Comparing different approaches for assembling selective electrodes for heavy metals

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.