Calix[4]arene containing quinoline as ionophore in ion selective electrodes

Abstract

Two ion selective electrodes (ISEs) containing two new ion selective membranes were prepared. The ion selective membranes consisted of two supermolecules, QN-1 and QN-2, as ionophores. Both structures of ionophores were based on p-tert-butylcalix[4]arene. The structures of ionophores QN-1 and QN-2 comprised one and two quinoline units, respectively, as metal ion receptors. The ion selective membranes also consisted of PVC as a polymer, potassium tetrakis(4-chlorophenyl)borate (KTpClPB) as an ion exchanger, o-nitrophenyloctyl ether (o-NPOE) or dioctyl sebacate (DOS) as a plasticizier. The ability of the ISEs in response to Na+, K+, Ca2+, Mg2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ and Hg2+ was studied. QN-1, the ionophore containing one soft nitrogen and one hard oxygen donors, showed the same selectivity towards Ag+ as QN-2. Both QN-1 and QN-2 exhibited comparable discriminating abilities to interfering Hg2+. However, QN-2 showed much improvement in discriminating abilities to other interfering cations (Na+, K+, Ca2+, Mg2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+) as compared to QN-1. The ISE containing QN-2 as ionophore has, therefore, been selected for further studies. The DOS-plasticized membrane from QN-2 exhibited a near-Nernstian response to silver ion (53.3 ± 1.0 mV decade−1 ) and a linear range of 10−5 to 10−2 M with a detection limit of 8.3 × 107 M. The electrode reversibility was performed by alternatively measuring EMF at two different concentrations, 10-4 and 10-3 M Ag+ and it was found that the EMF signals was restored at the same concentration of Ag+ in every cycle. Therefore, the electrode can be used to measure the Ag+ concentration with excellent reversibility. An application of the fabricated electrode QN-2 in argentometric titration of chloride ion was achieved.