A simple way to modify selectivity of sodium sensitive electrodes by using organic conductive crystals

Abstract

An ion-selective membrane is an essential element in the construction of ion-selective electrodes. In this work, some investigations concerned on influence of an ion-selective membrane composition on sodium-selective electrode properties are presented. Several coated-disc sodium-selective electrodes were prepared with the use of sodium ionophore III or sodium ionophore VI, or mixture of these two selective carriers. Membranes with the same compositions were also used to obtain sensors with solid contact transducer layer consisted of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its sodium radical salt (NaTCNQ). In other polymeric membranes, a whole or some part of ionophore was replaced by NaTCNQ in order to assess the effect of its presence on sodium single-piece electrode characteristics. All kinds of prepared electrodes were tested using potentiometric and chronopotentiometric studies, and significant impact of membrane composition on electrode parameters was observed. Among investigated sensors, TCNQ/NaTCNQ-contacted all-solid-state electrodes exhibited the best analytical and electrical performance due to the presence of the intermediate layer, which simplifies the ion-to-electron transduction process between the ion-sensing membrane and the glassy carbon electrode. Exemplary, these electrodes with sodium ionophore III had a close-to-Nernstian slope (58.63 mV/pNa) in the range from 10−5–10−1-M NaCl and revealed detection limit of 10–5.2 M. However, the mixing of sodium ionophores III and VI in one polymeric membrane led to improved sensitivity and limit of detection (58.79 mV/pNa and 10–5.4 M, respectively). The highest capacitance observed for electrodes with TCNQ/NaTCNQ based on intermediate layer was 139 μF.