Medium effects, comparability and predictability of pH-standards in aqueous+organic solvent mixtures: behavior of the (ethylene carbonate+water) and (propylene carbonate+water) systems

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

“…Detailed discussions on mixed aqueous-organic solvent systems can be found elsewhere (see, e.g. [3][4][5][6][7][8]). …”

pH measurements in non-aqueous and aqueous-organic solvents - definition of standard procedures

“…pH(PS) is obtained by extrapolation to m Cl→0 of the straight-line plot of pa H against m Cl . The possibility of altering the order of the two operations, extensively discussed elsewhere [2,3,5,7], depends on the non-linear characteristics of plots of p(a H γ Cl ) against m Cl frequently observed in aqueous-organic mixtures and on the matching, invariably observed, linear behaviour of the dependence of pa H on m Cl , and as confirmed also by the most recent pH data [9] for 0.05 mol kg -1 potassium hydrogen phthalate standard buffer solution in propylene carbonate-and ethylene carbonate-water mixtures.…”

“…Finally, considering the unlimited number of binary solvent mixtures (not to mention ternary systems), it is evident that any recommended procedure, even the most effective, would never satisfy all the user's needs and that experimentally determined standard pH values should also be used to implement and refine appropriate interpolating or (better) predictive [6,9,14] equations.…”

“…Ag |AgCl| buffer S, MCl in Z| glass electrode (9) and subsequent data treatment is formally similar to that described for the primary method. As correctly pointed out elsewhere [12], however, the p.d.…”

“…When a binary system is newly investigated this procedure certainly overcomes the inapplicability of comparison methods, which require prior determination of the pH(PS) of at least one buffer solution. It should, however, be remembered that use of the glass electrode in cell (9) has several conceptual draw-backs: 1. the system is heterosolvental, and the potential of the glass membrane might be irreproducibly affected by this dissymmetry; Fig. 1 Simulated pγ Cl as a function of ionic strength, I, and solvent dielectric permittivity, ε Z , at T=298 K 2. k Z is solvent-dependent, hence cannot be determined by calibration with aqueous buffer solutions; 3. in principle, k and k Z are different, hence p(a H γ Cl ) cannot be defined; and 4. the difference between k and k Z also affects the determination of E 9 0Z from measurement of p.d.…”