Polyaniline pH electrodes

Polyaniline-coated Pt, Pd, and graphite electrodes have been studied. Their potential relationship to pH follows the same principle as the pH glass electrode. They are solid stare involving no redox reactions. The potential is derived from the surface charge density caused by protonation or deprotonation. They act as capacitors. The nonprotonated form of polyaniline was used for pH 6.8 to 1.2 and the protonated form of polyaniline was used for pH 6.8 to 13.0. Three regions of curves (acid, neutral, and alkaline) were obtained. The polyaniline-coated graphite electrode is recommended. It offers the advantage of sturdiness and may be used in microscale in HF solution, at high pressure. At pH 2.2, approximately 4,200 H+ ions were adsorbed by polyaniline per nm(2). An insignificant number of H+ ions were adsorbed by polyaniline at pH 6.2; this is close to its isoelectric point. (C) 1999 Academic Press.