Zinc Sulfate
(zink sul' fate).

ZnSO4·xH2O
Sulfuric acid, zinc salt (1:1), hydrate;    
Zinc sulfate (1:1) monohydrate     179.46
Zinc sulfate (1:1) heptahydrate     287.56 [7446-20-0].
Anhydrous     161.46 [7733-02-0].
DEFINITION
Zinc Sulfate contains one or seven molecules of water of hydration. The monohydrate contains NLT 89.0% and NMT 90.4% of ZnSO4, corresponding to NLT 99.0% and NMT 100.5% of ZnSO4·H2O, and the heptahydrate contains NLT 55.6% and NMT 61.0% of ZnSO4, corresponding to NLT 99.0% and NMT 108.7% of ZnSO4·7H2O.
IDENTIFICATION
•  A. Identification Tests—General, Zinc 191: Meets the requirements
•  B. Identification Tests—General, Sulfate 191: Meets the requirements
ASSAY
•  Procedure
Sample solution:  Equivalent to 1.70 mg/mL of ZnSO4 in water
Analysis:  To 100 mL of the Sample solution add 5 mL of ammonia–ammonium chloride buffer TS and 0.1 mL of eriochrome black TS, and titrate with 0.05 M edetate disodium VS until the solution is deep blue in color. Each mL of 0.05 M edetate disodium is equivalent to 8.072 mg of ZnSO4.
Acceptance criteria 
Monohydrate:  89.0%–90.4% of ZnSO4, corresponding to 99.0%–100.5% of ZnSO4·H2O
Heptahydrate:  55.6%–61.0% of ZnSO4, corresponding to 99.0%–108.7% of ZnSO4·7H2O
IMPURITIES
•  Limit of Arsenic, Method I 211
Test preparation:  Dissolve a portion equivalent to 215 mg of ZnSO4 in 35 mL of water.
Acceptance criteria:  NMT 14 ppm
•  Limit of Lead 251
Standard solution:  Combine 5 mL of water, 0.50 mL of Standard Lead Solution (see Heavy Metals 231), and 10 mL of Potassium Cyanide Solution (1 in 10) in a color-comparison tube.
Test preparation:  Dissolve an amount equivalent to 0.25 g of ZnSO4 in 5 mL of water, and transfer the solution to a similar, matched color-comparison tube. Add 10 mL of Potassium Cyanide Solution (1 in 10) and allow the mixture to become clear.
Analysis:  To the Standard solution and the Test preparation add 0.1 mL of sodium sulfide TS. Mix the contents of each tube, and allow to stand for 5 min.
Acceptance criteria:  Viewed downward over a white surface, the Test preparation is not darker than the Standard solution (NMT 20 ppm of lead).
•  Alkalies and Alkaline Earths
Sample solution:  Dissolve the equivalent of 1.12 g of ZnSO4 in 150 mL of water contained in a 200-mL volumetric flask. Add sufficient ammonium sulfide TS to precipitate the zinc completely, and dilute with water to volume. Pass through a dry filter, and reject the first portion of the filtrate.
Analysis:  To 100 mL of the Sample solution filtrate add a few drops of sulfuric acid, evaporate to dryness in a tared dish, and ignite.
Acceptance criteria:  The weight of the residue is NMT 5 mg (0.9%).
SPECIFIC TESTS
•  Acidity
Sample solution:   28 mg/mL of ZnSO4
Acceptance criteria:   The Sample solution is not colored pink by methyl orange TS.
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight containers.
•  Labeling: The label indicates whether it is the monohydrate or the heptahydrate. Label any oral or parenteral preparations containing Zinc Sulfate to state the content of elemental zinc.
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
1-301-816-8320
(SM32010) Monographs - Small Molecules 3
USP35–NF30 Page 5076