An All-Solid-State Ammonium Ion-Selective Electrode Based on Polyaniline as Transducer and Poly (o-phenylenediamine) as Sensitive Membrane

An all-solid-state ammonium ion-selective electrode, with silver/nano-silver wire as the substrate, polyaniline as transducer and poly (o-phenylenediamine) as sensitive membrane, is presented. The nano-silver was prepared by electrodeposition in 0.1 M AgNO3 standard solution with the half-sine wave at amplitude of 500 mV, frequency of 50 HZ and action time of 1 min. The polyaniline and poly (o-phenylenediamine) were electropolymerized on the surface of the silver/nano-silver substrate by cyclic voltammetry with the scanning potential from 0 to 0.45 V in solutions of 1.0 M aniline hydrochloride and 0.08 M o-phenylenediamine hydrochloride, respectively. Under the SEM, poly (o-phenylenediamine) with 0.5-5 μm in size was evenly and firmly embedded on the surface of the PANI. This ammonium electrode exhibited low impedance of approximately 70 Ohm. It can detect as low as 1.2×10-5 M of ammonium ion, with the slopes of 54.99-55.70 mV per decade (R2>0.99) within a linear range between 2×10-5 M to 0.1 M. It responds as quickly as 0.5-2 s, as well as its lifespan extends to at least 147 days. The electrode showed a superior selectivity toward NH4+, and was successfully applied to detect the NH4+ concentration in real samples. In addition, this electrode is miniature and convenient for package and assembly, which will enable in-situ measurement and long-term monitoring of NH4+ concentration in rivers, lakes and industrial sewage.