Packaging and storage—
Preserve in tight containers.
Labeling—
The label contains directions for constitution of the powder and states the equivalent amount of magnesium citrate (C12H10Mg3O14) in a given volume of the Oral Solution obtained after constitution.
(Official January 1, 2009)
Microbial limits 
61
—
It meets the requirements of the test for absence of
Escherichia coli and
Salmonella species.
Content of anhydrous citric acid—
Cation-exchange column—
Mix 10 g of styrene-divinylbenzene cation-exchange resin with 50 mL of water in a beaker. Allow the resin to settle, and decant and discard the supernatant until a slurry of resin remains. Pour the slurry into a 15-mm × 30-cm glass chromatographic tube having a pledget of glass wool in the bottom and a stopcock, and allow to settle as a homogeneous bed. Place a pledget of glass wool on the top of the bed. Wash the resin bed with about 100 mL of water, closing the stopcock when the water level has just entered the glass wool pledget on the surface above the resin bed.
Test solution—
Transfer an accurately measured volume of the constituted Oral Solution, equivalent to about 9 g of anhydrous citric acid, to a 100-mL volumetric flask, dilute with water to volume, and mix.
Procedure—
Transfer 5.0 mL of the Test solution carefully onto the top of the resin bed in the cation-exchange column. Place a 250-mL volumetric flask below the column, open the stopcock, and allow to flow until the solution has entered the resin bed. Elute the column with 70 mL of water at a rate of about 5 mL per minute, collecting the eluate in a beaker. Boil the eluate for 1 minute, cool, and add 5 drops of phenolphthalein TS. Titrate with 0.1 N sodium hydroxide VS to a pink endpoint. Each mL of 0.1 N sodium hydroxide is equivalent to 6.404 mg of anhydrous citric acid (C6H8O7). The content of anhydrous citric acid is between 76.6% and 107.8% of the labeled amount of magnesium citrate.
(Official until January 1, 2009)
Change to read:
Content of anhydrous citric acid—
Assay preparation—
Transfer an accurately measured volume of the constituted Oral Solution, equivalent to about 9 g of anhydrous citric acid into a suitable volumetric flask, and proceed as directed for
Assay Preparation for Citric Acid/Citrate Assay under
Assay for Citric Acid/Citrate and Phosphate 345.
Procedure—
Proceed as directed for
Procedure under
345, and calculate the quantity, in mg, of anhydrous citric acid (C
6H
8O
7) in the volume of constituted Oral Solution taken by the formula:
0.001(192.12/189.10)CS D(rU / rS)
in which 192.12 is the molecular weight of anhydrous citric acid; 189.10 is the molecular weight of citrate (C
6H
5O
7);
CS is the concentration, in µg per mL, of citrate in
Standard Preparation 1; D is the dilution factor; and
rU and
rS are the citrate peak areas obtained from the
Assay preparation and
Standard Preparation 1, respectively. The content of anhydrous citric acid is between 76.6% and 107.8% of the labeled amount of magnesium citrate.
USP29
(Official January 1, 2009)
Change to read:
Other requirements—
Constitute Magnesium Carbonate and Citric Acid for Oral Solution as directed in the labeling:
USP29 it responds to the
Identification tests and meets the requirements for
Chloride, Sulfate, and
Tartaric acid under
Magnesium Citrate Oral Solution.
Assay—
Transfer an accurately measured volume of constituted Oral Solution, equivalent to about 18.7 g of magnesium citrate (C
12H
10Mg
3O
14), to a 1000-mL volumetric flask. Add 200 mL of 1 N hydrochloric acid, swirl, and allow to stand for about 10 minutes. Dilute with water to volume, and mix. Stir by mechanical means for about 30 minutes. Transfer 10.0 mL of this solution to a 250-mL beaker. Add 10 mL of ammonia–ammonium chloride buffer TS, 5 mL of triethanolamine, 0.3 mL of
eriochrome black TS, and titrate with 0.05 M edetate disodium VS until the last hint of violet disappears (blue endpoint). Each mL of 0.05 M edetate disodium is equivalent to 7.520 mg of magnesium citrate (C
12H
10Mg
3O
14).
Auxiliary Information—
Staff Liaison :
Elena Gonikberg, Ph.D., Scientist
Expert Committee : (MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine
USP29–NF24 Page 1293
Pharmacopeial Forum : Volume No. 31(2) Page 419
Phone Number : 1-301-816-8251
