Buffer Standards for the Physiological pH of the Zwitterionic Compound, ACES, from 5 to 55 °C

摘要

The values of the second dissociation constant, pK2, and related thermodynamic quantities of [N-(2-acetamido)-2-aminoethanesulfonic acid] (ACES) have already been reported over the temperature range 5 to 55 °C including 37 °C. This paper reports the paH values of four chloride ion free buffer solutions and eight buffer solutions with I = 0.16 mol_kg_1, matching closely that of the physiological sample. Conventional paH values for all twelve buffer solutions from 5 to 55 °C are reported. The residual liquidjunction potential correction for two widely used temperatures, 25 and 37 °C, has been made. The flowing-junction calomel cell method has been utilized to measure Ej , the liquidjunction potential. The operational pH values for four buffer solutions at 25 and 37 °C are calculated using the physiological phosphate buffer standard based on the NBS/NIST convention. These solutions are recommended as pH standards in the pH range of 6.8 to 7.2 for physiological fluids.