pH Standard and Technical Buffer Solutions

A prerequisite for an accurate pH calibration is the availability of a suitable liquid buffer solution.

pH buffer solutions are mixtures of weak acids and the salt of these acids combined with a strong base, or mixtures of weak bases and the salt of these bases combined with a strong acid. Buffer solutions are notable by the fact that they resist change to their pH value regardless of additions of small quantities of acids or bases. Their hydrogen ion activity is stable over a wide range of dilution or concentration.

The National Institute of Standards and Technology (NIST) recommends nine different buffer solutions for the exact calibration of pH measuring systems. These NIST buffer solutions also serve as reference points for the pH scale, as it is impossible to prove the activity of single hydrogen ions by measurement.

All buffer solutions which are produced according to the NIST formulas are called Standard Buffer Solutions. As the activity of the hydrogen ions is temperature dependent, so is the pH value of any buffer solution. The temperature dependency of the NIST standard buffer solutions is given in the table below.