ChloridesA. Dissolve a quantity of the substance under examination equivalent to about 2 mg of chloride ion in 2 ml of water or use 2 ml of the prescribed solution. Acidify with dilute nitric acid, add 0.5 ml of silver nitrate solution, shake and allow to stand; a curdy white precipitate is formed, which is insoluble in nitric acid but soluble, after being well washed with water, in dilute ammonia solution, from which it is reprecipitated by the addition of dilute nitric acid.
B. Introduced into a test-tube a quantity of the substance under examination equivalent to about 10 mg of chloride ion, add 0.2 g of potassium dichromate and 1 ml of sulphuric acid. Place a filter-paper strip moistened with 0.1 ml of diphenylcarbazide solution over the mouth of the test-tube; the paper turns violet-red. (Do not bring the moistened paper into contact with the potassium dichromate solution).
CitratesA. To a neutral solution of the substance under examination add a solution of calcium chloride; no precipitate is produced. Boil the solution; a white precipitate soluble in 6 M acetic acid is produced.
B. Dissolve a quantity of the substance under examination containing about 50 mg of citric acid in 5 ml of water or use 5 ml of the prescribed solution. Add 0.5 ml of sulphuric acid and 3 ml of potassium permanganate solution. Warm until the colour of the permanganate is discharged and add 0.5 ml of a 10 per cent w/v solution of sodium nitroprusside in 1 M sulphuric acid and 4 g of sulphamic acid. Make alkaline with strong ammonia solution, added dropwise until all the sulphamic acid has dissolved. On addition of an excess of strong ammonia solution, a violet colour, which turns violet blue, is produced.
EstersTo about 30 mg. of the substance under examination or to the prescribed quantity add 0.5 ml of a 7 per cent w/v solution of hydroxylamine hydrochloride in methanol and 0.5 ml of a 10 per cent w/v solution of potassium hydroxide in ethanol (95 per cent). Heat to boiling, cool, acidify with 2 M hydrochloric acid and add 0.2 ml of a 1 per cent w/v solution of ferric chloride; a bluish-red or red colour is produced.
Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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