Magnesium Gluconate
(mag nee' zee um gloo' koe nate).
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C12H22MgO14 414.60

C12H22MgO14·2H2O 450.64
d-Gluconic acid, magnesium salt (2:1), hydrate;    
Magnesium d-gluconate (1:2) hydrate;    
Magnesium d-gluconate (1:2) dihydrate     [59625-89-7].
Anhydrous     [3632-91-5].
DEFINITION
Magnesium Gluconate contains NLT 98.0% and NMT 102.0% of anhydrous magnesium gluconate (C12H22MgO14), calculated on the anhydrous basis.
IDENTIFICATION
•  A. Identification Tests—General, Magnesium 191: A 100-mg/mL solution meets the requirements.
•  B. Thin-Layer Chromatography
Standard solution:  10 mg/mL of USP Potassium Gluconate RS
Sample solution:  10 mg/mL of Magnesium Gluconate, heating in a water bath at 60, if necessary, to dissolve
Chromatographic system 
Mode:  TLC
Adsorbent:  0.25-mm layer of chromatographic silica gel
Application volume:  5 µL
Developing solvent system:  Alcohol, ethyl acetate, ammonium hydroxide, and water (50:10:10:30)
Spray reagent:  Dissolve 2.5 g of ammonium molybdate in 50 mL of 2 N sulfuric acid in a 100-mL volumetric flask, add 1.0 g of ceric sulfate, swirl to dissolve, and dilute with 2 N sulfuric acid to volume.
Analysis 
Samples:  Standard solution and Sample solution
Develop the chromatogram until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the chamber, and dry at 110 for 20 min. Allow to cool, and spray with the Spray reagent. Heat the plate at 110 for about 10 min.
Acceptance criteria:  The principal spot of the Sample solution corresponds in color, size, and RF value to that of the Standard solution.
ASSAY
•  Procedure
Sample:  800 mg of Magnesium Gluconate
Blank:  20 mL of water
Titrimetric system 
Mode:  Direct titration
Titrant:  0.05 M edetate disodium VS
Endpoint detection:  Visual
Analysis:  Dissolve the Sample in 20 mL of water. Add 5 mL of ammonia–ammonium chloride buffer TS and 0.1 mL of eriochrome black TS. Titrate with Titrant to a blue endpoint. Perform the Blank determination.
Calculate the percentage of magnesium gluconate (C12H22MgO14) in the Sample taken:
Result = {[(VS VB) × M × F ]/W} × 100]
VS== Titrant volume consumed by the Sample (mL)
VB== Titrant volume consumed by the Blank (mL)
M== Titrant molarity (mM/mL)
F== equivalency factor, 414.6 mg/mM
W== Sample weight (mg)
Acceptance criteria:  98.0%–102.0% on the anhydrous basis
IMPURITIES
•  Chloride and Sulfate, Chloride 221
Standard solution:  0.7 mL of 0.020 N hydrochloric acid
Sample:  1.0 g
Acceptance criteria:  NMT 0.05%
•  Chloride and Sulfate, Sulfate 221
Standard solution:  1.0 mL of 0.020 N sulfuric acid
Sample:  2.0 g
Acceptance criteria:  NMT 0.05%
•  Heavy Metals 231
Test preparation:  1.0 g in 10 mL of water. Add 6 mL of 3 N hydrochloric acid, and dilute with water to 25 mL.
Acceptance criteria:  NMT 20 ppm
•  Reducing Substances
Sample:  1.0 g of Magnesium Gluconate
Blank:  10 mL of water
Titrimetric system 
Mode:  Residual titration
Titrant:  0.1 N iodine VS
Back titrant:  0.1 N sodium thiosulfate VS
Endpoint detection:  Visual
Analysis:  Transfer the Sample to a 250-mL conical flask, dissolve in 10 mL of water, and add 25 mL of alkaline cupric citrate TS. Cover the flask, boil gently for 5 min, accurately timed, and cool rapidly to room temperature. Add 25 mL of 0.6 N acetic acid, 10.0 mL of Titrant, and 10 mL of 3 N hydrochloric acid, and titrate with Back titrant, adding 3 mL of starch TS as the endpoint is approached. Perform the Blank determination.
Calculate the percentage of reducing substances (as dextrose) in the Sample taken:
Result = {[(VB VS) × N × F]/W} × 100
VB== Back titrant volume consumed by the Blank (mL)
VS== Back titrant volume consumed by the Sample (mL)
N== Back titrant normality (mEq/mL)
F== equivalency factor, 27 mg/mEq
W== Sample weight (mg)
Acceptance criteria:  NMT 1.0%
SPECIFIC TESTS
•  pH 791
Sample solution:  50 mg/mL
Acceptance criteria:  6.0–7.8
•  Water Determination, Method Ib 921
Test preparation:  Proceed as directed in the chapter. Allow 30 min for solubilization of Magnesium Gluconate and for the reaction to reach completion.
Blank:  Use the same volume of Reagent as that of the Test preparation but without the specimen.
Analysis 
Samples:  Test preparation and Blank
Calculate the water content, in mg, of the Magnesium Gluconate taken:
Result = F × (XB X) × R
XB= = volume of standardized Water–Methanol Solution required to neutralize the unconsumed Reagent in the Blank determination (mL)
The other terms are as defined in Water Determination, Method Ib 921.
Acceptance criteria:  3.0%–12.0%
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in well-closed containers.
•  USP Reference Standards 11
USP Potassium Gluconate RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Huy T. Dinh, M.S.
Scientific Liaison
1-301-816-8594
(DS2010) Monographs - Dietary Supplements
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 3748