What is the shelf life of a buffer solution? How long does it last after the bottle is opened?

Yokogawa's buffer solutions have a guaranteed shelf life of 12 months from the date of shipment. The exception to this is the sodium buffer solutions used to calibrate the differential pH sensors (part numbers K1520BF, K1520BG, K1520BH, K1520BJ and K1520BK). The shelf life of the sodium buffer solutions is 6 months from the date of shipment.

For accuracy, it is recommended that a buffer should not be used for more than one month after opening. Buffers should be stored in tightly sealed, preferably air-tight bottles made of polyethene or borosilicate glass. Buffers should not be returned to the bottles once removed.

When the bottle is open, the electrolyte is exposed to air. Air contains 0.04% CO2 and this gas is absorbed by the buffer solution as Carbonic acid which causes the pH of the solution to drop. Therefore the pH 4.01 buffer and pH 6.86 buffer are not as sensitive and the buffer quality does not degrade as strongly when the bottle is opened. The alkaline buffers are much more sensitive to exposure to air and the pH will continue to drop. So it is particularly important that the pH 9.18 buffer be kept in a closed bottle and cannot be kept long after opening.