LactatesTo 5 ml of a solution of the substance under examination containing about 5 mg of lactic acid or to 5 ml of the prescribed solution add 1 ml of bromine water and 0.5 ml of 1M sulphuric acid. Heat on a water-bath, stirring occasionally with a glass rod until the colour is discharged. Add 4 g of ammonium sulphate, mix and add dropwise, without mixing, 0.2 ml of a 10 per cent w/v solution of sodium nitroprusside in 1 M sulphuric acid. Without mixing, add 1 ml of strong ammonia solution and allow to stand for 30 minutes; a dark green ring appears at the interface of the two liquids.
Lead CompoundsA. Dissolve 0.1 g of the substance under examination in 1 ml of dilute acetic acid or use 1 ml of the prescribed solution. Add 2 ml of potassium chromate solution; a yellow precipitate insoluble in 2 ml of 10 M sodium hydroxide is produced.
B. Dissolve 50 mg of the substance under examination in 1 ml of dilute acetic acid or use 1 ml of the prescribed solution. Add 10 ml of water and 0.2 ml of 1 M potassium iodide; a yellow precipitate is formed. Heat to boiling for 1 or 2 minutes and allow to cool; the precipitate is reformed as glistening, yellow plates.
Magnesium SaltsA. Dissolve about 15 mg of the substance under examination in 2 ml of water or use 2 ml of the prescribed solution. Add 1ml of dilute ammonia solution; a white precipitate forms that is redissolved by adding 1 ml of 2 M ammonium chloride. Add 1 ml of 0.25 M disodium hydrogen phosphate; a white crystalline precipitate is produced.
B. To 0.5 ml of a neutral or slightly acid solution of the substance under examination add 0.2 ml of a 0.1 per cent w/v solution of titan yellow and 0.5 ml of 0.1 M sodium hydroxide; a bright red turbidity develops which gradually settles to give a bright red precipitate.
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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