Testing Procedure (Method of analysis) for Sulphur in Organic Compounds, Tartrates and Thiosulphates

Sulfur in Organic Compounds

A. Bum about 20 mg of the substance under examination by the oxygen-flask method, using 15 ml of water and 2 ml of hydrogen peroxide solution (10 vol) as the absorbing liquid. When combustion is complete, boil the solution gently for 10 minutes, adding water if necessary, and cool. The resulting solution gives the reactions of sulfates.

B. To about 50 mg of the substance under examination add 0.25 g of zinc metal and sodium carbonate reagent, mix and transfer to a small, thin-walled test-tube of hard glass and cover with a layer of the reagent. Carefully heat the tube to red heat, starting at the upper end and heating towards the bottom, and then drop the tube immediately into about 20 ml of water. Filter and acidify the filtrate with hydrochloric acid; fumes which stain lead acetate paper brown or black are evolved.

Tartrates

A. Warm the substance under examination with sulfuric acid; charring occurs and carbon monoxide, which bums with a blue flame when ignited, is evolved.

B. Dissolve about 20 mg of the substance under examination in 5 ml of water or use 5 ml of the prescribed solution. Add 0.05 ml of a 1 percent w/v solution of ferrous sulfate and 0.05 ml of hydrogen peroxide solution (10 vol); a transient yellow color is produced. After the color has disappeared add 2 M sodium hydroxide dropwise; an intense blue color is produced.

C. Heat 0.1 ml of solution containing about 2 mg of tartaric acid or 0.1 ml of prescribed solution on a water-bath for 5 to 10 minutes with 0.1 ml of a 10 percent w/v solution of potassium bromide, 0.1 ml of 2 percent w/v solution of resorcinol and 3 ml of sulfuric acid; a dark blue color that changes to red when the solution is cooled and poured into water is produced.

Thiosulphates

A. Dissolve 0.1 g of the substance under examination in 5 ml of water and add 2 ml of hydrochloric acid; a white precipitate is formed which soon turns yellow and sulfur dioxide, recognizable by its odor, is evolved.

B. Dissolve 0.1 g of the substance under examination in 5 ml of water and add 2 ml of ferric chloride test solution; a dark violet color which quickly disappears is produced.

C. Solutions of thiosulphates decolorize iodine solution; the decolorized solutions do not give the reactions of sulfates.

D. Solutions of thiosulphates decolorize bromine solution; the decolorized solutions give the reactions of sulfates.

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