ANION RESPONSE CHARACTERISTICS OF AN ELECTRODE BASED ON PLASTICIZED POLY(VINYL CHLORIDE) MEMBRANE WITHOUT ADDED ION-EXCHANGER

The potential response of an electrode, based on an o-nitrophenyl octyl ether (o-NPOE)-plasticized PVC membrane without added ion exchanger, to alkyl sulfate, alkanesulfonate, alkylcarboxylate ions and to several hydrophobic anions was investigated. The electrode exhibits the Nernstian response to alkyl sulfate ions having more than ten carbon atoms in alkyl chains. For alkanesulfonate ions, the electrode shows the Nernstian response to dodecylbenzensulfonate and di-2-ethylhexylsulfosuccinate ions, but does not to ions with less than eleven carbon atoms in alkyl chains. For alkylcarboxylate ions with seven to eleven carbon atoms in alkyl chains, the electrode does not show the Nernstian response, but does to tetraphenylborate and 8-anilino-1-naphthalenesulfonate ions. In order to correlate the response characteristics of the o-NPOE-plasticized PVC membrane electrode to the anionic entities with the hydrophobicity of the ions, the selectivity coefficients of an electrode based on an o-NPOE-plasticized PVC membrane containing trioctylmethylammonium chloride as an ion-exchanger was measured, because hydrophobicity of ions is related to the partition properties of ions between an aqueous solution and the electrode membrane. As a result, the o-NPOE-plasticized PVC membrane electrode was found to show the Nernstian response to hydrophobic anions with a selectivity coefficient of more than 10(5.5). The potential response of the electrode, based on the PVC membrane plasticized with o-NPOE derivatives, to dodecyl sulfate ion was also investigated. The best plasticizer among o-nitrophenyl phenyl ether and o-nitrophenyl alkyl ethers (C8, C10, C-12 and C-14) for the dodecylsulfate ion-selective electrode in terms of linear response range and sensitivity was o-NPOE.