engleski

Application of the electroanalytical methods for characterization of reduced sulfur species (HS-, S0, SX2-, RSH, S4O62-) in natural waters

Electroanalytical methods (EM) at the mercury (Hg) electrode are widely used for the determination of different reduced sulfur species (RSS: HS- , S0 , SX 2- , RSH, S4O6 2- ) in natural waters due to the strong interaction between RSS and the Hg [1, 2]. The application of EM allows the direct determination of RSS without prior processing of the natural samples, but the determination of individual RSSin mixture samples remains a challenge due to low RSS concentrations, thermodynamic unstabilities and changes in RSS speciation during sampling and sample manipulation, as well as due to different analytical windows of the used EM. In this paper voltammetric methods: cyclic (CV), differential pulse (DPV), and sampled direct current voltammetry (SDC) were used to measure individual RSS and mixture solutions, while the euxinic water column of the marine Rogoznica Lake (RL) [1, 2] was chosen as the natural study site for application and testing of the EM. CV in the solutions of HS- , S0 and SX 2- revealed a similar HgS reduction peak around - 0.68 V (vs. Ag/Ag/Cl). In the case of tetrathionate and glutathione, more positive peaks (corresponding to their Hg complexation) than HgS reduction are revealed. In mixtures of these RSS, the HgS formation and its reduction at about -0.70 V is the most pronounced, and only the HgS reduction is obtained. This peak is usually taken as a measure of the total RSS in the studied samples. DPV was used for direct determination of SX 2- and recorded well-defined current minimums around -1.0 V demonstrated the presence of SX 2- , which in the euxinic RL samples were measured up to 153 µM of polysulfidic S0 . SDC measured total S0 including soluble (S8-aq), polysulfidic and colloidal S0 . Obtained results indicate that each of the used EM has its own detection window which can measure different S0 forms that produce different EM responses. DLS measurements additionally proved changes in S0 colloidal solution visible by recording different hydrodynamic properties (radius) of S0 upon different dilutions of the original sample. The same effect is observed in the RL euxinic samples. In such experimental conditions, it appears that RSS becomes more electrochemically active, or they are simply more easily delivered (as being faster in smaller forms) to the Hg, giving the higher current of the HgS reduction. ACKNOWLEDGMENTS This work was funded by Croatian Science Foundation, IP-2018-01-1717- MARRES REFERENCES [1] I. Ciglenečki, M. Marguš, E. Bura – Nakić, I. Milanović, J. Electrochem. Sci. Eng. 2 (2014) 155-163. [2] E. Bura-Nakić, G.R. Helz, I. Ciglenečki, B. Ćosović, Geochim Cosmochim Acta 73 (2009) 3738–3751.

electroanalytical methods ; Reduced sulfur species ; dynamic light scattering

nije evidentirano