engleski

Electrochemical behaviour of methyl 3- mercaptopropionate (3-MPA) at the Hg electrode

Strong interaction between mercury electrode (Hg) and sulfur (S) species serves as a background for their electroanalytical characterization/determination at the Hg electrode. The methodology is based on the tendency of inorganic and organic reduced S species (RSS) to deposit a HgS layer and/or Hg- S species complexes during an accumulation step at the deposition potential around -0.2 V vs. Ag/AgCl. In solutions containing sulfide anions, insoluble HgS layer at the Hg electrode surface is formed by the reversible process of a two-electron oxidation of the Hg at potentials more positive than -0.5 V : HS- + Hg0 → HgS(s) + H+ + 2e- The same process occurs during the interaction of the Hg with some other organic and inorganic S species (thiourea, thiols, oxines, thioanions, polysulfides, dissolved and colloidal S, labile chalcogenides i.e. CuS, PbS, HgS, FeS, Ag2S). During the cathodic potential scan, layers of HgS and adsorbable Hg-S species complexes (in the case of DMS, DMDS, cysteine, glutathione) are reduced between -0.45 and -0.70 V with facilitated reduction of the Hg-S complexes at more positive potential than -0.68 V, where HgS reduction occurs . Methyl 3-mercaptopropionate (3-MPA) is a compound that is frequently discussed in biogeochemical processes in the environment. In addition to cysteine and glutathione, it is one of the most studied organosulfur compounds in natural systems. Its presence in natural waters (depending on whether it is a freshwater or marine system) is mainly explained by the interaction of sulfides and organic matter (acrylates) and/or it can be a product of the biochemical demethylation of dimethylsulfoniopropionate, the main osmolite within the phytoplankton cells. So far, the 3- MPA has been most explored in sediment samples mainly by chromatographic techniques. This paper presents the background of electrochemical behaviour /determination of the 3-MPA (at the Hg electrode) in model electrolyte samples and in the mixture with sulfide. The same principle of determination will be applied for the characterization of S species in selected natural samples. Regarding the electrochemical behaviour of the 3-MPA at the Hg surface, and in comparison, with recorded voltammetric signals in natural samples, the 3-MPA can be a good representative for organosulfur, thiol-like compounds in water environment.

reduced sulfur species ; natural waters ; mercury electrode ; voltammetry ; methyl 3-mercaptopropionate

nije evidentirano