Standard electromotive force of the H2---AgCl;Ag cell in 30, 40, and 50 mass% dimethyl sulfoxide/water from −20 to 25 °C: pK2 and pH values for a standard “Bicine” buffer solution at subzero temperatures

The establishment of the pH (designated pH*) of a standard buffer solution suitable as a pH reference in 30, 40, and 50 mass% dimethyl sulfoxide (DMSO)/H₂O mixtures at temperatures in the range −20 to 0 °C is reported. The buffer material selected was the ampholyte Bicine (N,N-bis(2-hydroxyethyl)glycine), and the reference standard consists of equal molal quantities of Bicine and its sodium salt. The assignment of pH* values rests on measurements of the emf of cells without liquid junction, Pt;H₂(g, 1 atm) ¦Bicine, Na Bicinate, NaCl ¦AgCl;Ag, and the pH* was derived from a determination of K₂, the equilibrium constant for the dissociation process (Bicine) ^± (Bicinate)⁻ + H⁺. The standard emf in the DMSO/H₂O solvents at subzero temperatures was determined from emf measurements of the cell with solutions of HCl replacing the buffer-chloride mixture.