Magnesium Carbonate
Carbonic acid,magnesium salt,basic;or,Carbonic acid,magnesium salt (1:1),hydrate
Magnesium carbonate,basic;or,Magnesium carbonate (1:1)hydrate [23389-33-5].
Anhydrous 84.31 [546-93-0].
»Magnesium Carbonate is a basic hydrated magnesium carbonate or a normal hydrated magnesium carbonate.It contains the equivalent of not less than 40.0percent and not more than 43.5percent of magnesium oxide (MgO).
Packaging and storage—
Preserve in well-closed containers.
Identification—
When treated with 3Nhydrochloric acid,it dissolves with effervescence,and the resulting solution responds to the tests for Magnesium á191ñ.
Microbial limits á61ñ—
It meets the requirements of the test for absence of Escherichia coli.
Soluble salts—
Mix 2.0g with 100mLof a mixture of equal volumes of n-propyl alcohol and water.Heat the mixture to the boiling point with constant stirring,cool to room temperature,dilute with water to 100mL,and filter.Evaporate 50mLof the filtrate on a steam bath to dryness,and dry at 105
for 1hour:the weight of the residue does not exceed 10mg (1.0%).
for 1hour:the weight of the residue does not exceed 10mg (1.0%).
Acid-insoluble substances—
Mix 5.0g with 75mLof water,add hydrochloric acid in small portions,with agitation,until no more of the magnesium carbonate 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 2.5mg (0.05%).
Arsenic,Method Iá211ñ—
Prepare the Test Preparationby dissolving 750mg in 25mLof 3Nhydrochloric acid.The limit is 4ppm.
Limit of calcium—
Dilute hydrochloric acid—
Dilute 100mLof hydrochloric acid with water to 1000mL.
Lanthanum solution—
To 58.65g of lanthanum oxide add 400mLof water,and add,gradually with stirring,250mLof hydrochloric acid.Stir until dissolved,dilute with water to 1000mL,and mix.
Standard preparations—
Transfer 249.7mg of calcium carbonate,previously dried at 300for 3hours and cooled in a desiccator for 2hours,to a 100-mLvolumetric flask,dissolve in a minimum amount of hydrochloric acid,dilute with water to volume,and mix.Transfer 5.0,10.0,and 15.0mLof this stock solution to separate 1000-mLvolumetric flasks,each containing 20mLof Lanthanum solutionand 40mLof Dilute hydrochloric acid,add water to volume,and mix.These Standard preparationscontain 5.0,10.0,and 15.0µg of calcium in each mL,respectively.
for 3hours and cooled in a desiccator for 2hours,to a 100-mLvolumetric flask,dissolve in a minimum amount of hydrochloric acid,dilute with water to volume,and mix.Transfer 5.0,10.0,and 15.0mLof this stock solution to separate 1000-mLvolumetric flasks,each containing 20mLof Lanthanum solutionand 40mLof Dilute hydrochloric acid,add water to volume,and mix.These Standard preparationscontain 5.0,10.0,and 15.0µg of calcium in each mL,respectively.
Blank solution—
Transfer 4mLof Lanthanum solutionand 10mLof Dilute hydrochloric acidto a 200-mLvolumetric flask,dilute with water to volume,and mix.
Test preparation—
Transfer 250mg of Magnesium Carbonate to a beaker,add 30mLof Dilute hydrochloric acid,and stir until dissolved,heating if necessary.Transfer the solution so obtained to a 200-mLvolumetric flask containing 4mLof Lanthanum solution,dilute with water to volume,and mix.
Procedure—
Concomitantly determine the absorbances of the Standard preparationsand the Test preparationat the calcium emission line at 422.7nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with a calcium hollow-cathode lamp and an air–acetylene flame,using the Blank solutionas the blank.Plot the absorbances of the Standard preparationsversus their concentrations of calcium,in µg per mL,and draw a straight line through the three points.From the line so obtained and the absorbance of the Test preparation,determine the concentration,in µg per mL,of calcium in the Test preparation.Calculate the percentage of calcium in the specimen by multiplying this value by 0.08:the limit is 0.45%.
Heavy metals,Method Iá231ñ—
Dissolve 0.67g in 10mLof 3Nhydrochloric acid in a suitable crucible,and evaporate the solution on a steam bath to dryness.Ignite at 550±25until all carbonaceous material is consumed.Dissolve the residue in 15mLof water and 5mLof hydrochloric acid,and evaporate 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 in the same manner as before to dryness.Redissolve the residue in 20mLof water,filter,if necessary,and add to the filtrate 2mLof 1Nacetic acid and water to make 25mL:the limit is 0.003%.
until all carbonaceous material is consumed.Dissolve the residue in 15mLof water and 5mLof hydrochloric acid,and evaporate 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 in the same manner as before to dryness.Redissolve the residue in 20mLof water,filter,if necessary,and add to the filtrate 2mLof 1Nacetic acid and water to make 25mL:the limit is 0.003%.
Iron á241ñ—
Boil 50mg with 5mLof 2Nnitric acid for 1minute.Cool,dilute with water to 45mL,add 2mLof hydrochloric acid,and mix:the limit is 0.02%.
Assay—
Dissolve about 1g of Magnesium Carbonate,accurately weighed,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 weight of Magnesium Carbonate taken for the assay.The difference is the volume of 1Nsulfuric acid equivalent to the magnesium oxide present.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 1166
Phone Number:1-301-816-8251