Evaluating the efficiency of cyclic voltammetry using modified and unmodified glassy carbon electrodes for the analysis of sulfur containing compounds in water
Year: 2017
Type: dissertation
Abstract: When low oxidation state sulfur compounds such as sulfides dissolve in water, they create an undesirable rotten egg smell. A prolonged exposure to concentrations of about 0.01 mg L1- of H2S has been known to have negative effects on human gastro-intestinal, and nervous systems. Concentrations of dissolved low oxidation state sulfur-based compounds in the range of 0.01 to 0.5 mg L1- in aquatic systems have been shown to have chronic and acute toxic effects in aquatic organisms. The ability to qualitatively and quantitatively determine sulfur-based compounds in water, and further be able to speciate these compounds in water would be of great significance. Sulfur-based compounds tend to disproportionate in aqueous solutions to form compounds, the identity of which is dependent on the pH, temperature, and ionic strength of the solution. The work that was investigated in this study involved the detection of simple sulfides (H2S, HS- and S2-) in water through use of cyclic voltammetry (CV), iodometric, and colorimetric techniques. In addition, the analysis of polysulfide and polythionate compounds using these techniques were also investigated in this study. The sodium salts of disulfide (Na2S2), trisulfide (Na2S3), and tetrasulfide (Na2S4) were used in this study as representatives of polysulfides. These compounds were not available commercially and were therefore synthesized. With regards to the CV technique, the bare glassy carbon electrode (BGCE) and the vanadium oxide modified glassy carbon electrode (MGCE) were investigated for their suitability to analyze the polysulfides and thiosulfate. The results obtained in this work demonstrated a potential for use of the CV technique for the qualitative analysis of the above class of compounds. It was however found necessary to first reduce the above type of sulfur compounds to simple sulfide (S2-) before they could successfully be analyzed using the iodometric and colorimetric techniques. Even though the latter two techniques were successfully used for the quantitative analysis of sulfide, the CV technique did not show much success. This was primarily as a result of the unpredictable magnitudes of the various peak currents that resulted. In addition, the background currents especially when the MGCE was used were found to interfere with the peaks associated with sulfide. The colorimetric method and iodometric methods were found to have a great agreement to each other (F (1,10) = 0.418, p = 0.532) for the determination for reduced sulfur-based compounds.
Source: TSpace (University of Toronto)
Author: Ashley Ryan
Language: English
Subfield: Electrochemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2947458274