Response behavior of poly(vinyl chloride)- and polyurethane-based Ca(2+)-selective membrane electrodes with polypyrrole- and poly(3-octylthiophene)-mediated internal solid contact

The potentiometric response behavior of Ca(2+)-selective poly(vinyl chloride) (PVC) and polyurethane (PU) membranes with different inner contacts has been compared. Evidence for the formation of a water film between membrane and internal contact and, hence, a less than optimal lower detection limit have been found for membranes directly in contact with bare Au or with polypyrrole generated by electropolymerization in the presence of KCl. A significantly better behavior is shown by membranes with polypyrrole prepared in the presence of potassium hexacyanoferrate. Best performances have been obtained with solvent-cast poly(3-octylthiophene) as the internal contacting layer. As compared with the PVC membranes, those with PU had a significantly worse performance throughout.