β Scribed by Orlando Bravo; Reynold T. Iwamoto
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Electrochemical studies in nonaqueous solvents require suitable reference electrodes. The saturated aqueous calomel electrode has been widely used and recommended as a reference electrode in nonaqueous studies, but its use, although convenient, introduces a large liquid-junction potential into the measurement and the possibility of contamination of the test solution with water. A number of investigators have, therefore, examined reference electrodes in individual nonaqueous solvents. These electrodes have been reviewed by Ives and Janz 1.
Acetonitrile is a very popular solvent for electrochemical studies. A reference half-cell of silver-0.10 M silver nitrate solution in acetonitrile has been proposed by Pleskov 2. The potential of this electrode is reproducible in potentiometric measurements, but because of high polarization when current is passed through the half-cell, the reference electrode is not satisfactory for use in conventional polarographic measurements. Although Janz and Taniguchi have pointed out that the tendency of silver chloride to form soluble complexes in acetonitrile makes the silver-silver chloride electrode unsuitable as a reference electrode in acetonitrile 3, Popov and Geske 4 found it possible to achieve an equilibrium condition such that the potential of a silver-silver chloride electrode was reproducible and constant, and the electrode was suitable as a non-polarizable polarographic reference electrode.
The mercury-mercury(I) halide half-cell system in acetonitrile has been studied by Ulich and Spiegel 5 and Cruse et al. 6. The irreproducible and unstable potentials of the chloride, bromide, and iodide half-cell systems have been attributed to disproportionation of the mercury(I) halides in the presence of excess halide ion, into mercury and halomercurate(II) complex species.
In our study, we have found that the mercury-mercury(l) chloride half-cell system is entirely satisfactory as a reference electrode if the chloride concentration is kept very low. To achieve this condition, two sparingly soluble salts were used: potassium chloride and potassium perchlorate. The electrode potential is dependent on the perchlorate concentration, according to the reaction: Hg + KCI + C104 = Β½ Hg2C12 + KCI04 + e (1) A 0.10 F tetraethylammonium perchlorate solution was used to provide a high concentration of perchlorate ion. The characteristics of this electrode, henceforth to be referred to as the acetonitrile calomel electrode (ACE), are discussed in this paper.
π SIMILAR VOLUMES
The preparation in situ of a silver-silver chloride reference electrode includes anodic-cathodic pretreatment of a silver electrode in a phosphate buffer solution comprising 0.1 M sodium chloride. At pH 7.0 and 25Β°C and with optimally pretreated electrodes, the potential of the Ag/AgCl electrode was