Method for the Determination of Inorganic Polysulfide Distribution in Aquatic Systems

Abstract

Inorganic polysulfides have significant technological importance, and their environmental role is gradually being unraveled. But despite their importance, there is still no method for quantification of the individual members of the polysulfide family in nonsynthetic samples. The method is based on fast, single-phase derivatization with methyl trifluoromethanesulfonate followed by one of three modes of sample treatment depending on polysulfide concentration. Under the most aggressive preconcentration treatment involving liquid-liquid extraction, solvent evaporation to dryness, dissolution in n-dodecane, and finally HPLC-UV analysis of the dimethylpolysulfane distribution, the minimum detection limits of the individual polysulfides are in the range 15-70 nM. The method was demonstrated for the analysis of synthetic solutions, natural groundwater, polysulfide fortified seawater, and surface water and for time tracing of the distribution of the individual polysulfides during the oxidation of hydrogen sulfide by hydrogen peroxide. The observed speciation was evaluated by comparison with the theoretical distribution of polysulfides at equilibrium with sulfur precipitate showing that the dominant polysulfides' (i.e., tetra- to hexasulfide) concentrations agree well with the predicted distribution (90% of the results fall within less than 30% deviation from the predicted values), whereas up to 3-fold deviation was observed for the less abundant trisulfide and octasulfide species.