Magnesium Oxide Capsules
Magnesium Oxide Capsules contain NLT 90.0% and NMT 110.0% of the labeled amount of magnesium oxide (MgO).
•  A. Identification Tests—General, Magnesium 191
Sample solution:  Transfer the contents of 1 Capsule to a beaker. Add 10 mL of 3 N hydrochloric acid and 5 drops of methyl red TS, and heat to boiling. Add 6 N ammonium hydroxide until the color of the solution changes to deep yellow, then continue boiling for 2 min, and filter. Use the filtrate.
Acceptance criteria:  Meet the requirements
•  Procedure
Eriochrome black indicator solution:  Dissolve 200 mg of eriochrome black T in a mixture of 15 mL of triethanolamine and 5 mL of dehydrated alcohol.
Sample solution:  Mix the contents of NLT 20 Capsules. Transfer a portion of the powder, equivalent to 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.
Analysis:  Transfer 20.0 mL of the Sample 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 Eriochrome black indicator solution. Cool the solution to 3–4 by immersion of the beaker in an ice bath. 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 Sample solution, and make any necessary correction (see Titrimetry 541). Each mL of 0.05 M edetate disodium consumed is equivalent to 2.015 mg of MgO.
Acceptance criteria:  90.0%–110.0%
•  Dissolution 711
Medium:  0.1 N hydrochloric acid; 900 mL
Apparatus 1:  100 rpm
Time:  45 min
Analysis:  Using atomic absorption spectrophotometry at a wavelength of 285.2 nm, determine the amount of MgO dissolved, 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:  NLT 75% (Q) of the labeled amount of MgO is dissolved.
•  Uniformity of Dosage Units 905: Meet the requirements
•  Acid-Neutralizing Capacity 301: NLT 5 mEq of acid is consumed by the minimum single dose recommended in the labeling, and NLT 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.
•  Packaging and Storage: Preserve in well-closed containers.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Principal Scientific Liaison
(SM32010) Monographs - Small Molecules 3
711 Margareth R.C. Marques, Ph.D.
Senior Scientific Liaison
(GCDF2010) General Chapters - Dosage Forms
USP35–NF30 Page 3752