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

Differential pulse polarography (DPP) was employed to show the mechanism an d the kinetic of dithionite decomposition in aqueous solution. Using differ ent supporting electrolyte solutions the determination of dithionite, thios ulfate, sulfide and elemental sulfur without interferences was shown to be possible. A systematic and comparative study of the dithionite stability wa s carried out using different stabilizing mediums described in the literatu re. The most effective stabilizer was found to be formaldehyde. After the r eaction with formaldehyde in aqueous solution, dithionite can be polarograp hic determined, based on its electrochemical activity as hydroxymethanesulf inate ion. The procedures were applied for the determination of dithionite as well as its decomposition products, thiosulfate and sulfide, in commerci al formulations of decolorants used in the household. In a 0.1 g sample of decolorant, dithionite was found to be the major component in concentration s between 27 and 35% (w/w). Thiosulfate and sulfide was also found to be pr esent 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 dithion ite and additives present in the formulations. (C) 2001 Elsevier Science B. V. All rights reserved.