Magnesium Carbonate and Citric Acid for Oral Solution
» Magnesium Carbonate and Citric Acid for Oral Solution contains a dry mixture of Magnesium Carbonate and Citric Acid that when constituted as directed in the labeling yields a solution that contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of magnesium citrate (C12H10Mg3O14).
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.
USP Reference standards 11
Microbial enumeration tests 61 and Tests for specified microorganisms 62 It meets the requirements of the test for absence of Escherichia coli and Salmonella species.
Uniformity of dosage units 905: meets the requirements.
Content of anhydrous citric acid
Mobile Phase, Standard Preparation 1, and Chromatographic System Proceed as directed under Assay for Citric Acid/Citrate and Phosphate 345.
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 (C6H8O7) 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 (C6H5O7); 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.
Other requirements Constitute Magnesium Carbonate and Citric Acid for Oral Solution as directed in the labeling: 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 (C12H10Mg3O14), 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 ammoniaammonium 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 (C12H10Mg3O14).
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USP35NF30 Page 3743Pharmacopeial Forum: Volume No. 31(2) Page 419