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

Abstract

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 degrees 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) +/- in equilibrium (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.