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.
Key WordsBuffers TAPS liquid junction ionic strength emf zwitterions pH acidity function
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