Magnesium Oxide Capsules
» Magnesium Oxide Capsules contain not less than 90.0 percent and not more than 110.0 percent of the labeled amount of magnesium oxide (MgO).
Packaging and storage— Preserve in well-closed containers.
Identification— Transfer the contents of 1 Capsule to a beaker, add 10 mL of 3 N hydrochloric acid and 5 drops of methyl red TS, heat to boiling, add 6 N ammonium hydroxide until the color of the solution changes to deep yellow, then continue boiling for 2 minutes, and filter: the filtrate so obtained responds to the tests for Magnesium 191.
Dissolution 711
Medium: 0.1 N hydrochloric acid; 900 mL.
Apparatus 1: 100 rpm.
Time: 45 minutes.
Procedure— Determine the amount of MgO dissolved, employing atomic absorption spectrophotometry at a wavelength of about 285.2 nm using filtered portions of the solution under test, suitably diluted with Medium if necessary, in comparison with a Standard solution having a known concentration of magnesium in the same Medium.
Tolerances— Not less than 75% (Q) of the labeled amount of MgO is dissolved in 45 minutes.
Uniformity of dosage units 905: meet the requirements.
Acid-neutralizing capacity 301: not less than 5 mEq of acid is consumed by the minimum single dose recommended in the labeling, and not less than 85.0% of the expected mEq value calculated from the results of the Assay is obtained. Each mg of MgO has an expected acid-neutralizing capacity value of 0.0492 mEq.
Assay— Weigh accurately the contents of not fewer than 20 Capsules, and mix. Transfer an accurately weighed portion of the powder, equivalent to about 500 mg of magnesium oxide, to a beaker, add 20 mL of water, and slowly add 40 mL of 3 N hydrochloric acid, with mixing. Heat the mixture to boiling, cool, and filter into a 200-mL volumetric flask. Wash the beaker with water, adding the washings to the filter. Add water to volume, and mix. Transfer 20.0 mL of this solution to a 400-mL beaker, add 180 mL of water and 20 mL of triethanolamine, and stir. Add 10 mL of ammonia–ammonium chloride buffer TS and 3 drops of an eriochrome black indicator solution prepared by dissolving 200 mg of eriochrome black T in a mixture of 15 mL of triethanolamine and 5 mL of dehydrated alcohol, and mix. Cool the solution to between 3 and 4 by immersion of the beaker in an ice bath, then remove, and titrate with 0.05 M edetate disodium VS to a blue endpoint. Perform a blank determination, substituting 20 mL of water for the assay solution, and make any necessary correction. Each mL of 0.05 M edetate disodium consumed is equivalent to 2.015 mg of magnesium oxide (MgO).
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Senior Scientist
(MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine
711 Margareth R.C. Marques, Ph.D.
Senior Scientist
(BPC05) Biopharmaceutics05
USP32–NF27 Page 2836