LIPOPHILIC IONIC SITES FOR SOLVENT POLYMERIC MEMBRANE PH ELECTRODES BASED ON 4',5'-DIBROMOFLUORESCEIN OCTADECYLESTER AS ELECTRICALLY CHARGED CARRIER

The effect of salt additives on the potentiometric response of solvent polymeric membrane pH electrodes based on the electrically charged ca rrier 4',5'-dibromofluorescein octadecylester (ETH 7075) is evaluated. The incorporation of potassium tetrakis(p-chlorophenyl)borate as anio nic site forces the carrier to reveal its weakly basic properties, onl y showing a Nernstian pH response below pH 2.5 in 0.1 M KCl. In contra st, the presence of tridodecylmethylammonium chloride as cationic site s induces an electrode function that reflects the analytically useful acidic characteristics of the carrier. The latter system shows a pH me asuring range between pH 3.5 and 10 and a selectivity coefficient over potassium of log(HK)(pot)= -8.3. The differences in response behavior are explained qualitatively on the basis of the phase boundary potent ial model.