Potential changes during in situ formation of carriers for cationic surfactant ion-selective electrodes by conditioning

The potential changes were monitored during symmetric conditioning and asymmetric conditioning of the polyvinyl chloride membrane containing sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB) or sodium tetraphenylborate (NaTPB) in dodecyltrimethylammonium chloride (DTMACl) solutions at 10−5.0-10−3.5 mol dm−3. A slow potential increase, which reflected a change in local concentration of DTMA+ in the conditioning solution proximate to the membrane, was observed for NaTFPB at a DTMACl concentration of 10−5.0-10−4.5 mol dm−3. For NaTFPB at a DTMACl concentration of 10−4.0-10−3.5 mol dm−3 or for NaTPB, the potential decreased after a rapid increase reflecting the change in DTMA+:Na+ ratio as a counter ion in the membrane by the ion-exchange. In asymmetric conditioning, the leakage of DTMA+ into the inner solution overlapped with the change in DTMA+:Na+ ratio for NaTPB but was delayed from the change for NaTFPB. Some criteria for completion of the conditioning are described.