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 having ionic strengths (I = 0.16 molkg -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-Hckel equation. The values of E j for the buffer solution of HEPBS have been obtained from the flowing junction cell measurement. These values of E j 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.