IMPEDANCE SPECTROSCOPIC STUDY ON SINGLE-PIECE ALL-SOLID-STATE CALCIUM-SELECTIVE ELECTRODE BASED ON POLYANILINE

Single-piece all-solid-state calcium-selective electrodes (CaSPEs) hav e been studied with impedance spectroscopy. The molar ratio (y) of the protonic acid, bis(2-ethylhexyl)hydrogenphosphate, to a repeat unit o f polyaniline (PANI) was y = 0.50. The protonation was performed both at 25 and 110 degrees C. Impedance measurements were used to study the electronic and ionic processes in the CaSPE membranes, The results we re compared with a calcium coated-wire ion-selective electrode (CaCWE) . The bulk resistance of the CaSPEs decreases with PANI concentrations up to 10% (m/m), owing to improved ionic mobility in the CaSPE membra nes. The charge transfer at the substrate/membrane interface was found to be facilitated by incorporation of PAM in the electrode matrix, PA M also stabilizes the bulk resistance of the CaSPEs compared to the Ca CWE. Two types of membranes were studied: (i) 'wet' membranes that had been in contact with an aqueous 0.1 mol dm(-3) CaCl2 solution and (ii ) 'dry' membranes. The obtained impedance spectra were fitted to equiv alent circuits describing the CaSPE system.