filling solution

of a reference electrode
https://doi.org/10.1351/goldbook.F02365
Solution containing the @[email protected] to which the @[email protected] of the @[email protected] is reversible, e.g. chloride for silver-silver chloride electrode. In the absence of a @[email protected], a high concentration of filling solution comprising cations and anions of almost equal @[email protected] is employed as a means of maintaining the @[email protected] potential small and approximately constant on substitution of @[email protected] for @[email protected]
Source:
PAC, 1985, 57, 531. (Definition of pH scales, standard reference values, measurement of pH and related terminology (Recommendations 1984)) on page 541 [Terms] [Paper]