How long do pH buffers remain usable?
Written by
Kiana Okafor
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Knowledge of pH buffer shelf life allows one to avoid errors in measurement and stabilize the calibration conditions for the measurement. I learned this lesson after observing a 0.4 pH error during the testing of a product, which led me to realize that the pH buffer I had purchased had expired. While manufacturers do provide expiration dates on buffers, the conditions under which the buffer is stored and the actual date the buffer is first opened do matter when determining the buffer's shelf life.
Unopened Buffers
- Last until expiration date when stored properly
- Require consistent temperatures below 77°F (25°C)
- Need protection from light in opaque containers
- Maintain accuracy if seals remain intact
Opened Buffers
- Degrade within minutes due to CO₂ absorption
- pH 7 buffers shift fastest losing 0.1 pH/hour
- Discard after 20 minutes of air exposure
- Never reuse bottles after initial opening
Special Formulations
- Low-ionic buffers degrade 300% faster than standard
- TRIS-based buffers last only 10 minutes opened
- Oxygen-free buffers extend usability slightly
- Refrigerated storage slows degradation
The absorption of CO₂ subsequently modifies buffer chemistry rapidly. When opened, buffered solutions at a pH of 7 absorb CO₂, thus forming carbonic acid. As a result of this process, acidification affects the pH, causing a change of up to 0.5 units in one hour. I measure the pH of the buffered solution before each calibration to identify any early degradation.
The longevity of the product is significantly influenced by the type of storage container used. Oxygen-barrier bottles should be utilized for commercial buffers. The most detrimental way to store buffers is by transferring them into other containers, which will shorten their shelf life. I always label bottles with the date and time they were opened and aim to dispose of the contents as soon as possible.
There are visual indicators that indicate buffer use expiration or deterioration. All cloudiness or particles should be discarded immediately, regardless of their age. I always visually inspect the buffer under bright light before using it. pH testing strips are also a quick way to verify a buffer and can sometimes catch subtle changes before the buffer is used.
Buffer handling protocols help prevent waste. I pour small amounts of buffer into secondary containers to minimize exposure to air. I aliquot in 50ml increments to calibrate and discard any excess immediately. This method has cut my buffing costs by 40% while producing accurate results.
Regulatory compliance requires stringent buffer control. The FDA requires documentation of buffer lot numbers and the times of opening. My facility uses barcoded buffers with expiration dates. Audits confirm compliance by reviewing records for buffers used during production.
Read the full article: pH Meter Calibration: Step-by-Step Guide
