The concept of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909. Through studying the effect of ion concentration on proteins he found that the hydrogen ion concentration was particularly important and introduced the pH scale as a simple way of expressing it.
The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in a solution. That is, the degree of acidity or alkalinity of a solution is based on the inverse of the hydrogen ion concentration.
The scale of pH runs from 1 to 14. Solutions with a pH of 7 are considered neutral with those less than 7 are acidic whilst those above 7 are alkaline.
The pH value is temperature dependent due to the molecular equilibrium of a solution undergoing changes in state due to temperature changes thereby affecting the nature of the solution. The pH change is inversely proportional to the temperature, that is, an increase in temperature sees a decrease in pH and vice versa.
The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or a colour-changing chemical indicator. The glass electrode is the most widely used pH-indicator electrode being applicable over a wide pH range and exhibiting high stability, reliability and reproducibility.
To verify the proper functioning of a glass electrode and the accuracy of the instrument over the pH range of the test solution, the pH meter assembly is calibrated at least at two calibration points with calibrants (pH buffer solutions of certified value) which bracket the pH of the sample. Furthermore, since pH values are temperature dependent the pH electrode is calibrated with buffers that have certified pH values at different temperatures. Since pH meters are unable to correct sample pH values to a reference temperature, due to the unique pH versus temperature relationship of each sample, the calibration and measurements are performed at the same temperature.
ROMIL-PrimAg® -TpH SI-traceable pH reference solutions are accredited to ISO 17034 and come supplied with a Certificate of Calibration reporting the certified pH value at 20°C with associated uncertainty.
PrimAg is a registered trademark of ROMIL Ltd.