Testing Procedure (Method of analysis) for Mercury Compounds, Nitrates and Phosphates (Orthophosphates) : Pharmaceutical Guidelines

Testing Procedure (Method of analysis) for Mercury Compounds, Nitrates and Phosphates (Orthophosphates)

Learn the testing procedure of Mercury Compounds, Nitrates and Phosphates (Orthophosphates) in Pharmaceutical substances.

Mercury Compounds

A. Place 0.05 to 0.1 ml of a solution of the substance under examination on a well-scraped copper foil; a dark grey stain, which becomes shiny on rubbing, is produced. Heat the dried copper foil in a test-tube; the spot disappears.
B. To a solution of the substance under examination add carefully potassium iodide solution; a red precipitate is produced which is soluble in an excess of the reagent (mercuric compounds) or a yellow precipitate is produced which may become green on standing (mercurous compounds).
C. To the prescribed solution add 2 M sodium hydroxide until strongly alkaline; a dense, yellow precipitate is produced (mercuric compounds).
D. To a solution of the substance under examination add 6 M hydrochloric acid; a white precipitate is produced which is blackened by adding dilute ammonia solution (mercurous compounds).


A. Dissolve 15 mg of the substance under examination in 0.5 ml of water, add cautiously 1 ml of sulphuric acid, mix and cool. Incline the tube and carefully add, without mixing, 0.5 ml of ferrous sulphate solution; a brown colour is produced at the interface of the two liquids.
B. To a mixture of 0.1 m1 of nitrobenzene and 0.2 ml of sulphuric acid add a quantity of the powdered substance under examination equivalent to about 1 mg of nitrate ion or the prescribed quantity. Allow to stand for 5 minutes and cool in ice whilst adding slowly with stirring 5 ml of water and then 5 ml of sodium hydroxide solution. Add 5 ml of acetone, shake and allow to stand; the upper layer shows an intense violet colour.

Phosphates (Orthophosphates)

A. To 5 ml of the prescribed solution, neutralised to pH 7.0, add 5 ml of silver nitrate solution; a light yellow precipitate forms, the colour of which is not changed by boiling and which is readily soluble in 10M ammonia and in dilute nitric acid.
B. Mix 1 ml of the prescribed solution with 1 ml of ammoniacal magnesium sulphate solution; a white crystalline precipitate is formed.
C. To 2 ml of the prescribed solution and 2 ml of dilute nitric acid and 4 ml of ammonium molybdate solution and warm the solution; a bright yellow precipitate is formed.

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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