CONDUCTIVE EPOXY-GRAPHITE COMPOSITE AS A SOLID INTERNAL REFERENCE IN A NASICON-BASED SODIUM ION-SELECTIVE ELECTRODE FOR FLOW-INJECTION ANALYSIS

A solid-state conductive polymer composite is proposed as a substitute for the internal liquid reference in a sodium sensor. Epoxy-graphite is used as the composite and NASICON as a sensitive membrane. The abse nce of a liquid internal solution allows the straightforward construct ion of these transducers in various shapes and dimensions. This is pos sible because of the use of an easily moldable plastic support. The co nductivity of the epoxy-graphite composite and the electrochemical beh aviour of the NASICON/conductive epoxy interface were characterized by impedance spectroscopy. The stability and reproducibility of the elec trode potential were studied. Different compositions of the reference system were tested. An all-solid-state, now-through, tubular sodium se nsor based on a NASICON membrane has been evaluated. The construction of a miniaturized sensor is described and its application to flow-inje ction analysis is reported.