On the selection of the optimal plasticizer for calix[n]arene-based ion-selective electrodes: Possible correlation between the ion selectivity and the 'softness' of the plasticizer

Toru Sakaki, Takaaki Harada, Yohko Kawahara, Seiji Shinkai

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19 Citations (Scopus)

Abstract

A criterion for the selection of a suitable plasticizer for calix[n]arene-based ion-selective electrodes is discussed. The cation selectivity of plasticized membranes without the ligand was first measured as a reference. The membranes can be roughly classified into two groups. The first group shows cation selectivity in the order Cs+<Rb+>K+>Na+>Li+. The membranes in the second group are made of phosphorus plasticizers, which show a selectivity in the reverse order. The plasticizers in the first group featured a linear relationship between the dipole moment of the plasticizer (calculated by a PM3 method) and the ratio of cesium selectivity to lithium selectivity. The linear relationship supports the view that the polar membrane which includes a 'soft' plasticizer with a large dipole moment shows selectivity for Cs+, whereas the nonpolar membrane including the 'soft' plasticizer with the small dipole moment shows much lower selectivity for Cs+. Next, 2-fluorphenyl-2′-nitrophenyl ether (FPNPE) which showed the highest Cs+ selectivity and tris(2-ethylhexyl)phosphate (TEHP) which showed the highest Li+ selectivity were mixed in an appropriate ratio to make membranes with a different affinity for 'hard' ions. The metal selectivities of several crown-based and calixarene-based ionophores were examined in these membranes. Although a few exceptions exist, the polar 'soft' membrane is favorable when the interfering metal ion is 'hard", whereas the 'hard' membrane is favorable when the interfering metal ion is 'soft'.

Original languageEnglish
Pages (from-to)377-392
Number of pages16
JournalJournal of Inclusion Phenomena and Molecular Recognition in Chemistry
Volume17
Issue number4
DOIs
Publication statusPublished - Dec 1 1994
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Food Science
  • Chemistry(all)
  • Condensed Matter Physics

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