Basic Techniques of Potentiometry in Non-Aqueous Solutions

In potentiometry, we measure the emf of a cell consisting of an indicator electrode and a reference electrode. For emf measurements, we generally use a pH/ mV meter of high input impedance. The potential of the reference electrode must be stable and reproducible. If there is a liquid junction between the indicator electrode and the reference electrode, we should take the liquid junction potential into account. 

In aqueous solutions, the method of measuring electrode potentials has been well established. The standard hydrogen electrode (SHE) is the primary reference electrode and its potential is defined as zero at all temperatures. Practical measurements employ reference electrodes that are easy to use, the most popular ones being a silver-silver chloride electrode and a saturated calomel electrode (Table 5.4). The magnitude of the liquid junction potential (LJP) between two aqueous electrolyte solutions can be estimated by the Henderson equation. However, it is usual to keep the LJP small either by adding the same indifferent electrolyte in the two solutions or by inserting an appropriate salt bridge between the two solutions. 

In contrast, in non-aqueous solutions, the method of measuring electrode potentials has not been well established. The most serious problem is the reference electrode there is no primary reference electrode like the SHE in aqueous solutions and no reference electrode as reliable as the aqueous Ag/AgCl electrode. Thus, various reference electrodes have been employed in practical measurements, making the comparison of potential data difficult. As will be described later, various efforts are being made to improve this situation. 

Redox potential pH Ionic activities Inert redox electrodes (Pt, Au, glassy carbon, etc.) pH-glass electrode pH-ISFET iridium oxide pH-sensor Electrodes of the first land and M /M(Hg) electrodes) univalent cation-sensitive glass electrode (alkali metal ions, NHJ) solid membrane ion-selective electrodes (F, halide ions, heavy metal ions) polymer membrane electrodes (F, CN , alkali metal ions, alkaline earth metal ions) 

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Just as in aqueous solutions, potentiometry is the most fundamental and powerful method of measuring pH, ionic activities and redox potentials in non-aqueous solutions. Here we deal with the basic techniques of potentiometry in non-aque-ous solutions and then discuss how potentiometry is applicable to studies of chemistry in noil-aqueous solutions. Some topics in this field have been reviewed in Ref. [1],... 

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