HEPES (N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid) is widely used as a buffering agent in cell culture media. The zwitterion possesses a pKa(1) of 3 and a pKa(2) of 7.5 with useful pH ranges of 2.5-3.5 and 6.7-8.6. In comparison with bicarbonate buffer systems, HEPES is better in maintaining physiological pH despite changes in CO2 concentrations resulting from cellular activity. HEPES is suitable for many cell culture systems as it is membrane impermeable and has limited effect on biochemical reactions.
Appearance: Clear colourless solution.