Zinc Oxide
ZnO 81.39

Zinc oxide.
Zinc oxide [1314-13-2].
»Zinc Oxide,freshly ignited,contains not less than 99.0percent and not more than 100.5percent of ZnO.
Packaging and storage— Preserve in well-closed containers.
Identification—
A: When strongly heated,it assumes a yellow color that disappears on cooling.
B: Asolution of it in a slight excess of 3Nhydrochloric acid responds to the tests for Zinc á191ñ.
Alkalinity— Mix 1.0g with 10mLof hot water,add 2drops of phenolphthalein TS,and filter:if a red color is produced,not more than 0.30mLof 0.10Nhydrochloric acid is required to discharge it.
Loss on ignition á733ñ— Weigh accurately about 2g,and ignite at 500to constant weight:it loses not more than 1.0%of its weight.
Carbonate and color of solution— Mix 2.0g with 10mLof water,add 30mLof 2Nsulfuric acid,and heat on a steam bath,with constant stirring:no effervescence occurs and the resulting solution is clear and colorless.
Lead— Add 2g to 20mLof water,stir well,add 5mLof glacial acetic acid,and warm on a steam bath until solution is effected:the addition of 5drops of potassium chromate TSproduces no turbidity or precipitate.
Iron and other heavy metals— Cooled 5-mLportions of the solution obtained in the test for Carbonate and color of solutionyield white precipitates with potassium ferrocyanide TSand with sodium sulfide TS.
Assay— Dissolve about 1.5g of freshly ignited Zinc Oxide,accurately weighed,and 2.5g of ammonium chloride in 50.0mLof 1Nsulfuric acid VSwith the aid of gentle heat,if necessary.When solution is complete,add methyl orange TS,and titrate the excess sulfuric acid with 1Nsodium hydroxide VS.Each mLof 1Nsulfuric acid is equivalent to 40.69mg of ZnO.
Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(PA6)Pharmaceutical Analysis 6
USP28–NF23Page 2054
Phone Number:1-301-816-8389