Synthesis of aryl ethyne derivatives containing tripodal amine groups and application in prospective copper(II) and cadmium(II) ion selective membrane electrodes

Abstract

PVC membranes for cadmium ion selective electrodes (Cd-ISEs) have been prepared from different types of ionophores. Ionophores I and II obtained from aryl ethyne derivatives as building block have been designed and synthesized in 11% and 40% yields, respectively. Ionophores III contains a calix[4]arene framework. Three ionophores were attached to a number of tripodal amine groups as donor atoms for cation ions, especially cadmium ion. Ionophores II and III can be used as effective ion carriers in membrane electrodes for cations while ionophores I cannot be used due to its decomposition. Compositions of the membranes containing ionophores II and III are optimized by using a constant concentration of the ionophores and varying the amount of ionic additives and plasticizers. The optimized membrane compositions are studied in terms of potentiometric responses, reproducibility, sensitivity and selectivity toward Cd2+ and the detection limit of electrodes. The best characteristics of Cd-ISEs using ionophores II and III were obtained from membrane compositions having 10 mmol kg−1 of ionophores and ionic additive KTpClPB (75 mol% related to the ionophore) incorporating with o-NPOE plasticized PVC membrane (1:2; PVC: o-NPOE by weight). The membranes containing ionophores II and III exhibited a Nernstain response to Cd2+ over a working concentration range of 10-5-10-2 M with a slope of 26.6 ± 0.2 and 30.7 ± 0.1 mV decade-1, respectively. Electrodes containing II and III displayed fast response time in less than 5 seconds and the detection limits were 4.75x10-6 and 3.95x10-6 M, respectively. In addition, the prepared Cd-ISEs showed selectivity toward Cd2+ over other metal ions including of alkali alkaline earth and transition metals. Fe3+, Cr3+ and Pb2+ were found to be strong interfering ions for ionophore II while Fe3+ and Zn2+ were main interfering ions for ionophore III. In addition, the prepared Cd-ISEs can be used to detect Cd2+ in the pH range 4.5-6.0 and gave satisfactory reversibility.