Silver-Silver Cryptate(2,2) Ion Electrode as a Reference Electrode in Nonaqueous Solvents

Abstract

A silver-silver cryptate(2,2) ion electrode (Ag/0.005 M AgCryp(2,2)ClO₄, 0.005 M Cryp(2,2), 0.05 M Et₄NClO_4- (S)//0.05 M Et₄NClO₄(S)//) was studied with respect to its applicability as the reference electrode in acetonitrile (AN), propylene carbonate (PC), methanol (MeOH), dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF). The apparent formation constant of AgCryp(2,2)⁺ and the potential of the AgCryp(2,2)⁺/Ag electrode vs. ferrocene/ferricinium reference system, respectively, were 7.8 and −422 mV in AN, 15.5 and −400 mV in PC, 9.8 and −253 mV in MeOH, 7.3 and −463 mV in DMSO, and 9.9 and −466 mV in DMF. The exchange current densities of the AgCryp(2,2)⁺/Ag electrode were in the range of (3−5)×10−⁶ A cm^-2 in all the solvents. The electrode potential was not influenced by the total concentration of (AgCryp(2,2)⁺+Cryp(2,2)), provided that the ratio of both species was kept 1:1. The effect of water on the potential was also relatively small. The disadvantages of the silver-silver ion reference electrode especially encountered in PC and DMF were removed with this electrode, and the potential was reproducible and stable enough in all the solvents.