A cryptate reference electrode for ionic liquids

The cryptate electrode (Ag/Ag(+)222), prepared by immersing silver wire in a solution of silver(I) salt and the cryptand 222 (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) in ionic liquids have been studied. The potential of the electrode is stabilized by the equilibrium of the Ag+ ion complexation by the cryptand, similarly to the potential stabilization by the ionic product of slightly soluble salts, used in aqueous electrodes of the second kind. The Ag/Ag(+)222 cryptate electrode (concentration of the cryptate was much higher than the silver(I) cation concentration, [222] > [Ag+]) may be used as a reference electrode in room temperature ionic liquids. The potential of the Ag/Ag(+)222 electrode is less sensitive to the presence of impurities, such as halides or water, in comparison to the Ag/Ag+ electrode. After anodic or cathodic polarization, the potential of the Ag/Ag(+)222 electrode comes back to the initial open circuit potential quickly. Preparation of the Ag/Ag(+)222 reference electrode is very easy: a silver wire is immersed in a solution of Ag+ salt and cryptand 222 (both available commercially) in the ionic liquid under study.