Magnesium Carbonate and Citric Acid for Oral Solution

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

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 NLT 90.0% and NMT 110.0% of the labeled amount of magnesium citrate (C₁₂H₁₀Mg₃O₁₄).

2 IDENTIFICATION

A. Identification Tests—General, Magnesium 〈191〉

Sample solution: Constitute as directed in the labeling.

Acceptance criteria: Meets the requirements

B. The retention time of the citrate peak of the Sample solution corresponds to that of Standard solution 1, as obtained in the test for Content of Anhydrous Citric Acid.

3 ASSAY

Procedure

Sample solution: Transfer a volume of constituted oral solution, equivalent to 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 10 min. Dilute with water to volume. Stir by mechanical means for 30 min.

Analysis: Transfer 10.0 mL of the Sample solution to a 250-mL beaker. Add 10 mL of ammonia–ammonium chloride buffer TS, 5 mL of triethanolamine, and 0.3 mL of eriochrome black TS. 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).

Acceptance criteria: 90.0%–110.0%

4 OTHER COMPONENTS

Content of Anhydrous Citric Acid

Mobile phase, Standard solution 1, Chromatographic system, and System suitability: Proceed as directed in Assay for Citric Acid/Citrate and Phosphate 〈345〉.

Sample solution: Transfer an appropriate volume of the constituted oral solution into a suitable volumetric flask, and proceed as directed for the Sample solution in Assay for Citric Acid/Citrate and Phosphate 〈345〉, Assay Preparation for Citric Acid/Citrate Assay.

Analysis

Samples: Standard solution 1 and Sample solution

Proceed as directed for Assay for Citric Acid/Citrate and Phosphate 〈345〉, Procedure.

Calculate the percentage of anhydrous citric acid (C₆H₈O₇) in relation to the labeled amount of magnesium citrate in the volume of constituted oral solution taken:

Result = (r_U/r_S) × (C_S/C_U) × (M_r1/M_r2) × 100

r_U = peak area of citrate from the Sample solution

r_S = peak area of citrate from Standard solution 1

C_S = concentration of citrate in Standard solution 1 (mg/mL)

C_U = nominal concentration of magnesium citrate in the Sample solution (mg/mL)

M_r1 = molecular weight of anhydrous citric acid, 192.12

M_r2 = molecular weight of citrate (C₆H5O₇), 189.10

Acceptance criteria: 76.6%–107.8% of the labeled amount of magnesium citrate

5 PERFORMANCE TESTS

Uniformity of Dosage Units 〈905〉: Meets the requirements

6 IMPURITIES

Chloride and Sulfate, Chloride 〈221〉

Sample solution: Constitute as directed in the labeling.

Acceptance criteria: A 2.0-mL portion of Sample solution shows no more chloride than corresponds to 0.30 mL of 0.020 N hydrochloric acid (NMT 0.01%).

Chloride and Sulfate, Sulfate 〈221〉

Sample solution: Constitute as directed in the labeling.

Acceptance criteria: A 2.0-mL portion of Sample solution shows no more sulfate than corresponds to 0.30 mL of 0.020 N sulfuric acid (NMT 0.015%).

Tartaric Acid

Sample solution: Constitute as directed in the labeling.

Analysis: To 10 mL of Sample solution in a test tube, add 1 mL of glacial acetic acid and 3 mL of a solution of potassium acetate (1 in 2).

Shake the mixture vigorously, then gently rub the inner wall of the test tube with a glass rod for a few min, and allow to stand for 1 h.

Acceptance criteria: No white, crystalline precipitate soluble in 6 N ammonium hydroxide is formed.

7 SPECIFIC TESTS

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.

8 ADDITIONAL REQUIREMENTS

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.