Packaging and storage—
Preserve in tight containers.
Labeling—
Magnesium Citrate that loses not more than 2.0% of its weight in the test for
Loss on drying may be labeled as Anhydrous Magnesium Citrate.
Identification—
A:
A solution (10 mg per mL) responds to the tests for
Magnesium 
191
.
B:
A solution (80 mg per mL) responds to the tests for
Citrate 191.
pH 791:
between 5.0 and 9.0, in a suspension (50 mg per mL).
Loss on drying 731—
Dry 1 g in a mechanical convection oven at 135
for 16 hours, then to constant weight: it loses not more than 29% of its weight, except that where it is labeled as anhydrous, it loses not more than 2.0% of its weight.
Chloride 221—
A 300-mg portion shows no more chloride than corresponds to 0.20 mL of 0.020 N hydrochloric acid (0.05%).
Sulfate 221—
A 100-mg portion shows no more sulfate than corresponds to 0.20 mL of 0.020 N sulfuric acid (0.2%).
Heavy metals, Method I 231—
Dissolve 0.4 g in 25 mL of water, and proceed as directed for
Test Preparation, except to use glacial acetic acid to adjust the pH: the limit is 50 µg per g.
Iron 241—
Boil 50 mg with 5 mL of 2 N nitric acid for 1 minute. Cool, dilute with water to 45 mL, add 2 mL of hydrochloric acid, and mix: the limit is 200 µg per g.
Limit of calcium—
Dilute hydrochloric acid
,
Lanthanum solution,
Standard preparations, and
Blank solution—Prepare as directed in the test for
Calcium under
Magnesium Carbonate.
Test preparation—
Transfer 250 mg of Magnesium Citrate to a beaker, add 30 mL of Dilute hydrochloric acid, and stir until dissolved. Transfer the solution so obtained to a 200-mL volumetric flask containing 4 mL of Lanthanum solution, dilute with water to volume, and mix.
Procedure—
Proceed as directed in the test for
Calcium under
Magnesium Carbonate: the limit is 1.0%, calculated on the dried basis.
Organic volatile impurities, Method IV 467:
meets the requirements.
Assay—
Weigh accurately about 400 mg of Magnesium Citrate, dissolve in 50 mL of water, add 20 mL of ammonia–ammonium chloride buffer TS and 0.1 mL of
eriochrome black TS, and titrate with 0.05
M edetate disodium VS to a blue endpoint. Perform a blank determination, and make any necessary correction. From the volume of 0.05
M edetate disodium consumed, deduct the volume of 0.05
M edetate disodium corresponding to the amount of calcium in the portion of Magnesium Citrate taken, based on the amount of calcium found in the test for
Limit of calcium. Each mg of calcium (Ca) is equivalent to 0.25 mL of 0.05
M edetate disodium. The difference is the volume of 0.05
M edetate disodium consumed by the magnesium. Each mL of 0.05
M edetate disodium is equivalent to 1.215 mg of magnesium (Mg).
;)
