Transformation of polysulfidic sulfur to elemental sulfur in a chelated iron, hydrogen sulfide oxidation process

Polysulfides, S2−x, formed in the oxidative absorption of hydrogen sulfide, are labile, linear polyatomic compounds and readily decompose to elemental sulfur in aqueous solutions. The initial identification of polysulfide species that are found in solutions containing chelated Fe(III) and H2S using laser desorption Fourier transform ion cyclotron resonance (LD-FTICR) mass spectrometry is described. LD is shown to be a superior ionization method because rearrangement and/or fragmentation product ions that are often observed in electron-impact and chemical-ionization methods are absent in LD mass spectra. The LD-FTICR studies indicate that trisulfide is the dominant polysulfide species in aqueous solution under the experimental conditions employed ([Fe] = 0.018 M and [L] = 0.036 M at pH 8.5, where L = nitrilotriacetic acid), and disulfide, tetrasulfide and pentasulfide are present in lesser proportions.