BARIUM ION-SELECTIVE ELECTRODE BASED ON A NEW NEUTRAL CARRIER COMPLEX

Three derivatives of a new class of ionophores belonging to the binaphthyl polyethers and exhibiting high lipophilicity were synthesized and evaluated as neutral carriers for the fabrication of a barium ion-selective electrode. The influence of the length of the ether side-chain and of the substitution of the amido group ending this side-chain on the complexing capability of barium ion is discussed. The ion-selective membrane was constructed by incorporating the selected ionophore in an ethylene-vinyl acetate copolymer which was previously dissolved in tetrahydrofuran. Nitrophenyl octyl ether was used as a plasticizer and a small amount of sodium tetraphenylborate was added as a lipophilic anion. The influence of the nature of the plasticizer and of the amount of incorporated ionophore on the characteristics of the electrode is discussed. The response of this electrode is linear in the range 0.1-3 x 10(-6) M with a slope of 30 mV per decade. The potential is not affected by pH modifications in the range 1.6-8.1. Selectivity coefficients determined for both monovalent and divalent cations show negligible interference from most of them. The electrode exhibits excellent potential stability and an operational lifetime of more than 5 months. Moreover, this electrode is not poisoned by copper(II) ions, in contrast with an ion-exchanger liquid membrane electrode, which exhibits a potential shift, or with a PVC membrane electrode, which requires in this instance a long recovery time. This electrode was applied successfully to the determination of sulphate ions in commercial mineral waters using potentiometric titration.