HEPES hemisodium salt (4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid hemisodium salt) may be used in the preparation of HEPES buffer, which has been described as one of the best all-purpose buffers available for use in biological research. The molecule is zwitterionic at most biological pHs and is most effective as a buffer at pH 6.0 to 8.5.