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Zinc Oxide
ZnO 81.39

Zinc oxide.
Zinc oxide [1314-13-2].
» Zinc Oxide, freshly ignited, contains not less than 99.0 percent and not more than 100.5 percent of ZnO.
Packaging and storage— Preserve in well-closed containers.
A: When strongly heated, it assumes a yellow color that disappears on cooling.
B: A solution of it in a slight excess of 3 N hydrochloric acid responds to the tests for Zinc 191.
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.
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.
Change to read:
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.USP29
Residual solvents 467: meets the requirements.
(Official January 1, 2007)
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.
Auxiliary Information— Staff Liaison : Feiwen Mao, M.S., Senior Scientific Associate
Expert Committee : (MDOOD05) Monograph Development-Ophthalmics Oncologics and Dermatologicals
USP29–NF24 Page 2289
Pharmacopeial Forum : Volume No. 31(1) Page 80
Phone Number : 1-301-816-8320