Homocysteine Voltammetry at a Mercury Electrode in the Presence of Nickel

At a mercury electrode, Hcy and Cys yield similar cathodic stripping peaks connected to the reduction ()I the pertinent mercury thiolate However, due the different behavior as a ligand for nickel ion, the above compounds perform very differently in the presence of this ion Whereas the nickel ion at a high enough concentration suppresses the Cys peak. in the case of Hcy it causes the cathodic peak to shift to more negative potentials The peculiar behavior of Hcy is due to the stabilization of the mercury thiolate surface layer by intermolecular Ni2+ bridges within the surface layer Conversely. in the case of Cys. the nickel ion strongly competes with the mercury ion and leads to the formation of a surface adsorbed bis-cystematonickelate complex. which prevents the formation of mercury cystemate Such a difference allows determining licy by cathodic snipping voltammetry in the presence of nickel ion with no Cys interference