Electrochemical sensing of hydroxylamine using a wax impregnated graphite electrode modified with a nanocomposite consisting of ferric oxide and copper hexacyanoferrate

The authors describe a wax-impregnated graphite electrode modified with ferric oxide (Fe₂O₃) and copper hexacyanoferrate(II), and its application as an electrochemical sensor for hydroxylamine. The presence of Fe₂O₃ nanoparticles enhance the electron transfer kinetics and electrocatalytic activities, and also enlarge the surface area of the modified electrode. As compared to the unmodified electrode, 16.9 and 30.1 fold enhancements in amperometric response was observed for copper hexacyanoferrate(II) and the nanocomposite modified electrodes, respectively. Also, the presence of Fe₂O₃ in the nanocomposite enhances the anodic current response by 1.78 fold when compared to copper hexacyanoferrate(II) alone modified electrode. The electron transfer coefficient, electron transfer rate constant, diffusion coefficient and catalytic rate constant for the electro-oxidation of hydroxylamine were determined. Amperometry performed at a working voltage of 750 mV (vs. Ag/AgCl) revealed a detection range that extends from 0.8 μM to 100 μM, a detection limit of 0.5 μM (at an S/N ratio of 3) and a sensitivity of 0.0924 mA⋅mM⁻¹. The modified electrode is remarkably stable and was successfully applied to the determination of hydroxylamine in spiked water samples. (author)