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The values of the second dissociation constant, pK 2 , and related thermodynamic quantities of 3-[(1,1-dimethyl-2-hydroxymethyl)amino]-2-hydroxypropanesulfonic acid (AMPSO) have already been reported in previous investigations at 12 temperatures over the temperature range (278.15 to 328.15) K, including 310.15 K (J. Solution Chem. 1997, 26, 309-317). This paper reports the results for the pH of nine buffer solutions free of the chloride ion with compositions: (a) AMPSO (0.04 mol+ NaAMPSO (0.02 mol • kg -1 ); (f) AMPSO (0.06 mol • kg -1 ) + NaAMPSO (0.03 mol • kg -1 ); (g) AMPSO (0.08 mol • kg -1 ) + NaAMPSO (0.01 mol • kg -1 ); (h) AMPSO (0.08 mol • kg -1 ) + NaAMPSO (0.02 mol • kg -1 ); and (i) AMPSO (0.08 mol • kg -1 ) + NaAMPSO (0.08 mol • kg -1 ). The remaining 13 buffer solutions (j to v) have saline media of the ionic strength I ) 0.16 mol • kg -1 , matching closely to that of the physiological sample. Conventional pa H values, designated as pH(s), for all nine buffer solutions (a to i) without the chloride ion and thirteen buffer solutions with the chloride ion (j to v) at I ) 0.16 mol • kg -1 from (278.15 to 328.15) K have been calculated. The operational pH values for six buffer solutions at (298.15 and 310.15) K have been determined based on the difference in the values of the liquid junction potentials between the blood phosphate standard and the experimental buffer solutions. Five of these buffers are recommended as standards for the physiological pH range 7.5 to 8.5.

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The values of the second dissociation constant, pK 2 of N-(2-hydroxyethyl) piperazine-N'-2-ethanesulfonic acid (HEPES) have been reported at 12 temperatures over the temperature range 5 to 55°C, including 37°C. This paper reports the results for the pa H of eight isotonic saline buffer solutions with an I = 0.