Characterization of Lithium Sulfate as an Unsymmetrical-Valence Salt Bridge for the Minimization of Liquid Junction Potentials in Aqueous-Organic Solvent Mixtures

The transference no. [t] of lithium sulfate in acetonitrile/water and methanol/water solvent mixts. was studied by measuring the emf. of transference cells: Pb(Hg)|PbSO4|Li2SO4 (m2)||Li2SO4 (m1)|PbSO4|Pb(Hg), Hg|Hg2SO4|Li2SO4 (m2)||Li2SO4 (m1)|Hg2SO4|Hg, and LixHg1-x|Li2SO4 (m1)||Li2SO4 (m2)|LixHg1-x, to evaluate Li2SO4 as an unsym. salt bridge for minimization of liq. junction potentials in potentiometric applications. In water, Li2SO4 is nearly as good a salt bridge as KCl; this effectiveness was verified in a pH-meter cell using various aq. pHS stds. In acetonitrile/water solvents contg. 0.09 wt. fraction of acetonitrile at 298.15 K, Li2SO4 shows exact ionic equi-transference, obeying the general condition t+/z+ = t-/|z-|. The Li2SO4 salt bridge can be used for simple insertion between electrolyte solns. to minimize the liq. junction potential, as the outer component of a double-bridge arrangement of any ref. electrode, or, in sulfate-reversible ref. electrodes as the supporting and bridge electrolyte. The operation potential of the Hg|Hg2SO4|2 m Li2SO4 ref. electrode in aq. solns. is 0.6326 V at 298.15 K.