Sodium and Sodium Salts

 A. Dissolve 0.1 g of the substance to be examined in 2 ml of water R or use 2 ml of the prescribed solution. Add 2 ml of a 150 g/l solution of potassium carbonate R and heat to boiling. No precipitate is formed. Add 4 ml of potassium pyroantimonate solution R and heat to boiling. Allow to cool in iced water and if necessary rub the inside of the test-tube with a glass rod. A dense white precipitate is formed.

 B. Dissolve a quantity of the substance to be examined equivalent to about 2 mg of sodium (Na⁺) in 0.5 ml of water R or use 0.5 ml of the prescribed solution. Add 1.5 ml of methoxyphenylacetic reagent R and cool in ice-water for 30 min. A voluminous, white, crystalline precipitate is formed. Place in water at 20 °C and stir for 5 min. The precipitate does not disappear. Add 1 ml of dilute ammonia R1. The precipitate dissolves completely. Add 1 ml of ammonium carbonate solution R. No precipitate is formed.

Sulphates

 A. Dissolve about 45 mg of the substance to be examined in 5 ml of water R or use 5 ml of the prescribed solution. Add 1 ml of dilute hydrochloric acid R and 1 ml of barium chloride solution R1. A white precipitate is formed.

 B. To the suspension obtained during reaction (a), add 0.1 ml of 0.05 M iodine. The suspension remains yellow (distinction from sulphites and dithionites), but is decolorised by adding dropwise stannous chloride solution R (distinction from iodates). Boil the mixture. No coloured precipitate is formed (distinction from selenates and tungstates).

Tartrates

 A. Dissolve about 15 mg of the substance to be examined in 5 ml of water R or use 5 ml of the prescribed solution. Add 0.05 ml of a 10 g/l solution of ferrous sulphate R and 0.05 ml of dilute hydrogen peroxide solution R. A transient yellow colour is produced. After the colour has disappeared add dilute sodium hydroxide solution R dropwise. A violet or purple colour is produced.

 B. To 0.1 ml of a solution of the substance to be examined containing the equivalent of about 15 mg of tartaric acid per millilitre or to 0.1 ml of the prescribed solution add 0.1 ml of a 100 g/l solution of potassium bromide R, 0.1 ml of a 20 g/l solution of resorcinol R and 3 ml of sulphuric acid R. Heat on a water-bath for 5 min to 10 min. A dark-blue colour develops. Allow to cool and pour the solution into water R. The colour changes to red.

Xanthines

To a few milligrams of the substance to be examined or the prescribed quantity add 0.1 ml of strong hydrogen peroxide solution R and 0.3 ml of dilute hydrochloric acid R. Heat to dryness on a water-bath until a yellowish-red residue is obtained. Add 0.1 ml of dilute ammonia R2. The colour of the residue changes to violet-red.

Zinc and Zinc Salts

Dissolve 0.1 g of the substance to be examined in 5 ml of water R or use 5 ml of the prescribed solution. Add 0.2 ml of strong sodium hydroxide solution R. A white precipitate is formed. Add a further 2 ml of strong sodium hydroxide solution R. The precipitate dissolves. Add 10 ml of ammonium chloride solution R. The solution remains clear. Add 0.1 ml of sodium sulphide solution R. A flocculent white precipitate is formed.

Date: 2015-12-24; view: 967