A highly sensitive electrochemical sensing probe incorporating classical Berthelot's reaction and glassy carbon electrode for measuring ultra-trace levels of ammonia/ NH4+ in water

Abstract

In quantifying NH₃ and/or NH₄⁺ ions, the wavelength-based spectrochemical methods involving formation of colored products of the Berthelot’s or Nessler reactions might be challenging due to auto-self absorbance, spectral overlap, and background scattering noise. Thus, the current study reports a renewable glassy carbon electrode (GCE) sensing probe combined with Berthelot’s reaction (indophenol formation) and adsorptive square - wave-anodic stripping voltammetry (Ads SWSV) at pH = 10 for detection of NH₃ and/or NH₄⁺ in water. The redox characteristics and the high surface coverage of the oxidation product of indophenol on the sensing platform suggested its use for NH₃ and/or NH₄⁺ detection. The electrochemical sensing probe for NH₄⁺ displayed good linear relationship between 5.56 nM and 55.6 μM of NH₄⁺ with limits of detection (LOD) and quantitation (LOQ) of 4.83 × 10^-9 and 1.47 × 10^-8 M, and sensing probe sensitivity of 1.27μA/μM⁻¹ cm⁻², respectively. The probe was applied for measuring NH₃/NH₄⁺ in fresh and seawater samples, and the results were validated using standard ion chromatography (IC) and micro spectrophotometry assays. The assembled probe was also tolerably selective against interfering of other contaminants in a comparable potential window. Additionally, the probe has exceptional selectivity, long-term stability, and repeatability, and has good capacity to detect NH₃ and/or NH₄⁺ ions with high accuracy (recovery range = 97.14 ± 4.12–102.9 ± 4.7) in environmental water samples. The calculated Student t_exp and F_exp values (n = 5) were less than the tabulated t_tab (2.78) and F_tab (6.39) at 95 % probability (P = 0.05, n = 5). The study offer high reliability towards NH₃ and/or NH₄⁺ detection in complex environments.