Magnesium Oxide
MgO 40.30

Magnesium oxide.
Magnesium oxide [1309-48-4].
»Magnesium Oxide,after ignition,contains not less than 96.0percent and not more than 100.5percent of MgO.
Packaging and storage— Preserve in tight containers.
Labeling— Label it to indicate whether it is Light Magnesium Oxide or Heavy Magnesium Oxide.
Identification— Asolution in diluted hydrochloric acid meets the requirements of the tests forMagnesium á191ñ.
Loss on ignition á733ñ— Transfer to a tared platinum crucible about 500mg,weigh accurately,and ignite at 800±25to constant weight:it loses not more than 10.0%of its weight.
Free alkali and soluble salts— Boil 2.0g with 100mLof water for 5minutes in a covered beaker,and filter while hot.To 50mLof the cooled filtrate add methyl red TS,and titrate with 0.10Nsulfuric acid:not more than 2.0mLof the acid is consumed.Evaporate 25mLof the remaining filtrate to dryness,and dry at 105for 1hour:not more than 10mg of residue remains (2.0%).
Acid-insoluble substances— Mix 2g with 75mLof water,add hydrochloric acid in small portions,with agitation,until no more dissolves,and boil for 5minutes.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 2mg (0.1%).
Limit of calcium—
Dilute hydrochloric acid,Lanthanum solution,Standard preparations,and Blank solution— Prepare as directed in the test forLimit of calciumunderMagnesium Carbonate.
Test preparation— Transfer 250mg of Magnesium Oxide,freshly ignited,to a beaker,add 30mLofDilute hydrochloric acid,and stir until dissolved,heating if necessary.Transfer the solution so obtained to a 200-mLvolumetric flask containing 4mLofLanthanum solution,dilute with water to volume,and mix.
Procedure— Proceed as directed in the test forLimit of calciumunderMagnesium Carbonate:the limit is 1.1%.
Heavy metals á231ñ— Dissolve 2.0g in 35mLof 3Nhydrochloric 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 20mLof water,and evaporate to dryness in the same manner as before.Redissolve the residue in 20mLof water,filter if necessary,and dilute with water to 40mL.To 20mLadd water to make 25mL:the limit is 20µg per g.
Iron á241ñ— Boil 40mg with 5mLof 2Nnitric acid for 1minute.Cool,dilute with water to 50mL,and mix.Dilute 25mLof this solution with water to 45mL,and add 2mLof hydrochloric acid:the limit is 0.05%.
Assay— Ignite about 500mg of Magnesium Oxide to constant weight in a tared platinum crucible,weigh the residue accurately,dissolve it in 30.0mLof 1Nsulfuric acid VS,add methyl orange TS,and titrate the excess acid with 1Nsodium hydroxide VS.From the volume of 1Nsulfuric acid consumed,deduct the volume of 1Nsulfuric acid corresponding to the content of calcium in the Magnesium Oxide taken for the assay.The difference is the volume of 1Nsulfuric acid equivalent to the MgOin the portion of Magnesium Oxide taken.Each mLof 1Nsulfuric acid is equivalent to 20.15mg of MgOand to 20.04mg of Ca.
Auxiliary Information— Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1172
Pharmacopeial Forum:Volume No.29(4)Page 1047
Phone Number:1-301-816-8251