Abstract: The invention provides a solid state reference electrode comprising: a reference element in ionic communication with a composite, the composite comprising a water-permeable polymeric matrix loaded with a solid inorganic salt comprising a reference anion; an electrode surface for contacting an analyte; and a solid ion-exchange material located between the electrode surface and the reference element, the solid ion-exchange material comprising one or more non-interfering ions, wherein in use the solid ionexchange material immobilises one or more interfering ions, when present in solution in the analyte, by exchange with the noninterfering ions.

Abstract: The invention provides a multi-layered electrode for sensing pH, the electrode comprising: a sensing layer on a substrate, the sensing layer comprising at least one proton-sensitive metal oxide, wherein a pH-dependent potential of the multi-layered electrode is measurable via an electrically conductive connection to the sensing layer; a proton-permeable layer covering at least a portion of the sensing layer, the proton-permeable layer comprising at least one electrically insulating proton-conductive metal oxide; and a carbonaceous layer on the proton-permeable layer, the carbonaceous layer comprising amorphous carbon.