Ferric Oxide
»Ferric Oxide contains not less than 97.0percent and not more than 100.5percent of Fe2O3,calculated on the ignited basis.
Packaging and storage— Preserve in well-closed containers.
Identification— Dissolve 0.5g in 50mLof hydrochloric acid,and dilute with water to 200mL:the solution so obtained responds to the test for Ferric Saltsunder Iron á191ñ.
Water-soluble substances— Digest 2.0g in 100mLof water on a boiling water bath for 2hours,filter,and wash the filter with water.Evaporate the filtrate and washings,and dry the residue at 105for 1hour:the weight of the dried residue is not more than 20mg (1.0%).
Acid-insoluble substances— Digest 2.0g in 25mLof hydrochloric acid by boiling for 20minutes.Add 100mLof hot water and filter quantitatively through a tared filtering crucible,with the aid of hot wash water until the filtrate tests negative for chloride.Dry the crucible and contents at 105for 1hour:the residue weighs not more than 2mg (0.1%).
Organic colors and lakes— Place 1.0g in each of 3beakers,and add 25mLof each of the following reagents,respectively:1-chloronaphthalene,alcohol,and chloroform.Heat the beakers containing alcohol and chloroform just to boiling.Heat the other beaker on a boiling water bath for 15minutes,with occasional swirling.Filter the contents of the beakers through retentive,solvent-resistant filter paper.If any of the filtrates shows visible turbidity,centrifuge for 15minutes.Record the spectra against respective solvent blanks in 1-cm cells from 350to 750nm.No peak,above the noise level,with a slope greater than +0.001absorbance unit per nm is found.
Mercury,Method IIa á261ñ— Transfer 0.67g of Ferric Oxide to a beaker,add 35mLof 0.5Nhydrochloric acid,and heat to boiling.Allow to cool,and proceed as directed for Test Preparationbeginning with “Add 2drops of phenolphthalein.”The limit is 3µg per g.
Limit of arsenic—
Lead acetate cotton— Immerse absorbent cotton pledgets in a mixture of lead acetate TSand 2Nacetic acid (10:1).Free the cotton pledgets from excess liquid by expression,and allow to air-dry.
Sodium borohydride solution— Dissolve 3g of sodium borohydride in 0.25Nsodium hydroxide,dilute with 0.25Nsodium hydroxide to obtain 100mLof solution,and mix.Store in a loosely covered container protected from direct sunlight.
Mercuric bromide paper— Immerse several 15-mm diameter filter paper disks in alcoholic mercuric bromide TS,remove the disks from the solution,and allow to dry,protected from light.Store in a glass-stoppered container protected from light.
Arsenic trioxide stock solution— Transfer 132.0mg of arsenic trioxide to a 100-mLvolumetric flask,dissolve in 2.0mLof 2Nsodium hydroxide,dilute with water to volume,and mix.
Standard solution— On the day of use,transfer 1.0mLof the Arsenic trioxide stock solutionto a 1000-mLvolumetric flask,dilute with water to volume,and mix.Dilute 1.5mLof this solution with hydrochloric acid to 10.0mL,and mix.This solution contains 0.15µg of arsenic per mL.
Test solution— Dissolve 0.5g of Ferric Oxide in several mLof hydrochloric acid with the aid of heat,dilute with hydrochloric acid to 10.0mL,and mix.
Apparatus— Prepare a 300-mLside-arm conical flask containing a magnetic stirring bar.Attach to the conical flask a ground-glass stopper through which passes a 20-cm long glass tube with an internal diameter of 5mm.The lower end of the tube is inside the conical flask,and has been drawn to a tip with an internal diameter of 1mm.About 15mm from the tip and at least 3mm below the lower surface of the stopper is an orifice about 2.5mm in diameter.The upper end of the tube has a flat ground surface at a right angle to the axis of the tube.Asecond glass tube of the same internal diameter and 30mm long,with a similar flat ground surface,is placed in contact with the ground surface of the first tube and is held in position by a clamp and springs.Into the lower tube insert about 55mg of loosely packed Lead acetate cotton.Between the flat surfaces of the tubes place a disk of Mercuric bromide paper.
Procedure— Before placing the tube assembly into the flask,transfer the Test solutionto the flask,and add 5.0mLof potassium iodide TSand 20mLof water.Assemble the apparatus immediately,and stir while slowly adding through the side arm of the flask over a period of about 20minutes 40mLof Sodium borohydride solution.Examine the stain produced on the Mercuric bromide paper.Perform the same procedure using the Standard solution.The stain produced on the Mercuric bromide paperfrom the Test solutionis not more intense than that from the Standard solution(3µg per g).
Limit of lead—
Lead nitrate stock solution— Transfer 159.8mg of lead nitrate to a 100-mLvolumetric flask,dissolve in and dilute with 0.5Mnitric acid to volume,and mix.Prepare and store this solution in glass containers free from soluble lead salts.
Standard solution— On the day of use,transfer 5.0mLof the Lead nitrate stock solutionto a 100-mLvolumetric flask,add 10mLof 1Nhydrochloric acid,dilute with water to volume,and mix.Transfer 1.0mLof this solution to a second 100-mLvolumetric flask,add 10mLof 1Nhydrochloric acid,dilute with water to volume,and mix.This solution contains 0.5µg of lead per mL.
Test solution— Transfer 2.5g of Ferric Oxide to a 100-mLglass-stoppered conical flask,add 35mLof 0.1Nhydrochloric acid,and stir for 1hour.Filter,collecting the filtrate in a 50-mLvolumetric flask,dilute with 0.1Nhydrochloric acid to volume,and mix.
Procedure— Concomitantly determine the absorbance of the Standard solutionand the Test solutionat the lead emission line of 217.0nm with an atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with a lead hollow-cathode lamp,a flow spoiler,and an air–acetylene oxidizing flame.The absorbance of the Test solutiondoes not exceed that of the Standard solution(0.001%).
Assay— Digest about 1.5g of Ferric Oxide,accurately weighed,in 25mLof hydrochloric acid on a water bath until dissolved.Add 10mLof hydrogen peroxide TS,and evaporate on a water bath almost to dryness in order to volatilize all hydrogen peroxide.Dissolve the residue by warming with 5mLof hydrochloric acid,add 25mLof water,filter into a 250-mLvolumetric flask,washing the filter with water,and add water to volume.Transfer a 50-mLaliquot to a glass-stoppered flask,add 3g of potassium iodide and 5mLof hydrochloric acid,and insert the stopper in the flask.Allow the mixture to stand for 15minutes,add 50mLof water,and titrate the liberated iodine with 0.1Nsodium thiosulfate VS,using starch TSas the indicator.Perform a blank test with the same quantities of reagents and in the same manner,and make any necessary corrections.Each mLof 0.1Nsodium thiosulfate is equivalent to 7.985mg of Fe2O3.Ignite about 2g of Ferric Oxide at 800±25to constant weight as directed under Loss on Ignition á733ñ,to enable calculation of percentage Fe2O3on the ignited basis.[NOTE—Ignited Ferric Oxide is hygroscopic.]
Auxiliary Information— Staff Liaison:Catherine Sheehan,B.Sc.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 3006
Pharmacopeial Forum:Volume No.28(3)Page 720
Phone Number:1-301-816-8262