Potentiometric properties and impedance spectroscopic data of poly(vinyl chloride) membranes containing quaternary ammonium salts of different chemical structure

The influence of the chemical structure of symmetrical and asymmetrical qua ternary ammonium salts (QASs) on the potentiometric and impedance spectrosc opic data of ion-selective poly(vinyl chloride) membranes plasticized with 2-nitrophenyl octyl ether (NPOE) and bis(2-ethylhexyl) sebacate (DOS) was i nvestigated. It was found that the properties of the QAS, e.g. solubility i n the membrane phase and, thus, the difference in the degree of association , influences the membrane characteristics. An increasing number of carbon a toms in symmetrical QASs diminishes the interference of lipophilic anions a nd enlarges the sensitivity to basic ones. The choice of plasticizer is imp ortant for the membrane properties as well, e.g. the influence of lipophili c ions is smaller for DOS membranes in comparison to NPOE ones. Results are discussed from the viewpoint of the difference in free enthalpy of hydrati on and basic properties of the anions. Additionally, the bulk properties of the membranes in dependence of QAS structure were studied by electrochemic al impedance spectroscopy. The magnitude of the specific bulk resistance is governed by the dielectric properties of the plasticizer. Nevertheless, it is shown that QAS structure determines the long-term development of the bu lk resistance. (C) 1999 Elsevier Science B.V. All rights reserved.