ZnO 81.39

Zinc oxide.
Zinc oxide [1314-13-2].

Packaging and storage— Preserve in well-closed containers.

Identification—

Alkalinity— Mix 1.0 g with 10 mL of hot water, add 2 drops of phenolphthalein TS, and filter: if a red color is produced, not more than 0.30 mL of 0.10 N hydrochloric acid is required to discharge it.

Loss on ignition 733— Weigh accurately about 2 g, and ignite at 500 to constant weight: it loses not more than 1.0% of its weight.

Carbonate and color of solution— Mix 2.0 g with 10 mL of water, add 30 mL of 2 N sulfuric acid, and heat on a steam bath, with constant stirring: no effervescence occurs and the resulting solution is clear and colorless.

Arsenic, Method I 211: 6 ppm.

Lead— Add 2 g to 20 mL of water, stir well, add 5 mL of glacial acetic acid, and warm on a steam bath until solution is effected: the addition of 5 drops of potassium chromate TS produces no turbidity or precipitate.

Iron and other heavy metals— Cool two separate 5-mL portions of the solution obtained in the test for Carbonate and color of solution. White precipitates are formed when potassium ferrocyanide TS is added to the first portion and when sodium sulfide TS is added to the second portion.

Assay— Dissolve about 1.5 g of freshly ignited Zinc Oxide, accurately weighed, and 2.5 g of ammonium chloride in 50.0 mL of 1 N sulfuric acid VS with the aid of gentle heat, if necessary. When solution is complete, add methyl orange TS, and titrate the excess sulfuric acid with 1 N sodium hydroxide VS. Each mL of 1 N sulfuric acid is equivalent to 40.69 mg of ZnO.

Topic/Question	Contact	Expert Committee
Monograph	Feiwen Mao, M.S. Scientist 1-301-816-8320	(MDOOD05) Monograph Development-Ophthalmics Oncologics and Dermatologicals

USP32–NF27 Page 3896