Ionophores in rubidium ion-selective membrane electrodes

Binaphthyl-based crown ethers incorporating anthraquinone, benzoquinone, and 1,4-dimethoxybezene have been synthesized and tested for Rb+ selective ionophores in the poly(vinyl chloride) (PVC) membrane. The membrane containing NPOE gave a better Rb+ selectivity than those containing either DOA or BPPA as a plasticizer. The response was linear within the concentration range of 1.0 x 10(-5) - 1.0 x 10(-1) M and the slope was 54.7 +/- 0.5 mV/dec. The detection limit was determined to be 9.0 x 10(-6) M and the optimum pH range of the membrane was 6.0 - 9.0. The ISE membrane exhibits good selectivity for Rb+ over ammonium, alkali metal, and alkaline earth metal ions. Selectivity coefficients for the other metal ions, log K-Pot were - 2.5 for Li+, - 2.4 for Na+, - 2.0 for H+, - 1.0 for K+, - 1.2 for Cs+, - 1.6 for NH4+, - 4.5 for Mg2+ - 5.0 for Ca2+, - 4.9 for Ba2+. The lifetime of the membrane was about one month.