Spectrophotometric Determination of Micro Amounts of Sulfide, Sulfite and Thiosulfate

The present method is based on the spectrophotometric measurement of an excess amount of iodine for the reaction of iodine with sulfide, sulfite and thiosulfate in a mixture after proper chemical treatments; it consists of three Procedures: I, II and III. The absorbance obtained by Procedure I corresponds to the sum of the thiosulfate and twice the sulfide and sulfite in the mixture. The absorbance obtained by Procedure II, where sulfite was masked by formaldehyde, corresponds to the sum of the thiosulfate and twice the sulfide. The absorbance obtained by Procedure III corresponds to only the amount of thiosulfate, because sulfite was masked by formaldehyde and sulfide was eliminated with the suspension of zinc carbonate hydroxide. The conditions under which all the three sulfur species in a mixture can be stable and react stoichiometrically with iodine were established. The method is applicable to the determination of sulfur species in amounts more than 0.05μmol and gave a relative standard deviation of 3% at 0.4μmol level. It has been applied to the determination of sulfide, sulfite and thiosulfate in various amounts in several fumarolic condensate samples.