Monographs: Pharmaceutical substances: Adeps lanae - Wool fat

Adeps lanae cum aqua

Hydrous wool fat

Hydrous wool fat is a mixture of 75% m/m of wool fat and 25% m/m of water.

Chemical name. Lanolin; CAS Reg. No. 8020-84-6.

Other name. Anhydrous lanolin, lanolin. (In certain countries the name lanolin is used to describe a formulation containing wool fat, water, and liquid paraffin.)

Description. Wool fat is a brown-yellow, unctuous mass. Hydrous wool fat is a yellowish white, unctuous mass. Odour, characteristic.

Solubility. Practically insoluble in water; soluble in ether R; slightly soluble in boiling ethanol (~750 g/l) TS.

Category. Ointment base.

Storage. Wool fat should be kept in a well-closed container.

Additional information. Melted Wool fat is a yellow, clear or almost clear liquid. On heating, Hydrous wool fat first separates into two layers, water is then driven off, and a transparent residue is formed; after cooling, a yellowish, tenacious, soft mass is produced. Melting point for Wool fat and Hydrous wool fat after drying (use the residue from the "Wool fat content"), 36-44 °C.

Requirements

Definition. Wool fat is a purified wax-like material obtained from the raw wool of sheep (Ovis aries L).

Identity tests

A. Dissolve 0.5 g in 5 ml of chloroform R and add 1 ml of acetic anhydride R and 0.1 ml of sulfuric acid (~1760 g/l) TS; a green colour is produced.

B. Dissolve 0.5 g in 5 ml of chloroform R and carefully superimpose 5 ml of sulfuric acid (~1760 g/l) TS; a bright, brown-red ring is gradually formed at the interface of the two liquids.

Acid value. Wool fat, not more than 1.0; Hydrous wool fat, not more than 0.8.

Saponification value. Reflux for 4 hours; Wool fat, 90-105; Hydrous wool fat, 67-79.

Sulfated ash. Wool fat, not more than 1.5 mg/g; Hydrous wool fat, not more than 1.0 mg/g.

Loss on drying. Dry at 105 °C for 1 hour; Wool fat loses not more than 5.0 mg/g; Hydrous wool fat loses not more than 0.32 g/g.

Wool fat content. Heat 30 g of Hydrous wool fat to constant mass on a water-bath, stirring continuously, and weigh; the residue weighs between 21.8 g and 23.3 g (72.5-77.5% m/m). (Keep the residue for "Water-absorption capacity", "Paraffins", and the melting point in "Additional information".)

Water-absorption capacity. Place 10 g of Wool fat or Hydrous wool fat after drying (use the residue from "Wool fat content") in a mortar. Using a burette, add water in portions of 0.2-0.5 ml, stirring vigorously after each addition to incorporate the water, until visible droplets separate and cannot be absorbed; not less than 20 ml of water is absorbed.

Water-soluble acid and alkaline substances. Melt 5 g of Wool fat or 6.7 g of Hydrous wool fat on a water-bath, add 75 ml of water heated to 90-95 °C, and shake vigorously for 2 minutes. Cool and filter through a filter-paper previously moistened with water. To 60 ml of the filtrate, which may show some cloudiness (keep the remaining filtrate for "Water-soluble oxidizable substances" and "Ammonia"), add 0.25 ml of bromothymol blue/ethanol TS; not more than 0.2 ml of hydrochloric acid (0.02 mol/l) VS or 0.15 ml of sodium hydroxide (0.02 mol/l) VS is required to change the colour of the indicator (blue-yellow).

Water-soluble oxidizable substances. To 10 ml of the filtrate retained in the above test add 1 ml of sulfuric acid (~100 g/l) TS and 0.1 ml of potassium permanganate (0.02 mol/l) VS, and allow to stand for 10 minutes; the colour is not completely discharged.

Paraffins. To 40 ml of dehydrated ethanol R add 0.5 g of Wool fat or Hydrous wool fat after drying (use the residue from "Wool fat content") and boil; the solution is clear or not more than opalescent.

Ammonia. To 5 ml of the filtrate from "Water-soluble acid and alkaline substances" add 0.5 ml of sodium hydroxide (1 mol/l) VS and boil; the vapours do not turn red litmus paper R to blue.