Comparing Different Approaches for Assembling Selective Electrodes for Heavy Metals

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Different approaches for increasing the sensitivity and selectivity of voltammetric probes for heavy metals have been examined. These have involved adsorbed monolayers of host molecules, functionalized self-assembled monolayers and thin polymeric films. Two systems are presented that focus on the selective analysis of Hg(II) and Fe(II). The electrode for Hg(II) is based on a macrocyclic ligand, i.e., Kryptofix-222, while that for Fe(II) relies on the selective complexation by ferroin ligands, such as 1,10-phenanthroline. The monomeric and polymeric approaches were examined and compared for both systems. The principal aim of this manuscript is to highlight the ability of fine-tuning the selectivity characteristics of the solid-liquid interface as a result of considering and optimizing analyte-interface interactions. We find that basically, an interface comprising a monolayer, which is capable of forming a strong and selective complex with the analyte, is likely to exhibit sensitivity that is at least as good as a polymeric film. On the other hand, the stability and durability of the latter usually makes it a superior interface for repetitive analysis and will therefore be the preferred choice for flow analysis systems.