HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic acid) provides an alternative to the use of bicarbonate for buffering because it does not require elevated levels of CO2

Unlike the low pKa of bicarbonate, HEPES has a pKa of 7.66 making it a much stronger buffer in the pH 7.2-7.6 range than bicarbonate buffer. Potential disadvantages of HEPES include toxicity over 100 mM and lack of nutritive value to the cell.