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

The values of the second dissociation constant pK(2) 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 pa(H) values of four chloride ion free buffer solutions and eight buffer solutions with I = 0.16 mol·kg (-1), matching closely to that of the physiological sample. Conventional pa(H) values for all twelve buffer solutions from 5 to 55°C, are reported. The residual liquid junction 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 E(j) , the liquid junction potential. The operational pH values for four buffer solutions at 25 and 37°C are calculated using the physiological phosphate buffer standard based on NBS/NIST convention. These solutions are recommended as pH standards in the pH range of 6.8 to 7.2 for physiological fluids.