HEPES

HEPES is used in many media because it has more buffering capacity than sodium bicarbonate at physiological pH (7.2 – 7.4) at 37°C. Sodium bicarbonate is nutritionally necessary for most cells, so HEPES should be added in addition to, not in place of, sodium bicarbonate. It is commonly added at 10 – 25 mM concentrations (higher levels may cause cytotoxicity).