Magaldrate
Aluminum magnesium hydroxide sulfate (Al5Mg10(OH)31(SO4)2·xH2O).

Aluminum magnesium hydroxide sulfate,hydrate [74978-16-8].

Anhydrous 1097.38
»Magaldrate is a chemical combination of aluminum and magnesium hydroxides and sulfate,corresponding approximately to the formula:
Al5Mg10(OH)31(SO4)2·xH2O.
It contains the equivalent of not less than 90.0percent and not more than 105.0percent of Al5Mg10(OH)31(SO4)2,calculated on the dried basis.
Packaging and storage— Preserve in well-closed containers.
Identification—
A: Dissolve about 600mg in 20mLof 3Nhydrochloric acid,add 3drops of methyl red TSand about 30mLof water,and heat to boiling.Add 6Nammonium hydroxide until the color just changes to yellow,continue boiling for 2minutes,and filter:the filtrate responds to the tests for Magnesium á191ñ.
B: Wash the precipitate obtained in Identificationtest Awith 50mLof hot ammonium chloride solution (1in 50),then dissolve the precipitate in 15mLof 3Nhydrochloric acid:the solution responds to the tests for Aluminum á191ñ.
C: Its X-ray diffraction pattern (see X-ray Diffraction á941ñ)in the d-spacings region below 0.257nm (2.57angstrom units)conforms to that of USP Magaldrate RS.
Microbial limits á61ñ— It meets the requirements of the test for absence of Escherichia coli.
Loss on drying á731ñ— Dry it at 200for 4hours:it loses between 10.0%and 20.0%of its weight.
Soluble chloride— Boil 1g of it,accurately weighed,with 50.0mLof water for 5minutes,cool,add water to restore the original volume,mix,and filter.To 25.0mLof the filtrate add 0.1mLof potassium chromate TS,and titrate with 0.10Nsilver nitrate until a persistent pink color is obtained:not more than 5.0mLof 0.10Nsilver nitrate is required (3.5%).
Soluble sulfate á221ñ— A2.5-mLportion of the filtrate obtained in the test for Soluble chlorideshows no more sulfate than corresponds to 1.0mLof 0.020Nsulfuric acid (1.9%).
Sodium— Transfer 2g of it,accurately weighed,to a 100-mLvolumetric flask,place in an ice bath,add 5mLof nitric acid,and swirl to dissolve.Allow to warm to room temperature,dilute with water to volume,and mix.Filter,if necessary,to obtain a clear solution.Dilute 10.0mLof the filtrate with water to 100.0mL:the emission intensity of this solution,determined with a suitable flame photometer at 589nm and corrected for background transmission at 580nm,is not greater than that produced by a standard containing 2.2µg of Na per mL,similarly measured (0.11%).
Heavy metals á231ñ— Dissolve 330mg in 10mLof 3Nhydrochloric acid,filter if necessary to obtain a clear solution,and dilute with water to 25mL:the limit is 0.006%.
Organic volatile impurities,Method Vá467ñ: meets the requirements.
Solvent— Use dimethyl sulfoxide.
Magnesium hydroxide content— Dissolve about 100mg,accurately weighed,in 3mLof dilute hydrochloric acid (1in 10),and dilute with water to about 200mL.Add,with stirring,1g of ammonium chloride,20mLof triethanolamine,10mLof ammonia–ammonium chloride buffer TS,and 0.1mLof eriochrome black TS,and titrate with 0.05Medetate disodium VSto a blue color.Perform a blank determination,and make any necessary correction.Each mLof 0.05Medetate disodium is equivalent to 2.916mg of Mg(OH)2:between 49.2%and 66.6%of Mg(OH)2is found,calculated on the dried basis.
Aluminum hydroxide content—
Edetate disodium titrant— Prepare and standardize as directed in the Assayunder Ammonium Alum.
Procedure— Dissolve about 100mg of Magaldrate,accurately weighed,in 3mLof dilute hydrochloric acid (1in 10),and dilute with water to about 30mL.Add,with stirring,25.0mLof Edetate disodium titrant,mix,and allow to stand for 5minutes.Then add 20mLof acetic acid-ammonium acetate buffer TS,60mLof alcohol,and 2mLof dithizone TS,and titrate with 0.05Mzinc sulfate to a bright rose-pink color.Perform a blank determination,and make any necessary correction.Each mLof 0.05MEdetate disodium titrantis equivalent to 3.900mg of Al(OH)3:between 32.1%and 45.9%of Al(OH)3is found,calculated on the dried basis.
Sulfate content—
Chromatographic column— Transfer 15mLof strongly acidic 50-to 100-mesh styrene-divinylbenzene cation-exchange resin to a 1-cm inside diameter glass column.Wash the resin with 30mLof water.
Indicator solution— Prepare a solution in water containing 2mg of sodium alizarinsulfonate per mL.
Magnesium acetate solution— Dissolve 26.8g of magnesium acetate in 500mLof water.
0.05M Barium chloride— Dissolve 12.2g of barium chloride in about 900mLof water,adjust with 1Nhydrochloric acid to a pHof 3.0,dilute with water to 1000mL,and mix.Standardize this solution as follows:Transfer 10.0mLof 0.1Nsulfuric acid VSto a 125-mLconical flask.Adjust by adding Magnesium acetate solutionto a pHof 3.0.Add 25mLof methanol and 3or 4drops of Indicator solution.Add from a buret an accurately measured volume of 8to 9mLof 0.05Mbarium chloride.Add an additional 4drops of Indicator solution,and titrate slowly until the yellow color disappears and a pink tinge is visible.Calculate the molarity of the barium chloride titrant taken by the formula:
5(N/V),
in whichNis the normality of the sulfuric acid;and Vis the volume,in mL,of titrant consumed.
Test preparation— Transfer about 875mg of Magaldrate,accurately weighed,to a 25-mLvolumetric flask.Dissolve in 10mLof water and 5mLof glacial acetic acid,dilute with water to volume,and mix.Transfer 5.0mLof this solution to the chromatographic column and wash the column with 15mLof water,collecting the eluate in a 125-mLconical flask (Test preparation).
Procedure— Add to the Test preparation5mLof Magnesium acetate solution,32mLof methanol,and 3or 4drops of Indicator solution.Add from a buret an accurately measured volume of 5.0to 5.5mLof 0.05Mbarium chloride.Add an additional 3drops of Indicator solution,and titrate slowly until the yellow color disappears and a pink tinge is visible.Each mLof 0.05Mbarium chloride is equivalent to 4.803mg of sulfate (SO4):between 16.0%and 21.0%of SO4is found,calculated on the dried basis.
Assay— Transfer about 3g of Magaldrate,accurately weighed,to a 250-mLbeaker,add 100.0mLof 1Nhydrochloric acid VS,and stir until the solution becomes clear.Titrate the excess acid with 1Nsodium hydroxide VSto a pHof 3.0,determined potentiometrically.Perform a blank determination (see Residual Titrationsunder Titrimetry á541ñ).Each mLof 1Nhydrochloric acid is equivalent to 35.40mg of Al5Mg10(OH)31(SO4)2.
Auxiliary Information— Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1162
Phone Number:1-301-816-8251