Aptotic solvents reference electrodes

The calomel electrode. Calomel and other mercurous halides disproportionate in a number of organic solvents, and attempts to use the calomel electrode in polar aptotic solvents, have, for the most part, been unsuccessful. For this reason, it is not advisable to replace the aqueous electrolyte of an ordinary calomel reference electrode with an electrolyte dissolved in an aptotic solvent. 

The silver-silver chloride electrode. The silver chloride reference electrode is not generally suitable as an electrode of the second kind because of the large solubility of AgCl in many aptotic solvents from formation of anionic complexes with chloride ion. In many cases the silver chloride solubility will essentially be that of the added chloride. This contributes significantly to the junction potential in cells with liquid junction and makes the electrode unsuitable for precise potentiometric work. 

The silver-silver ion electrode. One of the most satisfactory and widely used electrodes is the silver-silver ion electrode, which appears to be reversible in all aptotic solvents except those that are oxidized by silver ion. The electrode is easily made by putting a silver wire (or silver-plated platinum) in a solution of 0.001-0.01 M AgN03 or AgC104. The polarizability of these electrodes indicates that if they are to be used in voltammetric work, it should be with a three-electrode circuit (see Figure 5.2b) so that the cell current does not pass through the reference electrode. 

Other reference electrodes for use in polar aptotic solvents. Emphasis has been given to the use of the silver-silver ion reference electrode because it is almost universally applicable, and because standardization on the use of one reference electrode system simplifies the comparison of data between different workers. However, a number of other reference electrodes have been used (see Table 5.4), particularly those that have resulted from the vast amount of batteiy research. These include the Li/Li(solv)+ and other alkali metal electrodes that function reversibly in Me2SO, propylene carbonate, and hexa-methylphosphoramide. The thallium-thallous halide electrodes of the second kind also function reversibly in Me2SO and propylene carbonate. The cadmium amalgam-cadmium chloride reference electrode also functions reversibly in dimethylformamide and may be a useful substitute for the silver-silver ion reference electrode, which may be unstable in dimethyformamide.54... 

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