Magnesium Carbonate

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 is a basic hydrated magnesium carbonate or a normal hydrated magnesium carbonate. It contains the equivalent of NLT 40.0% and NMT 43.5% of magnesium oxide (MgO).

2 IDENTIFICATION

A. Identification Tests—General 〈191〉, Chemical Identification Tests, Magnesium Sample solution: When treated with 3 N hydrochloric acid, it dissolves with effervescence.

Acceptance criteria: Meets the requirements

B. Identification Tests—General 〈191〉, Chemical Identification Tests, Carbonate

Analysis: Proceed as directed in test A.

Acceptance criteria: Meets the requirements

3 ASSAY

Procedure

Sample: 1 g of Magnesium Carbonate

Titrimetric system

Mode: Residual titration

Titrant: 1 N sodium hydroxide VS

Endpoint detection: Visual

Analysis: Dissolve the Sample in 30.0 mL of 1 N sulfuric acid VS, add methyl orange TS, and titrate the excess acid with Titrant. Perform the blank determination. Calculate the volume, V_s, of 1 N sulfuric acid VS, in mL, consumed by the Sample:

Result = (V_B− V_A) × N_NaOH

V_B = volume of Titrant consumed by the blank determination (mL)

V_A = volume of Titrant consumed by the Sample (mL)

N_NaOH = actual normality of the sodium hydroxide solution

Calculate the volume of 1 N sulfuric acid VS, V_Ca, in mL, consumed by calcium, which is present in the portion of Magnesium Carbonate taken for the Assay:

Result = (W × L_Ca )/(F_Ca × 100)

W = weight of Magnesium Carbonate taken (mg)

L_Ca = content of calcium as determined in the test for Limit of Calcium (%)

F_Ca = weight of Ca that is equivalent to each mL of 1 N sulfuric acid VS, 20.04 mg

Calculate the percentage of magnesium oxide (MgO) in the portion of Magnesium Carbonate taken:

Result = (V_S − V_Ca) × F_MgO/W × 100

V_S = volume of 1 N sulfuric acid VS consumed by the Sample, as calculated above (mL)

V_Ca = volume of 1 N sulfuric acid VS consumed by calcium, as calculated above (mL)

F_MgO = weight of MgO that is equivalent to each mL of 1 N sulfuric acid VS, 20.15 mg

W = weight of Magnesium Carbonate taken (mg)

Acceptance criteria: 40.0%–43.5% of magnesium oxide (MgO)

4 IMPURITIES

Soluble Salts

Sample: 2.0 g of Magnesium Carbonate

Analysis: Mix the Sample with 100 mL of 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 100 mL, and filter. Evaporate 50 mL of the filtrate on a steam bath to dryness, and dry at 105° for 1 h.

Acceptance criteria: The weight of the residue does not exceed 10 mg (NMT 1.0%).

Acid-Insoluble Substances

Sample: 5.0 g of Magnesium Carbonate

Analysis: Mix the Sample with 75 mL of water, add hydrochloric acid in small portions, with agitation, until no more of the magnesium carbonate dissolves, and boil for 5 min. If an insoluble residue remains, filter, wash well with water until the last washing is free from chloride, and ignite.

Acceptance criteria: The weight of the ignited residue does not exceed 2.5 mg (NMT 0.05%).

Change to read:

Arsenic 〈211〉, Procedures, Procedure 1 (CN 1-Jun-2023)

Test preparation: 750 mg of Magnesium Carbonate in 25 mL of 3 N hydrochloric acid

Acceptance criteria: NMT 4 ppm

Limit of Calcium

[Note—A commercially available atomic absorption standard solution for calcium may be used where preparation of a calcium standard stock solution is described below. Concentrations of the Standard solutions and the Sample solution may be modified to fit the linear or working range of the instrument.]

Dilute hydrochloric acid: Dilute 100 mL of hydrochloric acid with water to 1000 mL.

Lanthanum solution: 50 mg/mL of lanthanum prepared as follows. To 58.65 g of lanthanum oxide add 400 mL of water, and add, gradually with stirring, 250 mL of hydrochloric acid. Stir until dissolved, and dilute with water to 1000 mL.

Blank solution: Transfer 4 mL of the Lanthanum solution and 10 mL of Dilute hydrochloric acid to a 200-mL volumetric flask, and dilute with water to volume.

Standard stock solution: 1.0 mg/mL of calcium prepared as follows. Transfer 249.7 mg of calcium carbonate, previously dried at 300° for 3 h and cooled in a desiccator for 2 h, to a 100-mL volumetric flask. Dissolve in a minimum amount of hydrochloric acid, and dilute with water to volume.

Standard solution 1: 1.0 μg/mL of calcium prepared as follows. Transfer 1.0 mL of Standard stock solution to a 1000-mL volumetric flask containing 20 mL of the Lanthanum solution and 40 mL of Dilute hydrochloric acid, and dilute with water to volume.

Standard solution 2: 5.0 μg/mL of calcium prepared as follows. Transfer 5.0 mL of Standard stock solution to a 1000-mL volumetric flask containing 20 mL of the Lanthanum solution and 40 mL of Dilute hydrochloric acid, and dilute with water to volume.

Standard solution 3: 10.0 μg/mL of calcium prepared as follows. Transfer 10.0 mL of Standard stock solution to a 1000-mL volumetric flask containing 20 mL of the Lanthanum solution and 40 mL of Dilute hydrochloric acid, and dilute with water to volume.

Standard solution 4: 15.0 μg/mL of calcium prepared as follows. Transfer 15.0 mL of Standard stock solution to a 1000-mL volumetric flask containing 20 mL of the Lanthanum solution and 40 mL of Dilute hydrochloric acid, and dilute with water to volume.

Sample solution: 1.25 mg/mL of Magnesium Carbonate prepared as follows. Transfer 250 mg of Magnesium Carbonate to a beaker, add 30mL of Dilute hydrochloric acid, and stir until dissolved, heating if necessary. Transfer the solution so obtained to a 200-mL volumetric flask containing 4 mL of Lanthanum solution, and dilute with water to volume.

Instrumental conditions

(See Atomic Absorption Spectroscopy 〈852〉.)

Mode: Atomic absorption spectrophotometry

Analytical wavelength: 422.7 nm

Lamp: Calcium hollow–cathode

Flame: Nitrous oxide–acetylene

Analysis

Samples: Blank solution, Standard solutions, and Sample solution

Using the Blank solution as blank, determine the concentration, C_S, in μg/mL, of calcium in the Sample solution using the calibration graph.

Calculate the percentage of calcium in the portion of Magnesium Carbonate taken:

Result = (C_S× F/C_U) × 100

C_S = concentration of calcium in the Sample solution determined (μg/mL)

F = unit conversion factor, 0.001 mg/μg

C_U = concentration of Magnesium Carbonate in the Sample solution (mg/mL)

Acceptance criteria: NMT 0.45%

Change to read:

Iron 〈241〉, Procedures, Procedure 1 (CN 1-Jun-2023)

Test preparation: Boil 50 mg of Magnesium Carbonate with 5 mL of 2 N nitric acid for 1 min. Cool, dilute with water to 45 mL, add 2 mL of hydrochloric acid, and mix.

Acceptance criteria: NMT 200 ppm

5 SPECIFIC TESTS

Microbial Enumeration Tests 〈61〉 and Tests for Specified Microorganisms 〈62〉: It meets the requirements of the test for absence of Escherichia coli.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.