Screening highly selective ionophores for heavy metal ion-selective electrodes and potentiometric sensors

Abstract

Screening highly selective ionophores from a large amount of ionophores is the principle and most realizable method to discover new ionophores used in ion-selective electrodes (ISEs). In this paper a screening method is described for ionophore-based polymeric membrane heavy metal ion-selective electrodes (IBPMHM ISEs) to determine heavy metal ions (Cu2+, Pb2+, Zn2+, Cd2+, Hg2+ and Ag+). The protocol uses the averaged negative logarithmic potential selectivity coefficients (pK5¯) of five major interfering ions as screening parameters. The specified five major interfering ion group (Group A) can enhance the screening ability of the parameter pK5¯. The molecular categories of preferred ionophores (pK5¯>2.00) for these ISEs were as follows: Schiff bases for Cu2+-ISE; Schiff bases and macrocycles for Zn2+-ISE; calixarenes, crown ethers and macrocycles for Ag+-ISE; calixarenes, Schiff bases and crown ethers for Pb2+-ISE, and another group for both Cd2+- and Hg2+-ISEs. Strong interaction between the donor atoms of ionophores and the heavy metal ions follows the hard soft acids and bases rule (HSAB). This approach efficiently screens the best ionophores for these IBPMHM ISEs, and provides a new route to explore new ionophores for other ionophore-based ISEs and potentiometric sensors.