Magnesium Oxide
MgO 40.30

Magnesium oxide.
Magnesium oxide [1309-48-4].
» Magnesium Oxide, after ignition, contains not less than 96.0 percent and not more than 100.5 percent of MgO.
Packaging and storage— Preserve in tight containers.
Labeling— Label it to indicate its bulk density. The indicated density may be in the form of a range.
Identification— A solution in diluted hydrochloric acid meets the requirements of the tests for Magnesium 191.
Loss on ignition 733 Transfer to a tared platinum crucible about 500 mg, weigh accurately, and ignite at 800 ± 25 to constant weight: it loses not more than 10.0% of its weight.
Free alkali and soluble salts— Boil 2.0 g with 100 mL of water for 5 minutes in a covered beaker, and filter while hot. To 50 mL of the cooled filtrate add methyl red TS, and titrate with 0.10 N sulfuric acid: not more than 2.0 mL of the acid is consumed. Evaporate 25 mL of the remaining filtrate to dryness, and dry at 105 for 1 hour: not more than 10 mg of residue remains (2.0%).
Acid-insoluble substances— Mix 2 g with 75 mL of water, add hydrochloric acid in small portions, with agitation, until no more dissolves, and boil for 5 minutes. If an insoluble residue remains, filter, wash well with water until the last washing is free from chloride, and ignite: the weight of the ignited residue does not exceed 2 mg (0.1%).
Limit of calcium—
Dilute hydrochloric acid, Lanthanum solution, Standard preparations, and Blank solution— Prepare as directed in the test for Limit of calcium under Magnesium Carbonate.
Test preparation— Transfer 250 mg of Magnesium Oxide, freshly ignited, to a beaker, add 30 mL of Dilute hydrochloric acid, and stir until dissolved, heating if necessary. Transfer the solution so obtained to a 200-mL volumetric flask containing 4 mL of Lanthanum solution, dilute with water to volume, and mix.
Procedure— Proceed as directed in the test for Limit of calcium under Magnesium Carbonate. Determine the concentration, C, in µg per mL, of calcium in the Test preparation using the calibration graph. Calculate the content of calcium, in percentage, in the portion of Magnesium Oxide taken by the formula:
in which C is as defined above; the multiplier of 0.001 is for conversion of µg per mL to mg per mL; V is the volume, in mL, of the Test preparation; and W is the amount of Magnesium Oxide, in mg, taken to prepare the Test preparation: the limit is 1.1%.
Heavy metals 231 Dissolve 2.0 g in 35 mL of 3 N hydrochloric acid, and evaporate the solution on a steam bath to dryness. Toward the end of the evaporation, stir frequently to disintegrate the residue so that finally a dry powder is obtained. Dissolve the residue in 20 mL of water, and evaporate to dryness in the same manner as before. Redissolve the residue in 20 mL of water, filter if necessary, and dilute with water to 40 mL. To 20 mL add water to make 25 mL: the limit is 20 µg per g.
Iron 241 Boil 40 mg with 5 mL of 2 N nitric acid for 1 minute. Cool, dilute with water to 50 mL, and mix. Dilute 25 mL of this solution with water to 45 mL, and add 2 mL of hydrochloric acid: the limit is 0.05%.
Bulk density, Method I 616 Using the procedure specified in the chapter, determine the bulk density of Magnesium Oxide.
Assay— Ignite about 500 mg of Magnesium Oxide to constant weight in a tared platinum crucible, weigh the residue accurately, dissolve it in 30.0 mL of 1 N sulfuric acid VS, add methyl orange TS, and titrate the excess acid with 1 N sodium hydroxide VS. Record the volume, VA, in mL, of 1 N sodium hydroxide consumed. Perform the blank determination, and record the volume, VB, in mL, of 1 N sodium hydroxide consumed. Calculate the volume, VS, of 1 N sulfuric acid, in mL, consumed by the sample, by the formula:
in which NNaOH is the exact normality of the sodium hydroxide solution. Calculate the volume of 1 N sulfuric acid, VCa, in mL, consumed by calcium that is present in the Magnesium Oxide taken for the Assay, by the formula:
(W × LCa) / (100 × 20.04)
in which W is the weight, in mg, of Magnesium Oxide taken; LCa is the content of calcium, in percentage, as determined in the test for Limit of calcium; and 20.04 is the weight, in mg, of Ca that is equivalent to each mL of 1 N sulfuric acid. Calculate the percentage of MgO in the portion of Magnesium Oxide taken by the formula:
100(VS VCa) × 20.15/W
in which 20.15 is the weight, in mg, of MgO that is equivalent to each mL of 1 N sulfuric acid; and the other terms are as defined above.
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Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Senior Scientist
(MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine
USP32–NF27 Page 2835
Pharmacopeial Forum: Volume No. 32(6) Page 1720
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.