The second dissociation (pK2) of the zwitterionic buffer POPSO and the pH of its buffer solutions have been studied in the temperature range 278.15 – 328.15 K. Experimental emf measurements have been made using the Harned cell without liquid junction of the type: Pt, H2 (g, 1 atm) | Na3POPSO (m1) + Na4POPSO (m2) + NaCl (m3) | AgCl, Ag. The pK2 values and the thermodynamic quantities (∆G°, ∆H°, ∆S°, and ∆Cp°) will be reported at 278.15, 298.15, 310.15 and 328.15 K. The pH values for 4 buffer solutions at equimolar concentrations as well as at ionic strength (I = 0.16 mol•kg-1) matching those in physiological fluids have been determined from (278.15 – 328.15) K. The Bates –Guggenheim convention and the Pitzer equation have been used to calculated the single ion activity coefficient chloride ion, of γcl. The pK2 of POPSO at 298.15 K and 310.15 K are 7.8029 and 7.6628, respectively. The pH values of buffer solutions (I = 0.08 mol•kg-1) at 298.15 K and 310.15 K are 8.0438 and 7.9281, respectively. This physiological buffer will be recommended to fulfill the need for a new physiological primary pH standard in the studies of biomedicine.

Standard buffer POPSO for use in the physiological pH range

249th National Meeting (2015)

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