Application of an ammonium ion-selective electrode for the real-time measurement of ammonia nitrogen based on pH and temperature compensation

Abstract

Traditional methods for determining the ammonia nitrogen (NH3-N) concentration are the colorimetric method using Nessler’s reagent or salicylate. To prevent secondary pollution, minimise the time required for measurement, and reduce cation interference, new NH3-N measurement methods have been developed including fluorescence, gas phase molecular absorption spectrometry, and ammonia gas sensing electrode methods. However, in these techniques, the addition of a chemical reagent is unavoidable, so the real-time and accurate measurements of NH3-N are achieved hardly. In this study, we used an ammonium ion-selective electrode (ISE) for the real-time measurement of NH3-N with compensation for the ammonium ion (NH4+) component of the total NH3-N concentration. The basic mechanism is that an ammonium ISE can measure NH4+ concentration, and NH4+ ratio in NH3-N can be calculated based on pH and temperature. Experimental results indicate that the ammonium ISE exhibited near-Nernstian behaviour, having a fitted line with a slope of 56.4 mV/pNH4. The compensation effects and reproducibility are good. Furthermore, the difference in the temperature responses at different NH4+ concentrations agrees with the Nernst equation basically. Therefore, the proposed method can provide a real-time and environmentally friendly solution to determine NH3-N concentration.