Compound Zinc Paste

Compound Zinc Paste contains 25% w/w each of Zinc Oxide and Starch in a suitable hydrophobic basis.

The following formula and directions apply.

Melt the White Soft Paraffin, incorporate the Zinc Oxide and the Starch and stir until cold.

The paste complies with the requirements stated under Topical Semi-solid Preparations and with the following requirements.

23.5 to 26.5% w/w.

The residue obtained in the Assay is yellow when hot and white when cool.

Heat 0.5 g of the paste 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.