Buffer Standards for the Physiological pH of the Zwitterionic Compound, TAPS, From 5 to 55 ∘C

The values of the second dissociation constant, pK ₂, and related thermodynamic quantities of N-[tris(hydroxymethyl)methyl-3-amino]propanesulfonic acid (TAPS) have already been reported at 12 temperatures over the temperature range 5–55 ^∘C, including 37 ^∘C. This paper reports the results for the pH of five equimolal buffer solutions with compositions: (a) TAPS (0.03 mol⋅kg⁻¹) + NaTAPS (0.03 mol⋅kg⁻¹); (b) TAPS (0.04 mol⋅ kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹); (c) TAPS (0.05 mol⋅kg⁻¹) + NaTAPS (0.05 mol⋅kg⁻¹); (d) TAPS (0.06 mol⋅kg⁻¹) + NaTAPS (0.06 mol⋅kg⁻¹); and (d) TAPS (0.08 mol⋅kg⁻¹) + NaTAPS (0.08 mol⋅kg⁻¹). The remaining eight buffer solutions consist of saline media of the ionic strength I = 0.16 mol⋅kg⁻¹, matching closely to that of the physiological sample. The compositions are: (f) TAPS (0.04 mol-kg⁻¹) + NaTAPS (0.02 mol-kg⁻¹) + NaCl (0.14 mol⋅kg⁻¹); (g) TAPS (0.05 mol⋅kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (h) TAPS (0.6 mol⋅kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (i) TAPS (0.08 mol⋅kg⁻¹) + NaTAPS (0.06 mol⋅kg⁻¹) + NaCl (0.10 mol⋅kg⁻¹); (j) TAPS (0.04 mol⋅ kg⁻¹) + NaTAPS (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (k) TAPS (0.05 mol⋅kg⁻¹) + NaTAPS (0.05 mol⋅kg⁻¹) + NaCl (0.11 mol⋅kg⁻¹); (l) TAPS (0.06 mol⋅kg⁻¹) + NaTAPS (0.06 mol⋅kg⁻¹) + NaCl (0.10 mol⋅kg⁻¹); and (m) TAPS (0.08 mol⋅kg⁻¹) + NaTAPS (0.08 mol⋅kg⁻¹) + NaCl (0.08 mol⋅kg⁻¹). These buffers are recommended as a pH standard for clinical measurements in the range of physiological application. Conventional pH values, designated as pH(s), for all 13 buffer solutions from 5 to 55 ^∘C have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 ^∘C for buffer solutions, designated above as (b), (c), (d), (e), (j), (l), and (m); have been determined based on the difference in the values of the liquid junction potentials between the accepted phosphate standard and the buffer solutions under investigation.