Coated-wire and composite ion-selective electrodes based on doped poly(pyrrole)

Abstract

Chemically and electrochemically prepared doped poly(pyrrole) has been evaluated as a membrane component for ion-selective electrodes (ISEs). Two types of ISE were prepared: coated-wire electrodes (CWEs) and classical ISEs with heterogeneous membranes. The classical ISE membranes investigated consisted of poly(pyrrole) particles dispersed in a polymer binder; the CWEs were doped poly(pyrrole) films produced by electropolymerization onto platinum wire or glassy carbon rods. Polymerization was carried out in aqueous electrolytes containing chloride, fluoride or nitrate counter anions. The characteristics of the electrodes varied with the electrode type and the conditioning procedure. The CWEs generally exhibited a sub-Nernstian response to the corresponding dopant anion, the actual response depending on polymerization conditions and subsequent conditioning of the electrode. In comparison, the classical ISEs with a heterogeneous membrane of electrochemically prepared poly(pyrrole) showed either reduced sub-Nernstian responses or cationic responses. The classical ISEs with membranes containing chemically polymerized pyrrole exhibited a sub-Nernstian response to the corresponding dopant anion. Electrode failure and poor electrode response appears to be related to the incorporation of cationic sites into the membrane.