Buffer Standards for the Physiological pH of N-(2-Hydroxyethyl) piperazine-N'-4-butanesulfonic Acid (HEPBS) from 5 to 55 °C

The pH values of six buffer solutions of equal compositions on the molal scale and eight buffer solutions hav- ing ionic strengths (I = 0.16 mol·kg -1 ) similar to the concentration of blood plasma have been evaluated at 12 temperatures from 5 to 55 °C using the Bates-Guggenheim convention and extended Debye-Huckel equation. The values of Ej for the buffer solution of HEPBS have been obtained from the flowing junction cell measurement. These values of Ej have been used to ascertain the operational pH values at 25 and 37 °C for HEPBS buffer solution. The pH values at 25 and 37 °C are 7.415 and 7.395, respectively, for physiological phosphate buffer solutions. The zwitterionic buffer HEPBS was shown to be useful as a secondary pH standard in the region close to that of blood serum.