Ammonium Ichthosulphonate
(Ph. Eur. monograph 0917)
Action and use
Chronic lichenified eczema.
Preparation
Zinc and Ichthammol Cream
DEFINITION
Ichthammol is obtained by distillation from certain bituminous schists, sulfonation of the distillate and neutralisation of the product with ammonia.
Content
— dry matter: 50.0 per cent m/m to 56.0 per cent m/m;
— total ammonia (NH3; Mr 17.03): 4.5 per cent m/m to 7.0 per cent m/m (dried substance);
— organically combined sulfur: minimum 10.5 per cent m/m (dried substance);
— sulfur in the form of sulfate: maximum 20.0 per cent m/m of the total sulfur.
CHARACTERS
Appearance
Dense, blackish-brown liquid.
Solubility
Miscible with water and with glycerol, slightly soluble in ethanol (96 per cent), in fatty oils and in liquid paraffin. It forms homogeneous mixtures with wool fat and soft paraffin.
IDENTIFICATION
A. Dissolve 1.5 g in 15 mL of water R (solution A). To 2 mL of solution A add 2 mL of hydrochloric acid R. A resinous precipitate is formed. Decant the supernatant. The precipitate is partly soluble in ether R.
B. 2 mL of solution A, obtained in identification test A, gives the reaction of ammonium salts and salts of volatile bases (2.3.1).
C. Evaporate and ignite the mixture of solution A and dilute sodium hydroxide solution R obtained in identification test B. Take up the residue with 5 mL of dilute hydrochloric acid R. Gas is evolved which turns lead acetate paper R brown or black. Filter the solution. The filtrate gives reaction (a) of sulfates (2.3.1).
TESTS
Acidity or alkalinity
To 10.0 mL of the clear filtrate obtained in the assay of total ammonia add 0.05 mL of methyl red solution R. Not more than 0.2 mL of 0.02 M hydrochloric acid or 0.02 M sodium hydroxide is required to change the colour of the indicator.
Relative density (2.2.5)
1.040 to 1.085, determined on a mixture of equal volumes of the substance to be examined and water R.
Sulfated ash (2.4.14)
Maximum 0.3 per cent, determined on 1.00 g.
ASSAY
Dry matter
Weigh 1.000 g in a tared flask containing 2 g of sand R, previously dried to constant mass, and a small glass rod. Heat on a water-bath for 2 h with frequent stirring and dry in an oven at 100-105 °C until 2 consecutive weighings do not differ by more than 2.0 mg; the 2 weighing is carried out after drying again for 1 h.
Total ammonia
Dissolve 2.50 g in 25 mL of warm water R. Rinse the solution into a 250 mL volumetric flask, add 200 mL of sodium chloride solution R and dilute to 250.0 mL with water R. Filter the solution, discarding the first 20 mL of filtrate. To 100.0 mL of the clear filtrate add 25 mL of formaldehyde solution R, neutralised to phenolphthalein solution R1. Titrate with 0.1 M sodium hydroxide until a faint pink colour is obtained.
1 mL of 0.1 M sodium hydroxide is equivalent to 1.703 mg of NH3.
Organically combined sulfur
Mix 0.500 g with 4 g of anhydrous sodium carbonate R and 3 mL of methylene chloride R in a porcelain crucible of about 50 mL capacity, warm and stir until all the methylene chloride has evaporated. Add 10 g of coarsely powdered copper nitrate R, mix thoroughly and heat the mixture very gently using a small flame. When the initial reaction has subsided, increase the temperature slightly until most of the material has blackened. Cool, place the crucible in a large beaker, add 20 mL of hydrochloric acid R and, when the reaction has ceased, add 100 mL of water R and boil until all the copper oxide has dissolved. Filter the solution, add 400 mL of water R, heat to boiling and add 20 mL of barium chloride solution R1. Allow to stand for 2 h, filter, wash with water R, dry and ignite at about 600 ± 50 °C until 2 successive weighings do not differ by more than 0.2 per cent of the mass of the residue.
1 g of residue is equivalent to 0.1374 g of total sulfur.
Calculate the percentage content of total sulfur and subtract the percentage content of sulfur in the form of sulfate.
Sulfur in the form of sulfate
Dissolve 2.000 g in 100 mL of water R, add 2 g of cupric chloride R dissolved in 80 mL of water R and dilute to 200.0 mL with water R. Shake and filter. Heat 100.0 mL of the filtrate almost to boiling, add 1 mL of hydrochloric acid R and 5 mL of barium chloride solution R1 dropwise and heat on a water-bath. Filter, wash the precipitate with water R, dry and ignite at about 600 ± 50 °C until 2 successive weighings do not differ by more than 0.2 per cent of the mass of the residue.
1 g of residue is equivalent to 0.1374 g of sulfur present in the form of sulfate.
Calculate the percentage content of sulfur in the form of sulfate.
