Buffer standards for the physiological pH of N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES) from (278.15 to 328.15) K

This paper reports the results for the pH of six buffer solutions free of chloride ion with compositions: (a) BES (0.03 mol kg−1) + NaBES (0.09 mol kg−1); (b) BES (0.02 mol kg−1) + NaBES (0.04 mol kg−1); (c) BES (0.04 mol kg−1) + NaBES (0.08 mol kg−1); (d) BES (0.04 mol kg−1) + NaBES (0.04 mol kg−1) (e) BES (0.05 mol kg−1) + NaBES (0.05 mol kg−1); and (f) (0.06 mol kg−1) + NaBES (0.06 mol kg−1). The remaining eight buffer solutions (g)–(n) have saline media of the ionic strength I = 0.16 mol kg−1, matching closely to that of the physiological sample. Conventional paH values, designated as pH(s), for all six buffer solutions (a)–(f) without the chloride ion and eight buffer solutions with the chloride ion (g)–(n) at I = 0.16 mol kg−1 from (278.15 to 328.15) K have been calculated. The operational pH values for five buffer solutions at T = 298.15 K and T = 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 secondary standards for the physiological pH range 7.5–8.5.