Polarographic determination of dithionite and its decomposition products: kinetic aspects, stabilizers, and analytical application Original Research Article

Differential pulse polarography (DPP) was employed to show the mechanism and the kinetic of dithionite decomposition in aqueous solution. Using different supporting electrolyte solutions the determination of dithionite, thiosulfate, sulfide and elemental sulfur without interferences was shown to be possible. A systematic and comparative study of the dithionite stability was carried out using different stabilizing mediums described in the literature. The most effective stabilizer was found to be formaldehyde. After the reaction with formaldehyde in aqueous solution, dithionite can be polarographic determined, based on its electrochemical activity as hydroxymethanesulfinate ion. The procedures were applied for the determination of dithionite as well as its decomposition products, thiosulfate and sulfide, in commercial formulations of decolorants used in the household. In a 0.1 g sample of decolorant, dithionite was found to be the major component in concentrations between 27 and 35% (w/w). Thiosulfate and sulfide was also found to be present in the samples as decomposition products (0.25–0.47 and 0.06–0.07% (w/w), respectively), which can be determined without interference of dithionite and additives present in the formulations.