Angham Saeed, Ali Modir-Rousta, Christina S. Bottaro

Determination ofsulfur oxyanionsin saline wastewater usingindirect detection, negative-mode capillary zone electrophoresis

Angham Saeed, Ali Modir-Rousta, Christina S. Bottaro

Sulfides and sulfur oxyanions (i.e., thiosalts) are found in the environment and in a number of industrial processes. The presence and transformation of these compounds can impact environmental quality, and can have negative economic consequences. Sulfur-oxygen species can be reduced to the toxic and corrosivehydrogen sulfide in anaerobic environments. Whereas oxidative process on sulfide and sulfur oxyanionscan lead to acidification of the environment and mobilization of toxic metals.The presence of these sulfur compounds can ultimately lead to higher operational costs whether cost of treatment or refit of damaged equipment. It is important to quantify the major charged sulfur species, such as sulfate (SO42-), thiosulfate (S2O32-), tetrathionate (S4O62-), sulfite (SO32-), and sulfide (S2-), to understand the chemistry and behaviour of sulfur-oxygen species as contaminants in process infrastructure.However, analysis ofcharged sulfur species in highly saline water is challenging.The accurate quantitationrequiresbaseline separation and absences co-migration, which is particularly hard to achieve it due to the large peaks associated with sulfate and chloride in saline waters.A capillary zone electrophoresis (CZE)methodhas beendeveloped for the simultaneous detection and quantification of charged sulfur species in highly saline water. The components of the background electrolyte (e.g. pH (buffers), flow modifiers, chromophoric probes, etc.) arethe most important factorsthe development of this method. For example, pyromelliticacid (PMA) is chosen as chromophoric probe because it is non-oxidizing, has high molar absorptivity (high sensitivity), and is a good mobility match for thiosalts, which reduces dispersion. Indirect detection using a chromophoric probe is needed because someof sulfur oxyanionspecieshave little or no absorbance in the UV.This CZE method has been developed for negative mode, i.e. the anions migrate toward the detector, and the electroosmotic flow (EOF) is away from the detector. By adding hexamethonium hydroxide (HMOH) as an EOF modifier toinfluence the chemistry of the capillary surface, shorter time of analysis and better peak resolution were achieved.Other factors that were taken into consideration include:the capillary length, separation temperature, potential applied, and used of a stabilizing agent to limit spontaneous oxidation of some of sulfur-containing compounds.Fast analysis with high separation efficiency and improvementin detection sensitivity were achieved with this method. Optimization efforts and results will be presented.