Emulsion Doping of Ionophores and Ion-Exchangers into Ion-Selective Electrode Membranes

Ion-selective electrodes (ISEs) are widely used analytical devices to selectively measure ionic species. Despite significant advances in recent years, ion-selective membranes are still mostly prepared in the same manner, by preloading the selective components into a solvent that is subsequently cast into a membrane or film. This paper describes an alternative method to prepare ISE membranes by mass transfer of the sensing components from an emulsion phase. Specifically, blank (undoped) plasticized poly(vinyl chloride) (PVC) membranes mounted into an electrode body are immersed into an aqueous solution containing analyte ions and an appropriate emulsion of the desired sensing components to allow their transfer into the membrane. The concept is demonstrated with conventional membrane electrodes containing an inner solution as well as all-solid-state electrodes. It is shown to be universally useful for the realization of ISEs for K⁺, Na⁺, Ca²⁺, and NO₃^-.