monograph of strong ammonium solution

General Notices
(Ph Eur monograph 0877)
Preparation
Dilute Ammonia Solution
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DEFINITION
Concentrated ammonia solution contains not less than 25.0 per cent m/m and not more than 30.0 per cent m/m of ammonia (NH3; M r 17.03).
CHARACTERS
A clear , colourless liquid, very caustic, miscible with water and with alcohol.
IDENTIFICATION
A. Relative density (2.2.5): 0.892 to 0.910.
B. It is strongly alkaline (2.2.4) .
C. To 0.5 ml add 5 ml of water R. Bubble air through the solution and lead the gaseous mixture obtained over the surface of a solution containing 1 ml of 0.1 M hydrochloric acid and 0.05 ml of methyl red solution R. The colour changes from red to yellow. Add 1 ml of sodium cobaltinitrite solution R. A yellow precipitate is formed.
TESTS
Solution S
Evaporate 220 ml almost to dryness on a water-bath. Cool, add 1 ml of dilute acetic R and dilute to 20 ml with distilled water R.
Appearance of solution
To 2 ml add 8 ml of water R. The solution is clear (2.2.1) and colourless (2.2.2, Method II).
Oxidisable substances
Cautiously add, whilst cooling, 8.8 ml to 100 ml of dilute sulphuric acid R. Add 0.75 ml of 0.002 M potassium permanganate . Allow to stand for 5 min. The solution remains faintly pink.
Pyridine and related substances
Measure the absorbance (2.2.25) at 252 nm using water R as the compensation liquid. The absorbance is not greater than 0.06 (2 ppm calculated as pyridine).
Carbonates
To 10 ml in a test-tube with a ground-glass neck add 10 ml of calcium hydroxide solution R. Stopper immediately and mix. Any opalescence in the solution is not more intense than that in a standard prepared at the same time and in the same manner using 10 ml of a 0.1 g/l solution of anhydrous sodium carbonate R (60 ppm).
Chlorides (2.4.4)
Dilute 5 ml of solution S to 15 ml with water R. The solution complies with the limit test for chlorides (1 ppm).
Sulphates (2.4.13)
Dilute 3 ml of solution S to 15 ml with distilled water R. The solution complies with the limit test for sulphates (5 ppm).
Iron (2.4.9)
Dilute 4 ml of solution S to 10 ml with water R. The solution complies with the limit test for iron (0.25 ppm).
Heavy metals (2.4.8)
Dilute 4 ml of solution S to 20 ml with water R. 12 ml of the solution complies with limit test A for heavy metals (1 ppm). Prepare the standard using lead standard solution (2 ppm Pb) R.
Residue on evaporation
Evaporate 50 ml to dryness on a water-bath and dry at 100°C to 105°C for 1 h. The residue weighs not more than 1 mg (0.02 g/l).
ASSAY
Weigh accurately a flask with a ground-glass neck containing 50.0 ml of 1 M hydrochloric acid . Add 2 ml of the substance to be examined and re-weigh. Add 0.1 ml of methyl red solution R as indicator. Titrate with 1 M sodium hydroxide until the colour changes from red to yellow.
1 ml of 1 M hydrochloric acid is equivalent to 17.03 mg of NH3.
STORAGE
Store protected from air, at a temperature not exceeding 20°C.
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