Magnesium Citrate
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1,2,3-Propanetricarboxylic acid,hydroxy-,magnesium salt (2:3).
Magnesium citrate (3:2) [3344-18-1].
»Magnesium Citrate contains not less than 14.5percent and not more than 16.4percent of magnesium (Mg),calculated on the dried basis.
Packaging and storage—
Preserve in tight containers.
Labeling—
Magnesium Citrate that loses not more than 2.0%of its weight in the test for Loss on dryingmay be labeled as Anhydrous Magnesium Citrate.
Identification—
A:
Asolution (10mg per mL)responds to the tests for Magnesium á191ñ.
B:
Asolution (80mg per mL)responds to the tests for Citrate á191ñ.
pHá791ñ:
between 5.0and 9.0,in a suspension (50mg per mL).
Loss on drying á731ñ—
Dry 1g in a mechanical convection oven at 135
for 16hours,then to constant weight:it loses not more than 29%of its weight,except that where it is labeled as anhydrous,it loses not more than 2.0%of its weight.
for 16hours,then to constant weight:it loses not more than 29%of its weight,except that where it is labeled as anhydrous,it loses not more than 2.0%of its weight.
Chloride á221ñ—
A300-mg portion shows no more chloride than corresponds to 0.20mLof 0.020Nhydrochloric acid (0.05%).
Sulfate á221ñ—
A100-mg portion shows no more sulfate than corresponds to 0.20mLof 0.020Nsulfuric acid (0.2%).
Arsenic,Method Iá211ñ:
3µg per g.
Heavy metals,Method Iá231ñ—
Dissolve 0.4g in 25mLof water,and proceed as directed for Test Preparation,except to use glacial acetic acid to adjust the pH:the limit is 50µg per g.
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 200µg per g.
Limit of calcium—
Dilute hydrochloric acid
,Lanthanum solution,Standard preparations,and Blank solution—Prepare as directed in the test for Calciumunder Magnesium Carbonate.
Test preparation—
Transfer 250mg of Magnesium Citrate to a beaker,add 30mLof Dilute hydrochloric acid,and stir until dissolved.Transfer the solution so obtained to a 200-mLvolumetric flask containing 4mLof Lanthanum solution,dilute with water to volume,and mix.
Procedure—
Proceed as directed in the test for Calciumunder Magnesium Carbonate:the limit is 1.0%,calculated on the dried basis.
Organic volatile impurities,Method IVá467ñ:
meets the requirements.
Assay—
Weigh accurately about 400mg of Magnesium Citrate,dissolve in 50mLof water,add 20mLof ammonia–ammonium chloride buffer TSand 0.1mLof eriochrome black TS,and titrate with 0.05Medetate disodium VSto a blue endpoint.Perform a blank determination,and make any necessary correction.From the volume of 0.05Medetate disodium consumed,deduct the volume of 0.05Medetate disodium corresponding to the amount of calcium in the portion of Magnesium Citrate taken,based on the amount of calcium found in the test for Limit of calcium.Each mg of calcium (Ca)is equivalent to 0.25mLof 0.05Medetate disodium.The difference is the volume of 0.05Medetate disodium consumed by the magnesium.Each mLof 0.05Medetate disodium is equivalent to 1.215mg of magnesium (Mg).
Auxiliary Information—
Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1169
Phone Number:1-301-816-8251