Ferric Sulfate
Fe2(SO4)3·xH2O(anhydrous) 399.88

Ferric persulfate.
Ferric sesquisulfate.
Ferric tersulfate [10028-22-5].

Hydrate [142906-29-4].
»Ferric Sulfate is hydrated Fe2(SO4)3.It contains not less than 73.0percent and not more than 80.0percent of Fe2(SO4)3.
Packaging and storage— Preserve in tight,light-resistant containers,and store at controlled room temperature.
Labeling— Label it to indicate that it is intended for use in compounding topical and periodontal dosage forms only.
Identification— Dissolve 0.5g in a mixture of 50mLof water and 3mLof hydrochloric acid:this solution meets the requirements for the Ferric Saltstest under Iron á191ñ.
Limit of insoluble matter— Transfer 10g in a covered beaker,and dissolve in a mixture of 100mLof water and 5mLof sulfuric acid.Heat to boiling,and warm on a steam bath for 1hour.Filter the hot solution through a tared sintered-glass crucible of fine porosity.Wash the beaker and the filter with hot water,dry the crucible at 105,cool in a desiccator,and weigh:not more than 2mg of insoluble matter is found (0.02%).
Limit of chloride— Dissolve 1g by warming with a mixture of 10mLof water and 1mLof nitric acid,add 4mLof additional nitric acid,and dilute with water to 50mL.To 25mLof this solution add 1mLof phosphoric acid and 1mLof silver nitrate TS.Any turbidity does not exceed that produced in a control containing 0.01mg of chloride ion (Cl),1mLof nitric acid,1mLof phosphoric acid,and 1mLof silver nitrate TS(0.002%).
Limit of ferrous iron— Dissolve 4g by warming with 50mLof dilute sulfuric acid (1in 10),cool,and titrate with 0.1Npotassium permanganate:not more than 0.16mLis required to produce a permanent pink color (0.02%as Fe++).
Limit of copper and zinc— [NOTE—If the reagents used in the tests for Copper and Zinccontain excessive amounts of copper and zinc,then they should first be purified by extracting with Dithizone Extraction Solution (see Lead á251ñ).]
Copper— Dissolve 1.2g in 100mLof water.To 10mLof this test solution add 50mLof a solution containing 5g of ammonium tartrate and 5mLof ammonium hydroxide.Add 10mLof Standard Dithizone Solution(see Lead á251ñ),shake for 2minutes,draw off the dithizone layer,and compare the pink color with that in a control containing 6µg of copper ion (Cu)and treated exactly as the 10-mLportion of test solution.If the color in the test solution is less than that in the control,then less than 0.005%of Cu and of Zn is found and the test for Zincis not necessary.If the color in the test solution is more than that in the control,add 15mLof dilute hydrochloric acid (1in 250),and shake for 2minutes.Draw off the dithizone solution,and shake with a second 15mLof dilute hydrochloric acid (1in 250)for 2minutes.[NOTE—Draw off the dithizone,combine the two acid extracts,and reserve for the test for Zinc.]Any pink color in the dithizone solution is not darker than that in the control solution treated exactly as the test solution (0.005%).
Zinc— To the combined acid extracts saved from the test for Copper,add sufficient 0.5Msodium acetate to bring the pHto between 5.0and 5.5,and then add 1mLof 0.1Nsodium thiosulfate.Add 10mLof Standard Dithizone Solution(see Lead á251ñ),shake for 2minutes,and allow the layers to separate.Draw off the dithizone layer,and discard the water layer.Any pink color in the dithizone layer is not greater than that in a control prepared by adding 0.006mg of zinc ion (Zn)to the combined acid extracts from the control used in the test for Copper(0.005%).
Limit of nitrate— Dissolve 10g in 100mLof dilute sulfuric acid (1in 100),heat to boiling,and pour,slowly,into a mixture of 140mLof water and 50mLof ammonium hydroxide.Pass through a folded filter while still hot,wash the filter with hot water until the volume of filtrate is 300mL,mix,and cool.To 15mLof the diluted filtrate add 1mLof sodium chloride solution (1in 200),0.10mLof indigo carmine TS,and 15mLof sulfuric acid.The blue color is not completely discharged at the end of 5minutes (0.01%).
Substances not precipitated by ammonia— Evaporate to dryness 30mLof the diluted filtrate obtained in the test for Limit of nitrate,and ignite gently:the weight of residue does not exceed 1mg (0.1%).
Assay— Transfer about 700mg of Ferric Sulfate,accurately weighed,to a glass-stoppered conical flask.Add a mixture of 50mLof water and 3mLof hydrochloric acid,and swirl to dissolve.Add 3g of potassium iodide,insert the stopper into the flask,and allow to stand in the dark for 30minutes.Then add 100mLof water,and titrate the liberated iodine with 0.1Nsodium thiosulfate VS,adding starch TSas the endpoint is approached.Each mLof 0.1Nsodium thiosulfate is equivalent to 19.994mg of ferric sulfate [Fe2(SO4)3].
Auxiliary Information— Staff Liaison:Andrzej Wilk,Ph.D.,Senior Scientific Associate
Expert Committee:(PA5)Pharmaceutical Analysis 5
USP28–NF23Page 816
Pharmacopeial Forum:Volume No.28(6)Page 1790
Phone Number:1-301-816-8305