Examining the Buffer Standards for Physiological pH of the Buffer N-(2-Acetamido)-2-aminoethanesulfonic Acid in the Range 5°C to 55°C

The zwitterionic amino acid buffer solutions have been previously studied by different authors for the purpose of pH measurement control in the physiological range of pH. The goal of these studies is to provide pH values for the N -(2-acetamido)-2-aminoethanesulfonic acid (ACES). Electromotive force (emf) measurements of the Cell Pt(s), H2(g)|ACES(m₁) + NaACES(m₂) + NaCl(m₃) | AgCl, Ag(s) have been carried out from 5oC to 55oC. The agreement of pH values between the two calculated (extended Debye-Hückel and liquid junction correction) is excellent. Two buffer solutions without the chloride ion and seven buffer solutions with NaCl, at an ionic strength ( I = 0.16 mol.kg₋₁) similar to that of physiological fluids, have been studied. The pH values for these buffer solutions have been evaluated in the temperature range of 5oC to 55oC using the extended Debye-Hückel equation of the Bates-Guggenheim convention. Values of the residual liquid junction potential between the ACES solutions and the saturated KCl calomel electrode solution have been estimated at 25oC and 37oC from the previously determined Ej values using the flowing junction cell to determine the operational pH values at 25oC and 37oC. These ACES buffer solutions are recommended as secondary standard reference solutions for pH measurements in the range of physiological application at I = 0.16 mol.kg-1. The main application of these pH data is to establish a unified pH scale applicable to a wide range of ionic strengths for practical pH measurements.