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 99.0 percent and not more than 100.5 percent 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— A solution (1 in 20) responds to the tests for Magnesium 191 and for Sulfate 191.
pH 791: between 5.0 and 9.2, in a solution (1 in 20).
Loss on drying 731— Dry it at 105 for 2 hours: the anhydrous form loses not more than 2% of its weight.
Loss on ignition 733— Weigh accurately about 1 g in a crucible, heat at 105 for 2 hours, then ignite in a muffle furnace at 450 ± 25 to 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 221— A 1.0-g portion shows no more chloride than corresponds to 0.20 mL of 0.020 N hydrochloric acid (0.014%).
Iron 241—
for magnesium sulfate intended for use in preparing nonparenteral dosage forms— Dissolve 0.50 g in 40 mL of water and proceed as directed in the test for Iron 241: the limit is 20 µg 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 1 mL of hydrochloric acid to 1000 mL with water, and mix.
Ammonium acetate solution— Transfer 250 g of ammonium acetate to a 500-mL volumetric flask, dissolve in and dilute with water to volume, and mix.
Ascorbic acid solution— Transfer 1.34 g of ascorbic acid to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix. Use this solution on the day prepared.
Color reagent— Transfer 380 mg of 3-(2-pyridyl)-5,6-di-(2-furyl)-1,2,4-triazine-5¢,5¢¢-disulfonic acid, disodium salt to a 100-mL volumetric flask, dissolve in Ammonium acetate solution, shaking by mechanical means if necessary, dilute with Ammonium acetate solution to volume, and mix. Use this solution on the day prepared.
Standard iron solution— Transfer 5.0 mL of Standard Iron Solution to a 50-mL volumetric flask, dilute with Dilute hydrochloric acid to volume, and mix. This solution contains 1.0 µg of iron per mL.
Standard preparations— To three separate 50-mL volumetric flasks transfer 2.0, 5.0, and 10.0 mL of Standard iron solution, and dilute each to 35 mL with Dilute hydrochloric acid. These solutions contain 2.0, 5.0, and 10.0 µg of iron, respectively.
Test preparation— Transfer 10.0 g of Magnesium Sulfate to a 50-mL volumetric flask, add Dilute hydrochloric acid to 35 mL, and sonicate, if necessary, to achieve complete dissolution.
Blank— Transfer 35 mL of Dilute hydrochloric acid to a 50-mL volumetric flask.
Procedure— To each of the flasks containing the Standard preparations, the Test preparation, and the Blank, add 5 mL of Ascorbic acid solution and 5 mL of Color reagent. Dilute each solution with Dilute hydrochloric acid to volume, mix, and allow to stand for 10 minutes. Concomitantly determine the absorbances of the solutions from the Standard preparations and the Test preparation at the wavelength of maximum absorbance at about 594 nm, with a suitable spectrophotometer, using the solution from the Blank to set the instrument to zero. Plot the absorbance values of the solutions from the Standard preparations versus their iron contents, in µg per 50-mL volumetric 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-mL volumetric flask, of the solution from the Test preparation. Calculate the content, in ppm, of iron in the portion of Magnesium Sulfate taken by multiplying C by 0.1: the limit is 0.5 µg per g.
Heavy metals 231— Dissolve 2 g in 25 mL of water: the limit is 0.001%.
Selenium 291— Dissolve 200 mg in 50 mL of 0.25 N nitric acid to obtain the Test Solution. The limit is 0.003%.
Assay— Weigh accurately about 250 mg of the ignited Magnesium Sulfate obtained in the test for Loss on ignition, and dissolve in 100 mL of water and the minimum amount of 3 N hydrochloric acid required for a clear solution. Adjust the reaction of the solution (using pH indicator paper; see Indicator and Test Papers under Reagents in the section Reagents, Indicators, and Solutions) with 1 N sodium hydroxide to a pH of 7, add 5 mL of ammonia–ammonium chloride buffer TS and 0.15 mL of eriochrome black TS, and titrate with 0.05 M edetate disodium VS to a blue endpoint. Each mL of 0.05 M edetate disodium is equivalent to 6.018 mg of MgSO4.
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Monograph Ravi Ravichandran, Ph.D.
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USP32–NF27 Page 2838
Pharmacopeial Forum: Volume No. 29(6) Page 1921
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.