Zinc Sulfate
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].
»Zinc Sulfate contains one or seven molecules of water of hydration.The monohydrate contains not less than 89.0percent and not more than 90.4percent of ZnSO4,corresponding to not less than 99.0percent and not more than 100.5percent of ZnSO4·H2O,and the heptahydrate contains not less than 55.6percent and not more than 61.0percent of ZnSO4,corresponding to not less than 99.0percent and not more than 108.7percent of ZnSO4·7H2O.
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.
Identification— Asolution of it responds to the tests for Zinc á191ñand for Sulfate á191ñ.
Acidity— Asolution containing the equivalent of 28mg of ZnSO4per mLis not colored pink by methyl orange TS.
Arsenic,Method Iá211ñ— Prepare a Test Preparationby dissolving a portion equivalent to 215mg of ZnSO4in 35mLof water:the limit is 14ppm.
Lead á251ñ— Dissolve a portion equivalent to 0.25g of ZnSO4in 5mLof water,and transfer the solution to a color-comparison tube (A).Add 10mLof Potassium Cyanide Solution(1in 10),mix,and allow the mixture to become clear.In a similar,matched color-comparison tube (B)place 5mLof water,and add 0.50mLof Standard Lead Solution(see Heavy Metals á231ñ)and 10mLof Potassium Cyanide Solution(1in 10).Add to the solution in each tube 0.1mLof sodium sulfide TS.Mix the contents of each tube,and allow to stand for 5minutes:viewed downward over a white surface,the solution in tube Ais no darker than that in tube B.The lead limit is 0.002%.
Alkalies and alkaline earths— Dissolve the equivalent of 1.12g of ZnSO4in about 150mLof water contained in a 200-mLvolumetric flask.Precipitate the zinc completely by means of ammonium sulfide TS,and dilute with water to volume.Mix,and filter through a dry filter,rejecting the first portion of the filtrate.To 100mLof the subsequent filtrate add a few drops of sulfuric acid,evaporate to dryness in a tared dish,and ignite:the weight of the residue does not exceed 5mg (0.9%).
Assay— Dissolve an accurately weighed quantity of Zinc Sulfate,equivalent to about 170mg of ZnSO4,in 100mLof water.Add 5mLof ammonia–ammonium chloride buffer TSand 0.1mLof eriochrome black TS,and titrate with 0.05Medetate disodium VSuntil the solution is deep blue in color.Each mLof 0.05Medetate disodium is equivalent to 8.072mg of ZnSO4.
Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(PA6)Pharmaceutical Analysis 6
USP28–NF23Page 2056
Phone Number:1-301-816-8389