Caffeine: About 0.3 g of the substance (exact weight) is dissolved in 30 ml of water in a 100 ml volumetric flask. To the solution add 10 ml of diluted sulfuric acid, 50 ml of 0.1 mol / l solution of iodine, the volume of the solution is brought to the mark with water and stirred. After settling for 15 minutes, the solution is quickly filtered through a layer of cotton into a dry flask, covering the funnel with a watch glass. The first 10-15 ml of filtrate is discarded. Transfer 50 ml of the filtrate to the flask and excess iodine titrate with 0.1 mol / l sodium thiosulfate solution until bleaching (indicator – starch). Concurrently conduct a control experiment.
1 ml of 0.1 mol / l solution of iodine corresponds to 0.004855 g of caffeine, which, in terms of dry substance, should be not less than 38%, 0% and not more than 40.0%
Sodium benzoate: About 0.15 g of the substance (exact mass) is dissolved in 10 ml of water in a flask with a ground stopper with a capacity of 50 ml, 10 ml of ether are added, 2-3 drops of a mixed indicator (2 drops of a solution of methyl orange and 1 drop of a solution of methylene blue) and titrated 0.1 mol / l solution of hydrochloric acid until the lilac color of the aqueous layer. At the end of the titration, the contents of the flask are well shaken.
When methyl orange is used as an indicator, the titration is carried out before the pink color of the aqueous layer.
1 ml of 0.1 M solution of hydrochloric acid corresponds to 0.014441 g of sodium benzoate, which, in terms of dry substance, should be not less than 58.0% and not more than 62.0%
Theophylline Substance Analysis
Description. The white crystalline powder is odorless.
Solubility. Slightly soluble in water and 95% alcohol, ether and chloroform, easily soluble in hot water and hot 95% alcohol, soluble in acids and alkali solutions.
Authenticity. 0.05 g of the substance is placed in a porcelain dish, 10 drops of diluted hydrochloric acid are added, 10 drops of perhydrol and evaporated to dryness in a water bath. The residue is moistened with 1-2 drops of ammonia solution; a purple-red coloration appears.
To 0.5 g of the drug is added 2 ml of 0.1 mol / l sodium hydroxide solution, shaken for 2 minutes and filtered. To the filtrate add 3 drops of a 2% solution of cobalt chloride and mix; a white precipitate is formed with a pinkish tinge (unlike theobromine and caffeine).
Acidity and alkalinity. 0.5 g of the substance is dissolved in 75 ml of freshly boiled water and 1 drop of methyl red solution is added; the appeared red color should turn into yellow from the addition of no more than 0.4 ml of 0.05 mol / l sodium hydroxide solution.
Other purine bases. A solution of 0.2 g of the substance in 5 ml of ammonia should be clear and colorless.
Organic impurities. A solution of 0.1 g of the substance in 2 ml of concentrated sulfuric acid should be clear and colorless.
Loss on drying. About 0.5 g of the substance (exact weight) is dried at 100-105 0 С to a constant weight. Loss in weight during drying should not exceed 9.5%.
Quantitation. About 0.4 g (weighed weight) of the pre-dried substance is dissolved in 100 ml of boiling water (pre-boiled for 5 minutes). 25 ml of a 0.1 mol / l solution of silver nitrate, 1-1.5 ml of a solution of phenol red are added to the cooled solution and titrated with a 0.1 mol / l solution of sodium hydroxide until a violet-red color appears.
1 ml of 0.1 mol / l solution of caustic soda corresponds to 0.01802 g of theophylline, which, in terms of dry substance, must be at least 99%
Analysis of the substance of aminophylline
Description. White or white with a yellowish sheen crystalline powder with a faint ammonia smell. On the air absorbs carbon dioxide, while the solubility decreases.
Solubility. Soluble in water. Aqueous solutions of the drug are alkaline.
Authenticity. 0.1 g of the substance is dissolved in 4 ml of water. 1 ml of this solution is placed in a porcelain dish, 5 drops of diluted hydrochloric acid are added, 10 drops of perhydrol and evaporated to dryness in a water bath. When the residue is wetted with 1-2 drops of an ammonia solution, a purple-red color appears.
To 3 ml of the same solution add 5 drops of copper sulphate solution; there is a bright purple color.