Influence of electrode body material on the analytical behaviour of solid-contact ion-selective electrodes

Different materials such as PVC, PTFE, or PEEK are commonly used as the external body of solid-contact ion-selective electrodes (SC-ISEs). So far, the possible effect of these electrode body materials on the analytical behaviour of SC-ISEs has not been considered. In this study, we demonstrate that the selectivity of SC-ISEs can be strongly influenced by the type of the material used as the electrode body. To investigate this effect, different characterization techniques such as potentiometry, optical microscopy, NMR, and FTIR were used. Interestingly, the electrode body material significantly influences the selectivity in the case of bicarbonate SC-ISEs (anionic ISE), while the effect is negligible in the case of potassium SC-ISEs (cationic ISE). Results from NMR and FTIR indicate that some additives or compounds may migrate into the plasticised PVC membrane thereby influencing the selectivity of SC-ISEs. However, one cannot exclude the opposite process where membrane components will diffuse into the PVC electrode body. This can be quite a complex process as not only the chemical composition of the PVC rod would play a role but also its physical properties such as porosity or tortuosity.