Prepared standard SOLUTIONS should be stored in hermetically sealed, high-quality HARD glass or polyethylene containers. The pH value of the standard solution may change(Note) after long-term storage. Before using a standard solution that has been stored for a long time after preparation, compare its pH with that of a freshly prepared standard solution and ensure that they are the same.

Moreover, a pH standard solution must never be used once it has been LEFT to the atmosphere.

Note: For example, borate and carbonate pH standard solutions may absorb CO2 and other substances in the atmosphere and their pH values may decrease.

Prepared standard solutions should be stored in hermetically sealed, high-quality hard glass or polyethylene containers. The pH value of the standard solution may change(Note) after long-term storage. Before using a standard solution that has been stored for a long time after preparation, compare its pH with that of a freshly prepared standard solution and ensure that they are the same.

Moreover, a pH standard solution must never be used once it has been left to the atmosphere.

Note: For example, borate and carbonate pH standard solutions may absorb CO2 and other substances in the atmosphere and their pH values may decrease.