optimized conditions the calibration graph was linear for.0.05-2.5 µmol L -1 . And 2.5-800.0 µmol L -1 . In continue of this work. Five different Al@rGO-LDH /CPEs were tested separately for the amperometric response of nitrate, providing a relative standard deviation (R.S.D.) 3.9%. The selectivity of the modified electrode was studied. The applicability of Al@rGO-LDH /CPEs was investigated by determining nitrate in water samples with satisfactory results.
