Nitrite (NO₂^-) is an important environmental molecule which is found in the natural environment and food because of its application as food preservative [1]. Thus it has gained research interest in both biological and environmental studies because of its health implications [1]. The nitrite ion combines with blood pigments to produce meta-haemoglobin which causes oxygen depletion to the tissues [2]. It also forms highly carcinogenic N-nitrosamine compounds when combined with amines and amides in the stomach [2]. Therefore, quantitative determination of nitrite in drinking water to access its quality, wastewater treatment, in food and for the control of remediation procedures cannot be overemphasized. Several methods have been developed for nitrite determination including electrochemical methods but with one drawback or the other [3]. Many of these procedures are time-consuming, but the electrochemical technique has been identified to provide cheaper, faster and realtime analysis.

In this study, electrocatalytic behaviour of graphene oxide (GO), iron (III) oxide (Fe₂O₃) and Prussian blue (PB) nanoparticles and their nanocomposite towards nitrite (NO₂^-) and nitric oxide (NO) oxidation in neutral and acidic media respectively was carried out on platinum (Pt) modified electrode. Successful synthesis of these nano materials was confirmed using microscopic and spectroscopic techniques. Successful modification of electrode was confirmed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Results showed that the Pt-GO-Fe₂O₃ and Pt-GO-PB nanocomposite modified electrodes gave faster electron transfer process in both 5 mM Ferri/Ferro ([Fe(CN)₆]^3−/4−) redox probe and 0.1 M phosphate buffer solution (PBS). Pt-GO-Fe₂O₃ and Pt-GO-PB electrodes also gave enhanced NO₂^- and NO oxidation current compared with bare Pt and other electrodes studied. Electrocatalytic oxidation of the analyte occurred through a simple diffusion process but characterised with some level of adsorption. Tafel slope b of 468.4, 305.2 mVdec^-1 (NO₂^-, NO); and 311.5, 277.2 mVdec^-1 (NO₂^-, NO) were obtained for the analyte at Pt-GO-Fe₂O₃ and Pt-GO-PB electrode respectively. The limit of detection of these electrodes (LoD) is in the micro molar range and compared favourably with literature reported values. Pt-GO-Fe₂O₃ gave best performance to NO₂^- and NO electrooxidation. The adsorption equilibrium constant β and the standard free energy change ΔG⁰ due to adsorption for the electrodes are discussed. The fabricated sensors are easy to prepare, cost effective and can be applied for real sample analysis of nitrite and nitric oxide in different matrices.

References

1. A. S. Adekunle, J. Pillay and K. I. Ozoemena, Electrochim. Acta, 2010, 55, 4319.

2. J. Davis and R. G. Compton, Anal. Chim. Acta, 2000, 404, 241.

3. X. Wang, E. Adams and A. Van Schepdael, Talanta, 2012, 97, 142.