Magnesium Sulfate
MgSO4·xH2O

Sulfuric acid magnesium salt (1:1),hydrate.
Magnesium sulfate (1:1)monohydrate 138.36

Magnesium sulfate (1:1)heptahydrate 246.48 [10034-99-8].

Anhydrous 120.37 [7487-88-9].
»Magnesium Sulfate,rendered anhydrous by ignition,contains not less than 99.0percent and not more than 100.5percent of MgSO4.
Packaging and storage— Preserve in well-closed containers.
Labeling— The label states whether it is the monohydrate,the dried form,or the heptahydrate.Magnesium Sulfate intended for use in preparing parenteral dosage forms is so labeled.Magnesium Sulfate not intended for use in preparing parenteral dosage forms is so labeled;in addition,it may be labeled also as intended for use in preparing nonparenteral dosage forms.
Identification— Asolution (1in 20)responds to the tests for Magnesium á191ñand for Sulfate á191ñ.
pHá791ñ: between 5.0and 9.2,in a solution (1in 20).
Loss on drying á731ñ— Dry it at 105for 2hours:the anhydrous form loses not more than 2%of its weight.
Loss on ignition á733ñ— Weigh accurately about 1g in a crucible,heat at 105for 2hours,then ignite in a muffle furnace at 450±25to constant weight:the monohydrate loses between 13.0%and 16.0%of its weight,the dried form loses between 22.0%and 28.0%of its weight,and the heptahydrate loses between 40.0%and 52.0%of its weight.
Chloride á221ñ— A1.0-g portion shows no more chloride than corresponds to 0.20mLof 0.020Nhydrochloric acid (0.014%).
Iron á241ñ—
FOR MAGNESIUM SULFATE INTENDED FOR USE IN PREPARING NONPARENTERAL DOSAGE FORMS— Dissolve 0.50g in 40mLof water and proceed as directed in the test for Iron á241ñ:the limit is 20µg per g.
FOR MAGNESIUM SULFATE INTENDED FOR USE IN PREPARING PARENTERAL DOSAGE FORMS— [NOTE—Rinse all glassware used in this test with Dilute hydrochloric acid.]
Dilute hydrochloric acid— Dilute 1mLof hydrochloric acid to 1000mLwith water,and mix.
Ammonium acetate solution— Transfer 250g of ammonium acetate to a 500-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.
Ascorbic acid solution— Transfer 1.34g of ascorbic acid to a 100-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Use this solution on the day prepared.
Color reagent— Transfer 380mg of 3-(2-pyridyl)-5,6-di-(2-furyl)-1,2,4-triazine-5¢,5¢¢-disulfonic acid,disodium salt to a 100-mLvolumetric flask,dissolve in Ammonium acetate solution,shaking by mechanical means if necessary,dilute with Ammonium acetate solutionto volume,and mix.Use this solution on the day prepared.
Standard iron solution— Transfer 5.0mLof Standard Iron Solutionto a 50-mLvolumetric flask,dilute with Dilute hydrochloric acidto volume,and mix.This solution contains 1.0µg of iron per mL.
Standard preparations— To three separate 50-mLvolumetric flasks transfer 2.0,5.0,and 10.0mLof Standard iron solution,and dilute each to 35mLwith Dilute hydrochloric acid.These solutions contain 2.0,5.0,and 10.0µg of iron,respectively.
Test preparation— Transfer 10.0g of Magnesium Sulfate to a 50-mLvolumetric flask,add Dilute hydrochloric acidto 35mL,and sonicate,if necessary,to achieve complete dissolution.
Blank— Transfer 35mLof Dilute hydrochloric acidto a 50-mLvolumetric flask.
Procedure— To each of the flasks containing the Standard preparations,the Test preparation,and the Blank,add 5mLof Ascorbic acid solutionand 5mLof Color reagent.Dilute each solution with Dilute hydrochloric acidto volume,mix,and allow to stand for 10minutes.Concomitantly determine the absorbances of the solutions from the Standard preparationsand the Test preparationat the wavelength of maximum absorbance at about 594nm,with a suitable spectrophotometer,using the solution from the Blankto set the instrument to zero.Plot the absorbance values of the solutions from the Standard preparationsversus their iron contents,in µg per 50-mLvolumetric flask,and draw the straight line best fitting the three plotted points.From the graph so obtained determine the iron content,C,in µg per 50-mLvolumetric flask,of the solution from the Test preparation.Calculate the content,in ppm,of iron in the portion of Magnesium Sulfate taken by multiplying Cby 0.1:the limit is 0.5µg per g.
Heavy metals á231ñ— Dissolve 2g in 25mLof water:the limit is 0.001%.
Selenium á291ñ— Dissolve 200mg in 50mLof 0.25Nnitric acid to obtain the Test Solution.The limit is 0.003%.
Assay— Weigh accurately about 250mg of the ignited Magnesium Sulfate obtained in the test for Loss on ignition,and dissolve in 100mLof water and the minimum amount of 3Nhydrochloric acid required for a clear solution.Adjust the reaction of the solution (using pHindicator paper;see Indicator and Test Papersunder Reagentsin the section Reagents,Indicators,and Solutions)with 1Nsodium hydroxide to a pHof 7,add 5mLof ammonia–ammonium chloride buffer TSand 0.15mLof eriochrome black TS,and titrate with 0.05Medetate disodium VSto a blue endpoint.Each mLof 0.05Medetate disodium is equivalent to 6.018mg of MgSO4.
Auxiliary Information— Staff Liaison:Ravi Ravichandran,Ph.D.,Senior Scientist
Expert Committee:(PA3)Pharmaceutical Analysis 3
USP28–NF23Page 1175
Pharmacopeial Forum:Volume No.29(6)Page 1921
Phone Number:1-301-816-8330