Synthesis and application of tetrazole di- and triamide derivatives in ion-selective membrane electrodes

A number of tetrazole diamides (1–9) and triamides (10–11) have been synthesized and applied as ion carriers in ion-selective membrane electrodes. Their selectivity and sensitivity were studied towards alkali, alkaline earth, transition and heavy metal cations. It was found that membranes doped with 3 and 2-nitrophenyl octyl ether (o-NPOE) exhibit an almost theoretical Nernstian response for NH4+ over relatively wide concentration range. Electrodes with ionophores 4 and 5 with bis(1-butylpentyl)adipate (BBPA) show high affinity towards Cd2+; another diamide with two plasticizers exhibits good selectivity for Pb2+ ions. The best ionophores for Pb2+ ions proved to be tren-based triamides, having aryl groups substituted in para and meta position with tetrazole rings. They were suitable for use in aqueous solution in a wide range of pH 2–10 and had a fast response time t95 < 20 s. The electrode with ionophore 11 containing o-NPOE has a wide linear range and good selectivity for Pb2+ ions over Na+ ions (log KPb,Na = –4.39). The relation between the carrier structure and electrode properties has been discussed.