Resistance measurements as a simple diagnostic tool for ion‐selective electrode performance

Recently, potentiometric sensors have found numerous applications involving on‐line monitoring in flow systems [1–4]. With trends toward the use of multielectrode arrays and electrode miniaturization, simple diagnostic tests for the routine assessment of device performance will become increasingly important. In this work, we present the possibility of using dc resistance measurements for this purpose. Mini‐sodium‐selective electrodes with polyvinyl chloride (PVC) membranes incorporating the ionophore methyl p‐t‐butylcalixaryl acetate [4, 5] were constructed, and a gradual increase in resistance with lifetime was observed. A lifetime mimicking study was set up in which leaching of the active components from the membrane was simulated by a series of dilutions, and the effect on overall electrode performance was monitored at each stage. Complete electrode malfunction has been shown to occur abruptly when the active membrane component concentration falls below a critical level. Electrode failure is accompanied by a sharp increase in membrane resistance.