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 × 107 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.
