Ferric Subsulfate Solution
Fe4(OH)2(SO4)5
737.71
Basic ferric sulfate solution.
Monsel's Solution [1310-45-8].
Basic ferric sulfate solution.
Monsel's Solution [1310-45-8].
»Ferric Subsulfate Solution contains,in each 100mL,basic ferric sulfate equivalent to not less than 20g and not more than 22g of iron (Fe).Ferric Subsulfate Solution may be prepared as follows.Add 55mLof Sulfuric Acid to 800mLof water in a porcelain dish and heat to nearly 100
,then add 75mLof nitric acid,and mix.Divide 1045g of Ferrous Sulfate,coarsely powdered,into 4portions,and add these portions one at a time to the hot liquid,stirring after each addition until effervescence ceases.If,after the Ferrous Sulfate has dissolved,the solution has a black color,add nitric acid,a few drops at a time,with heating and stirring,until red fumes cease to be evolved.Boil the solution until it assumes a red color and is free from nitrate,as indicated by the test for Limit of nitratebelow,maintaining the volume at about 1000mLby the addition of water as needed.Cool,and add enough water to make the solution measure 1000mL.Filter,if necessary,until the Solution is clear.
,then add 75mLof nitric acid,and mix.Divide 1045g of Ferrous Sulfate,coarsely powdered,into 4portions,and add these portions one at a time to the hot liquid,stirring after each addition until effervescence ceases.If,after the Ferrous Sulfate has dissolved,the solution has a black color,add nitric acid,a few drops at a time,with heating and stirring,until red fumes cease to be evolved.Boil the solution until it assumes a red color and is free from nitrate,as indicated by the test for Limit of nitratebelow,maintaining the volume at about 1000mLby the addition of water as needed.Cool,and add enough water to make the solution measure 1000mL.Filter,if necessary,until the Solution is clear.
Packaging and storage—
Preserve in tight,light-resistant containers,and store at temperatures above 22.
.
Labeling—
The label indicates that crystallization may occur if the Solution is exposed to temperatures below 22,and that warming will redissolve the crystals.Label it to indicate that it is intended for topical and vaginal use only.
,and that warming will redissolve the crystals.Label it to indicate that it is intended for topical and vaginal use only.
Identification—
A:
A1in 20dilution of the Solution in water yields a brownish-red precipitate with ammonia TS.
B:
A1in 20dilution of the Solution in water yields a blue precipitate with potassium ferrocyanide TS.
C:
A1in 20dilution of the Solution in water yields a white precipitate with barium chloride TSthat is insoluble in hydrochloric acid.
Limit of nitrate—
Add a clear crystal of ferrous sulfate to a cooled mixture of equal volumes of sulfuric acid and a 1in 10dilution of the Solution in water:the crystal does not become brown,nor does a brownish-black color develop around it.
Limit of ferrous salts—
Add a few drops of freshly prepared potassium ferricyanide TSto 2mLof 1in 20dilution of the solution in water:a brown color is produced and the solution remains free from even a transient green or greenish-blue color.
Assay—
Transfer 10.0mLof the Solution to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a glass-stoppered conical flask,and add 5mLof hydrochloric acid and 3g of potassium iodide.Insert the stopper into the flask,and allow the mixture to stand for 15minutes.Add 15mLof water,and titrate the liberated iodine with 0.1Nsodium thiosulfate VS,using starch TSas the indicator.Each mLof 0.1Nsodium thiosulfate is equivalent to 5.585mg of iron (Fe).
Auxiliary Information—
Staff Liaison:Andrzej Wilk,Ph.D.,Senior Scientific Associate
Expert Committee:(PA5)Pharmaceutical Analysis 5
USP28–NF23Page 815
Pharmacopeial Forum:Volume No.28(6)Page 1789
Phone Number:1-301-816-8305