Magnesium Chloride
(mag nee' zee um klor' ide).

MgCl2·6H2O 203.30
Magnesium chloride, hexahydrate     [7791-18-6].
Anhydrous     95.21 [7786-30-3].
DEFINITION
Magnesium Chloride contains NLT 98.0% and NMT 101.0% of MgCl2·6H2O.
IDENTIFICATION
•  A. Identification Tests—General, Magnesium 191
Sample solution:  50 mg/mL
•  B. Identification Tests—General, Chloride 191
Sample solution:  50 mg/mL
[Note—Acidify the Sample solution with diluted nitric acid before adding 6 N ammonium hydroxide. ]
ASSAY
•  Procedure
Sample:  450 mg
Analysis:  Dissolve the Sample in 25 mL of water, add 5 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. Each mL of 0.05 M disodium edetate is equivalent to 10.17 mg of MgCl2·6H2O.
Acceptance criteria:  98.0%–101.0%
IMPURITIES
•  Insoluble Matter
Sample:  20 g
Analysis:  Dissolve the Sample in 200 mL of water, heat to boiling, and digest in a covered beaker on a steam bath for 1 h. Filter through a tared filtering crucible, wash thoroughly, dry at 115, and determine the weight of the residue.
Acceptance criteria:  NMT 0.005%
•  Chloride and Sulfate, Sulfate 221
Sample:  10 g
Acceptance criteria:  It shows no more sulfate than corresponds to 0.50 mL of 0.020 N sulfuric acid (0.005%).
•  Barium
Sample:  1 g
Analysis:  Dissolve the Sample in 10 mL of water, and add 1 mL of 2 N sulfuric acid.
Acceptance criteria:  No turbidity is produced within 2 h.
•  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:  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.
Standard solutions:  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. Transfer 1.0, 5.0, 10.0, and 15.0 mL of this stock solution to separate 1000-mL volumetric flasks, each containing 20 mL of Lanthanum solution and 40 mL of Dilute hydrochloric acid. Dilute with water to volume. These Standard solutions contain 1.0, 5.0, 10.0, and 15.0 µg/mL of calcium, respectively.
Blank solution:  Transfer 4 mL of Lanthanum solution and 10 mL of Dilute hydrochloric acid to a 200-mL volumetric flask, and dilute with water to volume.
Sample solution:  Transfer 10.0 g of Magnesium Chloride to a 200-mL volumetric flask, and add water to dissolve. Add 4 mL of Lanthanum solution, and dilute with water to volume.
Instrumental conditions 
Mode:  Atomic absorption spectrophotometry
Lamp:  Calcium hollow-cathode
Flame:  Nitrous oxide–acetylene
Analytical wavelength:  Calcium emission line at 422.7 nm
Analysis 
Samples:  Standard solutions, Blank solution, and Sample solution.
Determine the concentration, C, in µg/mL, of calcium in the Sample solution using the calibration graph.
Calculate the percentage of calcium in the portion of Magnesium Chloride taken:
Result = (V/W × C × F) × 100
V== volume of the Sample solution (mL)
W== weight of Magnesium Chloride taken (mg)
C== as defined above
F== conversion factor from µg/mL to mg/mL, 0.001
Acceptance criteria:  NMT 0.01%
•  Potassium
Sample solution:  5 g
Analysis:  Dissolve the Sample in 5 mL of water, and add 0.2 mL of sodium bitartrate TS.
Acceptance criteria:  No turbidity is produced within 5 min.
•  Aluminum 206 (where it is labeled as intended for use in hemodialysis)
Test preparation:  Prepare as directed in the chapter, using 2.0 g.
Acceptance criteria:  NMT 1 ppm
•  Heavy Metals 231
Test preparation:  Dissolve 2 g in water, and dilute with water to 25 mL.
Acceptance criteria:  NMT 10 ppm
SPECIFIC TESTS
•  pH 791
Sample solution:  50 mg/mL in carbon dioxide-free water
Acceptance criteria:  4.5–7.0
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight containers.
•  Labeling: Where Magnesium Chloride is intended for use in hemodialysis, it is so labeled.
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
1-301-816-8251
(SM32010) Monographs - Small Molecules 3
USP35–NF30 Page 3744
Pharmacopeial Forum: Volume No. 32(6) Page 1720