In our biochemical experiments, such as Trinder's reaction of chromogen substrate, acridine ester of luminescent substrate and various enzyme reactions, we use biological buffers, such as bicine, Tris, mops, and the most basic acetate and phosphate buffer systems. It can be said that as long as there are pH requirements for the reaction environment, buffers are needed in the system.
Buffer in delivery
The reason why the buffer solution can adjust pH is that it is a weak electrolyte, which is partially dissociated in the solution and partially exists in the form of molecules, and does not show acidity and alkalinity. Its molecules form a dynamic equilibrium with their ionic conjugated acids or bases (pH = PKA + LG, dissociated concentration is higher than that of the non dissociated concentration). If the pH of the system changes, the sub dynamic equilibrium will move to reach a new equilibrium, thus adjusting the pH.
The effective buffer range of a buffer system is usually in the range of two pH units with pKa value as the midpoint, that is, the effective pH range of the buffer = pKa ± 1. Therefore, when the pH of the buffer solution is equal to the pKa of the buffer, the buffer capacity is the largest. If we want to design a new buffer system, we only need to find out and select the buffers whose pKa value is equal to the required pH value.
In biochemical experiments, there are many commonly used biological buffers. Phosphate is the most widely used and basic buffer in biochemical research. Phosphoric acid is a ternary acid. Because they are secondary dissociation and have two pKa values, the pH range of the buffer prepared with them is the widest, and potassium salt is better than sodium salt, because sodium salt is difficult to dissolve at low temperature and potassium salt is easy to dissolve, but if SDS is prepared- The buffer solution of polyacrylamide gel electrophoresis can only use sodium phosphate instead of potassium phosphate, because SDS (twelve alkyl sulfate) will produce insoluble twelve alkyl potassium sulfate with potassium salt.
Phosphate is easy to be prepared into various concentrations of buffer solution, suitable for a wide range of pH, pH is less affected by temperature, pH change after dilution is small, and pH change after ten times dilution is less than 0.1. However, in the solution system with metal ions, phosphoric acid system will associate with common Ca ions, Mg ions and heavy metal ions to form precipitation.
The Tris buffer produced by us has been used more and more in biochemical research, and has a tendency to exceed phosphate buffer. For example, Tris buffer has been used in SDS- polyacrylamide gel electrophoresis, and phosphate is rarely used. The ACD solution used in our PrP blood collection vessel needs sodium citrate and citric acid to adjust the pH. the citrate here not only regulates the osmotic pressure, but also acts as a buffer. It is also a ternary acid like phosphoric acid.
