Lanolin
(Ph. Eur. monograph 0135)
DEFINITION
Mixture of 75 per cent m/m of wool fat and 25 per cent m/m of water. It is obtained by the gradual addition of water to melted wool fat with continuous stirring. A suitable antioxidant may be added.
CHARACTERS
Appearance
Pale yellow, unctuous substance.
IDENTIFICATION
A. In a test-tube, dissolve 0.5 g in 5 mL of methylene chloride R and add 1 mL of acetic anhydride R and
0.1 mL of sulfuric acid R. A green colour develops.
B. Dissolve 50 mg in 5 mL of methylene chloride R, add 5 mL of sulfuric acid R and shake. A red colour develops and an intense green fluorescence appears in the lower layer when examined in daylight, with illumination from behind the observer.
TESTS
Water-soluble acid or alkaline substances
Melt 6.7 g on a water-bath and shake vigorously for 2 min with 75 mL of water R previously heated to 90-95 °C. Allow to cool and filter through filter paper previously rinsed with water R. To 60 mL of the filtrate (which may not be clear) add 0.25 mL of bromothymol blue solution R1. Not more than 0.2 mL of 0.02 M hydrochloric acid or 0.15 mL of 0.02 M sodium hydroxide is required to change the colour of the indicator.
Drop point (2.2.17)
38 °C to 44 °C.
To fill the metal cup, melt the residue obtained in the test for wool-fat content on a water-bath, cool to about 50 °C, pour into the cup and allow to stand at 15-20 °C for 24 h.
Water-absorption capacity
Place 10 g of the residue obtained in the test for wool-fat content in a mortar. Add water R in portions of 0.2-0.5 mL from a burette, stirring vigorously after each addition to incorporate the water R. The end-point is reached when visible droplets remain which cannot be incorporated. Not less than 20 mL of water R is absorbed.
Acid value (2.5.1)
Maximum 0.8, determined on 5.0 g dissolved in 25 mL of the prescribed mixture of solvents.
Peroxide value (2.5.5, Method A)
Maximum 15.
Saponification value (2.5.6)
67 to 79, determined on 2.00 g while heating under reflux for 4 h.
Water-soluble oxidisable substances
To 10 mL of the filtrate obtained in the test for water-soluble acid or alkaline substances add 1 mL of dilute sulfuric acid R and 0.1 mL of 0.02 M potassium permanganate. After 10 min, the solution is not completely decolourised.
Paraffins
Maximum 1.0 per cent.
The tap and cotton plugs used must be free from grease Prepare a column of anhydrous aluminium oxide 230 mm long and 20 mm in diameter by adding a slurry of anhydrous aluminium oxide R and light petroleum R1 to a glass tube fitted with a tap and containing light petroleum R1. Allow to settle and reduce the depth of the layer of solvent above the column to about 40 mm. Dissolve 3.0 g of the residue obtained in the test for wool-fat content in 50 mL of warm light petroleum R1, cool, pass the solution through the column at a rate of 3 mL/min and wash with 250 mL of light petroleum R1. Concentrate the combined eluate and washings to low bulk by distillation, evaporate to dryness on a water-bath and heat the residue at 105 °C for periods of 10 min until 2 successive weighings do not differ by more than 1 mg. The residue weighs a maximum of 30 mg.
Chlorides
Maximum 115 ppm.
Boil 1.3 g with 20 mL of ethanol (90 per cent V/V) R under a reflux condenser for 5 min. Cool, add 40 mL of water R and 0.5 mL of nitric acid R and filter.
To the filtrate add 0.15 mL of a 10 g/L solution of silver nitrate R in ethanol (90 per cent V/V) R. Allow to stand for 5 min, protected from light. Any opalescence in the solution is not more intense than that in a standard prepared at the same time by adding 0.15 mL of a 10 g/L solution of silver nitrate R in ethanol (90 per cent V/V) R to a mixture of 0.2 mL of 0.02 M hydrochloric acid, 20 mL of ethanol (90 per cent V/V) R, 40 mL of water R and 0.5 mL of nitric acid R.
Sulfated ash (2.4.14)
Maximum 0.1 per cent.
Ignite 5.0 g and use the residue.
Wool-fat content
72.5 per cent to 77.5 per cent.
In a suitable tared dish containing a glass rod, heat 30.0 g to constant mass on a water-bath, stirring continuously. Weigh the residue.
STORAGE
At a temperature not exceeding 25 °C.
