Ion-selective electrode for transmembrane pH difference measurements

A triethylammonium-sensitive electrode was constructed using sodium tetraki s[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate as an ion-exchanger an d benzyl 2-nitrophenyl ether as a solvent mediator in a poly(vinyl chloride ) membrane matrix and was used to determine the pH difference across a cell membrane. The method is based on monitoring of the pH gradient-induced upt ake of triethylammonium in situ. The triethylammonium electrode exhibited a near-Nernstian response to triethylammonium in the concentration range of 5 x 10(-6)-1 x 10(-2) M with a slope of 58.5 mV per concentration decade in a buffer solution composed of 150 mM NaCl and 10 mM NaH2PO4/Na2HPO4 (pH 7. 5). The limit of detection was 1 muM. In experiments using liposomes, the u ptake of triethylammonium into liposomes was quantitatively induced accordi ng to the pH difference across the liposomal membrane. The transmembrane pH differences in Escherichia coli cells and the light-induced pH differences across the envelope vesicles of Halobacterium halobium were successfully d etermined by the present method.