Magnesium Citrate Oral Solution
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C12H10Mg3O14 451.11

1,2,3-Propanetricarboxylic acid, hydroxy-, magnesium salt (2:3).
Magnesium citrate (3:2) [3344-18-1].
» Magnesium Citrate Oral Solution is a sterilized or pasteurized solution containing, in each 100 mL, not less than 7.59 g of anhydrous citric acid (C6H8O7) and an amount of magnesium citrate equivalent to not less than 1.55 g and not more than 1.9 g of magnesium oxide (MgO).
Magnesium Citrate Oral Solution may be prepared as follows:
Magnesium Carbonate 15 g
Anhydrous Citric Acid 27.4 g
Syrup 60 mL
Talc 5 g
Lemon Oil 0.1 mL
Potassium Bicarbonate 2.5 g
Purified Water, a sufficient quantity, to make 350 mL
Dissolve the anhydrous Citric Acid in 150 mL of hot Purified Water in a suitable dish, slowly add the Magnesium Carbonate, previously mixed with 100 mL of Purified Water, and stir until it is dissolved. Then add the Syrup, heat the mixed liquids to the boiling point, immediately add the Lemon Oil, previously triturated with the Talc, and filter the mixture, while hot, into a strong bottle (previously rinsed with boiling Purified Water) of suitable capacity. Add boiled Purified Water to make the product measure 350 mL. Use Purified Cotton as a stopper for the bottle, allow to cool, add the Potassium Bicarbonate, and immediately insert the stopper in the bottle securely. Finally, shake the solution occasionally until the Potassium Bicarbonate is dissolved, cap the bottle, and sterilize or pasteurize the solution.
note—An amount (30 g) of citric acid containing 1 molecule of water of hydration, equivalent to 27.4 g of anhydrous citric acid, may be used in the foregoing formula. In this process the 2.5 g of potassium bicarbonate may be replaced by 2.1 g of sodium bicarbonate, preferably in tablet form. The Oral Solution may be further carbonated by the use of carbon dioxide under pressure.
Packaging and storage— Preserve at controlled room temperature or in a cool place, in bottles containing not less than 200 mL.
(Official January 1, 2009)
A: It responds to the tests for Magnesium 191.
B: To 5 mL of Oral Solution add 1 mL of potassium permanganate TS and 5 mL of mercuric sulfate TS, and heat the solution: a white precipitate is formed.
Chloride 221 A 2.0-mL portion shows no more chloride than corresponds to 0.30 mL of 0.020 N hydrochloric acid (0.01%).
Sulfate 221 A 2.0-mL portion shows no more sulfate than corresponds to 0.30 mL of 0.020 N sulfuric acid (0.015%).
Tartaric acid— To 10 mL in a test tube add 1 mL of glacial acetic acid and 3 mL of a solution of potassium acetate (1 in 2), shake the mixture vigorously, then gently rub the inner wall of the test tube with a glass rod for a few minutes, and allow to stand for 1 hour: no white, crystalline precipitate soluble in 6 N ammonium hydroxide is formed.
Assay for anhydrous citric acid— Measure accurately 10 mL of Oral Solution, which previously has been freed from excessive carbon dioxide by repeated pouring, into a 250-mL beaker, and add 30 mL of water. Then add phenolphthalein TS and just enough 1 N sodium hydroxide to give the liquid a persistent pink color, and acidify with 4 drops of 1 N hydrochloric acid. Add 20 mL of calcium chloride TS, and concentrate, by boiling, to about 30 mL, stirring constantly with a rubber-tipped glass rod during the boiling. Completely transfer the precipitate from the hot mixture to a filter from 9 to 11 cm in diameter with the aid of small quantities of boiling water, then wash the precipitate five times with boiling water. Collect the filtrate and washings in a 150-mL beaker, and concentrate the solution, by boiling, to about 20 mL. Add sufficient 6 N ammonium hydroxide, dropwise, to give the liquid a distinct red color, and then concentrate to about 10 mL. Transfer the precipitate completely from the hot mixture to a filter from 7 to 9 cm in diameter with the aid of small quantities of boiling water, and wash the precipitate six times with 5-mL portions of boiling water.
Dry the two filters with the precipitates, and incinerate them together in a loosely covered platinum crucible, heating first at a low temperature until the precipitates are well charred, and then removing the cover and raising the temperature until the residue is nearly white. If a gas flame is used, prevent its contact with the mass in the crucible. Cool, place the crucible with its contents in a suitable beaker, and add about 30 mL of water and then 50.0 mL of 0.5 N hydrochloric acid VS. When the residue has dissolved, remove the crucible, rinsing it well with water into the beaker. Add 100 mL of water, cover the beaker with a watch glass, and boil gently for 10 minutes. Cool, and titrate the excess acid with 0.5 N sodium hydroxide VS, using phenolphthalein TS as the indicator. Each mL of 0.5000 N hydrochloric acid is equivalent to 32.02 mg of C6H8O7.
(Official until January 1, 2009)
Assay for anhydrous citric acid—
Mobile Phase, Standard Preparation 1, and Chromatographic System— Proceed as directed under Assay for Citric Acid/Citrate and Phosphate 345.
Assay preparation— Measure accurately 10 mL of Oral Solution that previously has been freed from excessive carbon dioxide by repeated pouring, into a suitable volumetric flask, and proceed as directed for Assay Preparation for Citric Acid/Citrate Assay under Assay for Citric Acid/Citrate and Phosphate 345.
Procedure— Proceed as directed for Procedure under 345, and calculate the quantity, in mg, of anhydrous citric acid (C6H8O7) in the volume of Oral Solution taken by the formula:
0.001(192.12 / 189.10)CSD(rU / rS)
in which 192.12 is the molecular weight of anhydrous citric acid; 189.10 is the molecular weight of citrate (C6H5O7); CS is the concentration, in µg per mL, of citrate in Standard Preparation 1; D is the dilution factor; and rU and rS are the citrate peak areas obtained from the Assay preparation and Standard Preparation 1, respectively.
(Official January 1, 2009)
Assay for magnesium oxide— Transfer to a 100-mL volumetric flask 50.0 mL of Oral Solution that has been previously freed from excessive carbon dioxide by repeated pouring. Dilute with water to volume, and mix. Transfer 5.0 mL of this solution to a beaker containing 150 mL of water heated to 70 to 80, and add 1 mL of ammonium chloride TS and then 3 mL of ammonium hydroxide. Mix, and add slowly, with stirring, 8 mL of 8-hydroxyquinoline TS. After standing for 30 minutes, filter through a sintered-glass crucible, previously dried and weighed, and wash the precipitate with ten 10-mL portions of water. Dry the crucible and contents at 105 for 3 hours, cool, and weigh. Determine the equivalent of MgO in 100 mL of the Oral Solution by multiplying the weight of C18H12MgN2O2·2H2O so obtained by 4.624.
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