K. Hiratani, T. Takahashi, H. Sugihara, K. Kasuga, K. Fujiwara,
T. Hayashita, and R. A. Bartsch
[Anal. Chem., Vo.69, pp.3002-3007, 1997]

The effects of the chain structure and substituents in six acyclic polyether dicarboxylic acids and one acyclic polyether carboxylic acid upon the efficiency and selectivity of pH-driven Pb²⁺ transport in a bulk chloroform membrane system have been assessed. Among the carriers, 1,2-bis[2-(o-carboxyphenoxy) ethoxy]-4-tert-butylbenzene (1) is found to exhibit high selectivity for transport of Pb²⁺ compared with alkali metal cations and a variety of other divalent metal ion species. Ionophore 1 also extracts Pb²⁺ from aqueous solution into chloroform with the loss of two protons. A 1:1 complex of Pb²⁺ with di-ionized 1 has been isolated.