Construction of liquid membrane type histamine ion-selective electrode

Construction of a liquid membrane type ion-selective electrode sensitive to divalent histaminium cation and its application to potentiometric titration are described. Histamine cation (abbreviated as H2his2+) forms an ion-pair with tetraphenylborate anion (abbreviated as TPB-) in aqueous phase. The extract shows the property of histamine cation-sensitive membrane. Platinized platinum electrode was employed as the internal reference electrode. The calibration curve of the electrode shows a Nernstian response for H2his2+ ion in the concentration range from 10 mM to 15μM. Effect of pH on the electrode potential was observed and the potential is almost constant over the pH range from 1.5 to 6.0. Selectivity coefficients of the histaminium ion-selective electrode was evaluated by means of the separate solution method. Some quaternary ammonium cations showed serious interferences. Sodium tetraphenylborate standard solution was successfully titrated with histamine solution potentiometrically by using the present electrode.