The Electrolyte of Reference Electrodes

The electrolyte solution of reference electrodes may serve two functions (a) to provide a constant potential of the reference electrode, and (b) to serve as the electrolyte bridge to the analyte solution, ideally with negligible diffusion potentials. The possibilities to contact the reference electrode to the adjacent solution vary greatly. The most common arrangements are shown in Fig. III.2.6. A detailed description of the diaphragms is given below. When such an arrangement is used, the levels of the analyte and the reference electrode electrolytes should be balanced to prevent any contamination, either of the analyte or the reference electrode compartment. 

Very often it is imperative to prevent any contact between the analyte solution and the reference electrolyte solution, and this can be achieved by an additional 

At a diaphragm two solutions are separated from each other. When these two solutions consist of different electrolytes or electrolytes in different concentrations, a diffusion of the constituent of the solutions occurs. This leads to a potential difference, which is called a liquid-junction potential, the magnitude of which depends strongly on the composition of the solutions. Ideally, this liquid-junction potential should be very small and constant to minimise errors. To estimate liquid-junction potentials, the Henderson equation is applicable [23]  

The most important reference systems (calomel electrode, silver/silver chloride electrode) contain chloride ions. Here, mostly potassium chloride solutions are used, because the mobility of potassium ions (76.2 x 10 cm V s in infinitely diluted aqueous solution at 25 C) and chloride ions (79.1 x 10 cm V s in infinitely diluted aqueous solution at 25°C) are quite similar [1]. Considering two 

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