Potentiometric performance and interfacial kinetics of neutral ionophore based ISE membranes in interfering ion solutions before and after contact with primary ions

The potentiometric response and the electrochemical impedance spectra of th in PVC based membranes selective to Ca2+ and to Na+ were studied before and after first contact with respective primary ions. The membranes included p otassium tetrakis(p-Cl-phenyl) borate, thus being initially in potassium fo rm. Nearly Nernstian potentiometric responses were obtained in interfering electrolytes before the contact with primary ions, while after the first co ntact the slope of potentiometric curves decreased drastically. However, th e impedance spectra were similar regardless of prior conditioning of the me mbranes, and no evidence for a hindrance towards charge transfer processes was observed, The results suggest that the membrane/solution interface reac tions are reversible both for the primary and the interfering ions, and the contamination of the solutions with primary ions is the only reason for th e lack of Nernstian response in interfering electrolytes.