Zinc Oxide
(zink ox' ide).

ZnO 81.39
Zinc oxide     [1314-13-2].
Zinc Oxide, freshly ignited, contains NLT 99.0% and NMT 100.5% of ZnO.
•  A. When strongly heated, it assumes a yellow color that disappears on cooling.
•  B. Identification Tests—General, Zinc 191
Sample solution:  Dissolve in a slight excess of 3 N hydrochloric acid.
Acceptance criteria:  Meets the requirements
•  Procedure
Sample:  1.5 g, freshly ignited
Analysis:  Dissolve the Sample 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. 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.
Acceptance criteria:  99.0%–100.5% on the ignited basis
•  Arsenic, Method I 211: NMT 6 ppm
•  Lead
Sample solution:  Add 2 g to 20 mL of water, stir well, and add 5 mL of glacial acetic acid. Warm on a steam bath until dissolved.
Analysis:  Add 5 drops of potassium chromate TS.
Acceptance criteria:  No turbidity or precipitate is produced.
•  Iron and Other Heavy Metals
Sample solution:  Use the solution from Carbonate and Color of Solution.
Analysis:  Cool 2 separate 5-mL aliquots of the Sample solution. Add potassium ferrocyanide TS to the first aliquot, and add sodium sulfide TS to the second aliquot.
Acceptance criteria:  White precipitates are formed in both aliquots.
•  Loss on Ignition 733: Ignite 2 g at 500 to constant weight: it loses NMT 1.0% of its weight.
•  Alkalinity
Analysis:  Mix 1.0 g with 10 mL of hot water, add 2 drops of phenolphthalein TS, and filter.
Acceptance criteria:  If a red color is produced, NMT 0.30 mL of 0.10 N hydrochloric acid is required to discharge it.
•  Carbonate and Color of Solution
Analysis:  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.
Acceptance criteria:  No effervescence occurs, and the resulting solution is clear and colorless. [Note—Use this solution in the test for Iron and Other Heavy Metals. ]
•  Packaging and Storage: Preserve in well-closed containers.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Feiwen Mao, M.S.
Senior Scientific Liaison
(SM32010) Monographs - Small Molecules 3
USP35–NF30 Page 5073
Pharmacopeial Forum: Volume No. 31(1) Page 80