Stability of the Inner Polyaniline Solid Contact Layer in All-Solid-State K⁺-Selective Electrodes Based on Plasticized Poly(vinyl chloride)

Abstract

A simple and powerful method based on UV-visible spectroscopy is presented for studying the stability of the inner electrically conducting polyaniline (PANI) solid contact (SC) layer in all-solid-state ion-selective electrodes (ISE). The influence of the plasticized poly(vinyl chloride) (PVC) membrane (ISM) composition and the pH of the sample solution on the stability of the solid contact is reported. PANI is used as a model compound in this study, but the method presented is universal and can be applied to different types and combinations of SCs and ISMs. It provides a tool for finding the best combination of conducting polymer and ISM for solid contact ISEs. PANI is deposited electrochemically either on glassy carbon or quartz glass covered with a thin layer of tin oxide, and a K+-selective ISM is deposited on top of the PANI layer. The short-term stability of the inner PANI layer is good for all membrane types in buffer solutions with pH 2, 6, and 9, indicating that the outer plasticized PVC membrane hinders the emeraldine salt-emeraldine base transition of the highly pH sensitive PANI layer. The solid contact K+-selective electrodes studied showed a Nernstian response of 58.2 +/- 0.1 mV/log aK. Significant differences are observed in the long-term stability of the inner PANI layer between the different membrane types. This indicates that water uptake of the PVC membrane and its permeability to OH- ions are critical parameters affecting the stability of the PANI layer. The solid contact electrodes based on PANI may require a composition of the PVC membrane different from those typically used in conventional ISEs with an inner solution.

Nitrate‐Selective Solid Contact Electrodes with Poly(3‐octylthiophene) and Poly(aniline) as Ion‐to‐Electron Transducers Buffered with Electron‐Ion‐Exchanging Resin

“…Therefore, in combination with a soluble conducting polymer, the resin seems a promising agent for buffering both redox and acidic state in the transducing layer. This can be especially advantageous for poly(aniline) because PANI is sensitive to acid-base influences [12,15,27,28]. The reported values for redox and pH buffer capacity of the resin are 10 -12 and 1.5 -2 mg-equivalent/g [23 -25].…”

An All-solid-state Cd2+-selective electrode with a low detection limit

“…However, the potential instability and irreproducibility of such coated-wire electrodes (CWEs) may arise as consequence of poor ion-to-electron transduction between the ionically conducting ion-selective membrane and the electronic conductor, and water layer formed at the interface. These problems have been solved by introducing a variety of intermediate solid contacts, such as conducting polymers [11][12][13][14], redox-active selfassembled monolayers (SAMs) [15,16], or carbon nanotubes [17]. Through continuous efforts, state-of-the-art ASS-ISEs have reached performances comparable or superior to those of electrodes with internal filling solutions.…”

Solid‐Contact Potentiometric Sensor Based on Polyaniline and Unsubstituted Pillar[5]Arene

“…Besides oxides and complexes of transient metals, conducting polymers are intensively applied in solid-contact potentiometric devices. PANI, polypyrrole and polythiophene derivatives are described in the assembly of the solid-contact sensors for the detection of alkali and alkali-earth metals [2][3][4][5], transient metals [6][7][8][9], inorganic anions [10,11] and charged organic species [12].…”