Homocysteine and its thiolactone: behavior in cathodic stripping voltammetry at a mercury electrode

Homocysteine (Hcy) forms a sparingly soluble mercury thiolate under anodic polarization at a mercury electrode and mercury ion reduction in this compound gives rise to a characteristic cathodic stripping peak (A). If the nickel ion is present, Hcy released by this reaction does catalyze nickel ion reduction and yields a second cathodic peak (B) at about –0.75 V. Nickel ion has no effect on the peak A. Homocysteine-thiolactone (HTL) is electrochemically inactive under similar conditions, but Hcy impurity that is present in the commercial MTH reagent develops both peaks A and B under suitable conditions. Hcy impurity in HTL can therefore be assessed by cathodic stripping voltammetry.