DEFINITION
Zinc Cream contains 32% w/w of Zinc Oxide in a suitable water-in-oil emulsified basis.
Extemporaneous preparation
The following formula and directions apply.
| Zinc Oxide, finely sifted | 320 g |
| Calcium Hydroxide | 0.45 g |
| Oleic Acid | 5 mL |
| Arachis Oil | 320 mL |
| Wool Fat | 80 g |
| Purified Water, freshly boiled and cooled Sufficient to produce | 1000 g |
Mix the Zinc Oxide and the Calcium Hydroxide, triturate to a smooth paste with a mixture of the Oleic Acid and Arachis Oil, incorporate the Wool Fat and add gradually with continuous stirring sufficient Purified Water to produce 1000 g.
The suitability of the Cream for use as a diluent should be confirmed before use.
The cream complies with the requirements stated under Topical Semi-solid Preparations and with the following requirements.
Content of zinc oxide, ZnO
30.0 to 34.0% w/w.
IDENTIFICATION
The residue obtained in the Assay is yellow when hot and white when cool.
ASSAY
Heat 0.5 g of the cream gently in a porcelain dish over a small flame until the basis is completely volatilised or charred.
Increase the heat until all the carbon is removed. Dissolve the residue in 10 mL of 2M acetic acid and add sufficient water to produce 50 mL. To the resulting solution add 50 mg of xylenol orange triturate and sufficient hexamine to produce a violet-pink colour. Add a further 2 g of hexamine and titrate with 0.1M disodium edetate VS until the solution becomes
yellow. Each mL of 0.1M disodium edetate VS is equivalent to 8.138 mg of ZnO.
