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 1.0×10 −5 –1.0×10 −1 M and the slope was 54.7±0.5 mV/dec. The detection limit was determined to be 9.0×10 −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 NH 4 + , −4.5 for Mg 2+ , −5.0 for Ca 2+ ,−4.9 for Ba 2+ . The lifetime of the membrane was about one month.