NASICON membrane used as Na+-selective potentiometric sensor in steady state and transient hydrodynamic conditions

A commercial NASICON pellet was tested for Na+-selective electrode in batch as well as in flow conditions, using two different hydrodynamic regimes: steady state and flow injection. The optimal hydrodynamic conditions to operate a homemade flow-trough cell (of wall-jet type) were established by performing amperometric measurements at a graphite electrode with the ferro/ferricyanide redox couple. Among the investigated supporting electrolytes (BaCl2, CaCl2, TEBA, TEAC, TRIS and HEPES), used for batch electrode calibration to Na+, TEAC showed the smallest interference versus Na+ together with a low limit of detection (9.2±0.5×10−5 M). A comparison between the main analytical parameters (sensitivity, limit of detection and selectivity versus Li+, K+ and H+) observed for batch, steady state flow (SSF) and flow injection (FI) measurements showed that: (i) no significant differences were observed between batch and SSF conditions; (ii) in FI mode the sensitivity was higher, the limit of detection was slightly increased and, in the presence of BaCl2, the selectivity for the proton interference was improved.