Lead-selective poly(vinyl chloride) membrane electrodes based on acyclic dibenzopolyether diamides

Lipophilic acyclic dibenzopolyether diamides, 12 kinds, have been designed to prepare solvent polymeric membrane ion-selective electrodes (ISEs) for Pb⁺². The ionophores include 1,5-bis[2-(N,N-dialkylcarbamoylmethoxy)phenoxy]-3-oxapentanes 1-4, 1,5-bis[2-(N,N-dialkylcarbamoylpentadecyloxy)phenoxy]-3-oxapentanes 5-8, and 1,2-bis[2-(2'-N,N-dialkylcarbamoylpentadecyloxy)phenoxy]ethanes 9 12. Linear response concentration range of the ISE based on 9 is 3 x 10^-2 - 1 x 10^-6 M of Pb²⁺ (average slope = 28.5 mV decade^-1). Potentiometric selectivities of the ISEs based on 1-12 for Pb²⁺ over other heavy metal cations, alkali metal cations, and alkaline earth metal cations have been assessed. These ISEs exhibit remarkably high selectivities for Pb²⁺ relative to heavy metal cations, such as Cu²⁺, Fe²⁺, and Ni²⁺, the selectivity coefficients (K(Pb.Cu)/(Pot)) being 5 x 10^-5 - 6 x 10^-5 - for 1-4 and ca. 6 x 10^-4 - for 9. For the Pb²⁺ selectivities over alkali metal cations, such as Na⁺ and K⁺, 9 which has an ethylene glycol spacer and a N,N-diethyl group is superior to other dibenzopolyether diamide ionophores 1-8 and 10-12.