Electrochemical metal speciation using self-assembled monolayers

The application of self-assembled monolayers (SAMs) as a means of achieving speciation in heavy metal electrochemical determination is demonstrated. SAMs are monomolecular organic layers that can be chemically attached onto different electrode materials and used for the selective extraction of heavy metals. The selectivity is achieved by assembling monolayers that have pendant ligands, which interact selectively with the analytes in the solution. For example, the formation of a monolayer comprising a pyridine group was used to selectively extract Cr(VI) from aqueous solutions, whereas the selective determination of Fe(II) was accomplished using a covalently bound terpyridine monolayer. Yet, determining the heterogeneous binding constants of the metallic species by the SAMs is of significant importance and allows studying quantitatively the interactions between the monolayer and the metal ions. We have developed a few methods for determining the binding constants of heavy metal ions by SAMs of which two of them are briefly discussed here.