A novel all-solid-state ammonium electrode with polyaniline and copolymer of aniline/2,5-dimethoxyaniline as transducers

• In this study we reported an all-solid-state ammonium ion selective electrode.
• Polyaniline and copolymer of aniline/2,5-dimethoxyaniline were used as transducer.
• The dime-size electrode is easy to be integrated with diameter of 0.6 mm.
• Its response time is <1 second, lifetime is >3 months.
• It was suitable for in-situ monitoring of NH4+ in pH range of 2.6–10.1.

From the centre outwards, the novel all-solid-state ammonium ion-selective electrode was composed of a silver wire as substrate, covered with conductive polyaniline (PANI), copolymer of aniline/2,5-dimethoxyaniline (CPANI) and ion selective membrane (ISM) layers. PANI was formed in-situ on the Ag wire by the cyclic voltammetry method, scanned from 0 to 0.45 V in 0.1 M aniline hydrochloride solution, and then dipped the electrode in the N,N-Dimethyl formamide (DMF) solution of CPANI and ISM sequentially. The scanning electron microscope (SEM) observation revealed that the PANI formed cross-linked slabs about 0.3–2.5 μm in length and 0.3–0.6 μm in thickness. Under the SEM, CPANI micro particles filled in the cross-linked PANI slabs. Bulk impedance of the transducer was between 100 and 200 Ω, much lower than the poly (vinyl chloride) (PVC) based transducer in the previous work. Fabrication procedures, micro-structure, and the common resolvability of the CPANI and ISM in the DMF were all essential for reducing the cross-boundary resistance. Linear response range of the electrode was 10−4–10−1 M, with a Nernst slope of 54.20–56.59 mV/decade. The potential drifts of each decade were ±0.5 mV within 400 s. The response time was less than 1 s and the lifetime was three months. The ammonium electrodes were used to test the ammonium in the waste water with pH value from 2.6 to 10.1, and the testing results were in agreement with those obtained by titration method and Nessler’s reagent colorimetry method. The ammonium electrode proposed in this paper is suitable for in-situ monitoring NH4+ content in the environment in a wide range of pH value.