Proper storage of your
pH buffer solution

Treat your pH buffer solution with care, it is your measurement reference.

Shelf-life

The typical shelf-life for technical buffers is 2 years unopened and 3-6 months open. However, this is not valid for alkaline buffers (pH buffer 10 or higher). Alkaline solutions will change their pH noticeably when they come into contact with carbon dioxide in the air. The typical shelf-life for alkaline buffers is 1 month open.

Make sure you check the expiration date for your pH buffer solution. Look at the label of the package or at the related certificate of analysis. Do not use a buffer if the expiration date has passed.

Note: The expiration date is for an unopened container.

Container

Keep your pH buffers in tightly closed containers.

Storage

Store the buffers at room temperature, 15 to 30 °C (60 to 90 °F), or refrigerated, 2 to 8 °C (35 to 45 °F).

For alkaline buffers, it's recommended to put the bottles in the refrigerator but not if you have something in the refrigerator which produced a carbon dioxide atmosphere. At lower temperatures the evaporation of the water in the buffer is slower than at higher temperatures, which help to remain the concentration of the buffer constant for a longer period of time.

When a pH buffer is stored refrigerated, it is recommended to allow the buffer to come to room temperature prior to use. Avoid storage close to a window or to a heat source.

Temperature influence

Temperature plays an important role as regards sample, buffer and pH electrode characteristics. For commercial calibration solutions, the pH values are listed in a table as a function of temperature. These tables are usually printed on the packaging or enclosed as a package insert.


Automatic pH buffer recognition

Most modern pH meters have an automatic calibration feature. pH and temperature values for commonly used commercial buffers are stored into the memory of the pH meter. With this information, the pH meter will be able to automatically compensate for temperature variations.

However, it is important to choose the right buffer in the meter settings, and that the pH meter knows the actual temperature of the calibration solution. The obvious choice is to select a pH electrode with built-in temperature sensor. Using an external temperature sensor is also an alternative even not as convenient as a pH sensor with an integrated temperature sensor.


High measurement accuracy

Even your pH meter has an automatic temperature compensation feature, to achieve high measurement accuracy, the temperature difference between the calibration buffer and the measured medium should be minimized as much as possible, see "How to decrease the offset error". However, a temperature difference of 2 to 5°C ( 4 to 9°F) will be acceptable in most cases. Using hot buffers can be difficult, and precautions are necessary.




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