Synthesis, complexation and use of calix[4]crown-6 as a novel neutral ionophore for the preparation of a selective and sensitive PVC-membrane potentiometric sensor for Ba2+ ion

Abstract

Calix[4]crown-6 (L) was synthesized and the stoichiometry and stability of its complexes with alkali, alkaline earth, Ag+, Tl+ and NH4+ ions were studied conductometrically in acetonitrile solution. The resulting 1:1 Ba2+-L complex was found to be the most stable one among all cation complexes studied. The optimized structures of the ligand and its Ba2+ complex are also reported. Based on the findings, L was used as a suitable ionophore to prepare a PVC-membrane selective electrode for Ba2+ ion. The electrode revealed a Nernstian behavior over wide barium ion concentration 1.0 × 10−6 to 1.0 × 10−3 M with only little trace of 7.1 × 10−7 M. The potentiometric responses were found to be independent of the pH of test solutions in the range of 4.0–10.0. The proposed electrode response time of about 10 s proved to be highly selective for Ba2+ ion over a wide variety of cations including alkali, alkaline earth, transition and heavy metal ions. The sensor could be used for at least three months without any noticeable deviation. The practical utility of the proposed electrode was also examined.