Crown ethers bearing 18C6 unit; Sensory molecules for fabricating pvc membrane lead ion-selective electrodes

Abstract

Crown ethers bearing 18C6 unit 18-crown-6 (18C6), dicyclohexyl18-crown-6 (DC18C6) and dibenzo18- crown-6 (DB18C6) have been examined as ion sensing materials for fabricating lead ion-selective potentiometric sensors. Best performance of the electrode based upon 18C6 ionophore was achieved by using a membrane including 9% ionophore, 30% polyvinyl chloride (PVC), 2% oleic acid and 59% dibutylphthalate (DBP). The optimum composition for the sensors based on DC18C6 and DB18C6 was provided by the compositions: 9%DC18C6, 30% PVC, 1.5% sodium tetraphenyl borate (NaTBP), 59.5% DBP; and 5.9% DB18C6, 29.7% PVC, 2.5% NaTBP and 61.9% DBP, respectively. The linear response range of the electrode based on 18C6 (1 × 10-6-1 × 10-3M) differs from that presented by the DC18C6- and DB18C6-based electrodes (1 × 10-5-1 × 10-2 M). All the sensors were shown rapid response time (<12 s). The detection limit of the electrodes varies as 5.6 × 10-7, 6.3 × 10-6 and 7.1 × 10 -6M, for 18C6-, DC18C6- and DB18C6-based electrodes, respectively. The selectivity of the electrodes towards lead ions over some mono-, di- and trivalent metal ions was evaluated. The lifetime of the electrode based on DC18C6 or DB18C6 ionophores was found to be more than three months, while it was shorter for 18C6-based electrode. The application of the electrodes in aqueous samples was assessed.