How to choose the right biological buffer
forward from: https://www.hopaxfc.com/en
Choosing the right biological buffers for your experiments can be a quite challenging task. With so many options available (Hepes, Mops, Tris, Bis-Tris, and so on) it is easy to be confused.
Knowing about these challenges, Hopax prepared a short list to remind you of some important points to consider when choosing buffer salts for your research.
1. The buffering range
Each buffer has a pH range in which the buffering capacity is the highest. This capacity is usually determined by the pKa of the buffer. You must choose a buffer that has a pKa value near the middle of the range required (in general, it is recommended to use a buffer with a pKa value that is at least within one pH unit of the target pH).
2. pH changes during the experiment
It is important to consider whether the pH is likely to increase or decrease during your experiment. If you expect the pH to increase, you must choose a buffer with a pKa a little bit higher than the optimum at the beginning of the experiment. The same goes for the opposite situation: if you are expecting you pH value to decrease, choose a buffer with a lower pKa.
3. The buffer concentration
The concentration of the buffer must be adjusted in order to have sufficient capacity for the experimental system. In sum, if the concentration of a buffer is too low, it will not be able to stabilize the solution’s pH. Conversely, if the concentration is too high, the buffer is very likely to affect the experiment. In general, it is recommended to use concentrations higher than 25 mM.
A concentration of 25–100mM is usually recommended for systems that don’t actively exchange hydrogen protons. For systems in which proton exchange is expected to happen, it is recommended to use a buffer concentration that is 20x higher than the molarity of the protons being exchanged.
When preparing a buffer solution, remember to make the solution at a concentration that you intend to use.
4. The temperature changes
The pH of a buffer solution has to be set up according to the temperature at which the experiment will be performed. The temperature affects directly the pKa of a buffer and consequently the pH and the buffering capacity of a system. This situation can be very critical in biological systems in which an accurate hydrogen ion concentration is required for reaction systems to operate with maximum efficiency.
The pKa of some buffers, such as PIPES, are not very sensitive to temperature changes, however, other options like TRIS, ACES, TAPS, TES or Tricine can be more affected by these changes.
The chart below presents the approximate pKa variations according to the temperature of Hopax’s biological buffers:
Read more: http://www.hopaxfc.com/en/blog/how-to-choose-the-right-biological-buffer
