Element profiles in galvanostatically polarized K+-selective all-solid-state sensors with poly(vinyl chloride)-based membranes

The influence of galvanostatic polarization on ion concentration profiles in all-solid-state ion-selective sensors was studied. As a model system K⁺-selective electrode with poly(vinyl chloride)-based membrane, ionophore–valinomycin and polypyrrole doped by chloride ions as ion-to-electron transducer was selected. The ion exchanger—a typical component of ion-selective membrane—was replaced by lipophilic salt: tetradodecylammonium tetrakis(4-chlorophenyl) borate to avoid spontaneous extraction of potassium ions. Potassium, sodium, and chlorine distribution within the sensor phases were studied using laser ablation micro-sampling followed by inductively coupled plasma mass spectrometry measurements. The experiments revealed accumulation of potassium ions in course of cathodic galvanostatic polarization, with concentration decreasing by moving inside the ion-selective membrane. The surface content of K⁺ ions was found to be linearly dependent on applied current. Influence of sequential anodic galvanostatic polarization or open circuit conditioning applied after cathodic polarization revealed only limited recovery of the initial concentration profiles in the membrane.