Hydrogen carbonate is an acid salt formed by carbonic acid and contains hydrogen carbonate ions. Most hydrogen carbonates are thermally unstable and decompose into carbonates, carbon dioxide and water. Alkali metal hydrogen carbonate dissolves in water, the aqueous solution is alkaline, reacts with acid quickly to release carbon dioxide gas, and the corresponding normal salt carbonate is obtained by adding alkali.
Animal cell culture medium is alkaline, and a small amount of phenol red indicator is often added to the medium. According to the color change of the indicator, the change of pH value of the medium can be displayed directly. At the beginning of culture, the pH value of the culture medium was 7.4. In the process of culture, because more CO2 and lactic acid are produced with the increase of cell concentration, the pH value will decrease, but it must not be lower than pH 7.0. It is very important to accurately control the pH value, which is generally 6.7-6.9, and its fluctuation range is 0.05-0.9. Although the optimal pH value of many hybridoma cells is about 7.0, when it decreases to 6.8, it will inhibit the growth.
In large-scale culture, there is a pH meter that can be detected at any time. Direct addition of acid or alkali is not suitable for animal cell culture. Hydrogen carbonate buffers are commonly used and CO2 is added to adjust the pH value. The pH value in the culture medium depends on the concentration ratio of CO2 to hydrogen carbonate. The addition of CO2 can reduce the pH value, and the addition of hydrogen carbonate can increase the pH value. However, the buffer capacity of hydrogen carbonate buffer is weak, and the safe way is to control the pH value indirectly by controlling the amount of dissolved oxygen, but increasing the amount of dissolved oxygen will replace CO2 in the culture medium, resulting in the increase of pH value. Therefore, it should be reasonably prepared so as to achieve the purpose of control.
