Catalytic hydrogen evolution in the presence of methylthiohydantoin–glycine and cobalt(II) ion: a study by cathodic stripping voltammetry at a hanging mercury drop electrode

Abstract

The carbon–sulfur bond in methylthiohydantoin–glycine (MTH–Gly) is broken during the deposition on the mercury electrode at potentials around −0.1 V versus SCE, giving mercury sulfide which is detected by the characteristic cathodic peak at −0.7 V. If cobalt (II) is also present, the product of the deposition step is a mixture of mercury and cobalt sulfides. During the cathodic scan, the last one is reduced to a transient Co(0) species that catalyses the reduction of hydrogen ion to the hydrogen molecule by a mechanism alike to that emphasized for the Co(II)-sulfide ion system (F.G. Bănică, N. Spătaru, T. Spătaru, Electroanalysis 9 (1997) 1341). This electrode process induces a cathodic peak at −1.4 V that enables the determination of MTH–Gly down to 10 −7 M in the borax buffer at pH 8.5. The possible extension of this method to other classes of organic sulfur compounds is briefly discussed.