pH is a unit necessary to know the degree of acidity and alkalinity of a solution. It represents the hydrogen ion activity in the solution. Because the hydrogen ion activity in the solution cannot be directly measured, the pH is measured by comparing with the pH of one aqueous solution. Therefore, clear pH definitions and standards are important, so the ISO (International Organization for Standardization) and the JIS (Japanese Industrial Standards) specify the measurement method for pH 1).
JCSS (Japan Calibration Service System) is a traceability system based on the Measurement Law of Japan. It is developed from time to time and used as a reference material for various official methods in Japan. JCSS are reference materials that ensure traceability to specific reference materials, managed by CERI (Chemicals Evaluation and Research Institute, Japan), a designated calibration institute under the Measurement Law of Japan. JCSS standard solutions are accompanied by a calibration certificate bearing the IAJapan and MRA (Mutual Recognition Agreement) symbols, and the concentrations on the calibration certificate are accepted internationally through the MRA of ILAC/APAC.