Sodium Bicarbonate
Sodium bicarbonate is the most generally used buffer in classical cell culture media and reagents. This buffer improves the pH control of media incubated in a 5-10% CO2 atmosphere and provides cells with carbonate ions that are necessary for the metabolic functions of most cells. Additionally, sodium bicarbonate is non-toxic to cells in culture. Since most pre-mixed powdered media are manufactured without sodium bicarbonate, this buffer must be added in appropriate concentrations during liquid media preparation either as a sterile solution or as a powder prior to filtration.

Atlanta Biologicals offers sodium bicarbonate as a powder and as a 7.5% solution in cell culture grade water.

HEPES
HEPES (N-2-hydroxyethylpiperazine-N’-2-ethanesulfonic acid) is a zwitterionic buffer with a pKa of 7.3 at 37°C. HEPES may be added to cell culture media at a final concentration of 10-25mM to provide additional buffering capacity if required. Media supplemented with HEPES exhibit more effective buffering in the physiological pH range with most cell cultures than media using the normal bicarbonate buffering system alone. However, HEPES should be added in addition to, not instead of, sodium bicarbonate, as it is important to maintain sufficient bicarbonate in the medium for nutritional purposes. Since the buffering capacity of HEPES is independent of the CO2 concentration, it is an ideal buffer for maintaining the pH of cultures outside of the CO2 incubator. HEPES buffered media are resistant to rapid, drastic pH changes, but will not prevent pH shifts entirely. High levels of HEPES can cause cytotoxicity. Concentrations of this organic buffer should be reduced if toxicity is apparent for a specific cell line or primary cell culture.

Atlanta Biologicals offers HEPES as a powder and as a 1M solution in cell culture grade water.