Aqueous electrolyte solution, which may be gelled, containing fixed concentration
of hydrogen ions, e.g.
HCl
or a buffer solution, and a fixed concentration of the ion to which the
internal reference electrode is reversible, e.g. chloride ion in the case of silver-silver chloride, or calomel
electrodes.
Source:
PAC, 1985, 57, 531
(Definition of pH scales, standard reference values, measurement of pH and related
terminology (Recommendations 1984))
on page 540