Abstract:
Three types of ionophores were designed and synthesized with different number of side-arms, linkers and building blocks, and the effects of their structures on anion sensing properties were then comparatively examined. Ionophore I was synthesized in 73% yield by attaching tripodal amine mononuclear Cu(II) complex directly to the anthracene, while two units of such complex were connected to the p-tert-butylcalix[4]arene with 2-alkoxybenzyl and amide linkers to give ionophores II and III in 42 and 58% yield, respectively. The polymeric membrane sensors containing these ionophores were fabricated and then the sensitivity, selectivity, optimal membrane composition, as well as the important characteristics of electrodes were then explored by varying types and amounts of ion exchangers. The potentiometric investigations indicated that ionophore I could not function properly as an anion carrier due to its low lipophilic single-sided arm structure in membrane electrodes. On the other hand, ionophores II and III exhibited good sensitivity and selectivity toward iodide even in the absence of ion exchangers, resulting from the dinuclear Cu(II) complexes as an effective ion-carrier unit, providing a suitable cavity for iodide. The best iodide-selective electrode was achieved when using ionophore II (10 mmol kg-1) in the presence of 25 mol% of tridodecylmethylammonium chloride (TDMACl) anion exchanger related to the ionophore incorporated in the o-NPOE plasticized PVC membrane, with the Nernstian slope of -54.9 ± 0.2 mV decade-1 of iodide response, the linear working range from 10-5 to 10-2 M, the fast response time less than 5 s, and the limit of detection of 3.3 10-6 M. UV-Visible spectrophotometric studies were also carried out and the spectral shift was observed to affirm the interaction between ionophore and iodide. Moreover, this electrode could be used over a wide pH range of 4.7-8.6 with great reversibility, and also applied to determine the concentration of iodide in the real water samples, mineral water and tap water, with satisfactory recoveries.
