reference value pH standard

An aqueous solution of 0.05 mol potassium hydrogen phthalate per kg water which is the reference value for the definition of pH(RVS) values in the temperature range 0-95 °C.
See also: operational pH standard, primary pH standard
PAC, 1985, 57, 531 (Definition of pH scales, standard reference values, measurement of pH and related terminology (Recommendations 1984)) on page 540