DEFINITION
Zinc Ointment contains 15% w/w of Zinc Oxide in a suitable water-emulsifying basis.
Extemporaneous preparation
The following formula and directions apply.
| Zinc Oxide, finely sifted | 150 g |
| Simple Ointment | 850 g |
Triturate the Zinc Oxide with a portion of the Simple Ointment until smooth, gradually add the remainder of the Simple Ointment and mix thoroughly.
The ointment complies with the requirements stated under Topical Semi-solid Preparations and with the following requirements.
Content of zinc oxide, ZnO
14.0 to 16.0% w/w.
IDENTIFICATION
The residue obtained in the Assay is yellow when hot and white when cool.
ASSAY
Heat 0.5 g of the ointment 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 0.05M disodium edetate VS until the solution becomes
yellow. Each mL of 0.05M disodium edetate VS is equivalent to 4.069 mg of ZnO.
