Polyvinyl chloride-based 18-crown-6, dibenzo18-crown-6 and calix-[6]-arene zinc(II)-potentiometric sensors

Abstract

Polyvinyl chloride (PVC) based membranes of 18-crown-6 (18C6), dibenzo 18-crowen-6 (DB18C6) and calix[6]arene (CAX), as ionophores, with dioctylphenylphosphonate (DOPP), bis(ethylhexyl)sebacate (DOS) dioctyl phthalate (DOP), 2-nitrophenyloctylether (o-NPOE) and didecylphthalate (DDP) as plasticizing solvent mediators are prepared and constructed for the determination of Zn(II). Of the 15 membranes constructed, only the PVC based membranes of DB18C6 and 18C6 ionophores with DOPP, as plasticizer, in the ratio (w/w) PVC:ionophore:DOPP (60:2:120) give the best results in terms of working concentration range (1.0×10−5–1.0×10−1M) with a Nernstian slope of 29.0mV/decade of activity for membrane composed of DOPP+DB18C6(1a) and (1.0×10−5–1.0×10−1M) with a Nernstian slope of 30.0mV/decade of activity for membrane composed of DOPP+18C6(1b). The usable pH range of the sensors is 3.0–8.0, beyond which a drift in potential is observed. The response time of the sensors is ⩽15s with a lifetime of 2months during which they can be used without any measurable divergence. The selectivity coefficient values indicate that the electrode is highly selective for Zn2+ over a number of other cations except Pb2+ and Ag+. The electrodes have successfully been used to determine Zn(II) in real alloys and standard samples with a precision as relative standard deviation (RSD) <2% for each of the cited electrodes. The results obtained by the proposed ISEs are in good agreement with the results obtained by direct flame AAS method.