»Magnesium Aluminometasilicate is a synthetic material that exists in two forms,Type I-Aand Type I-B,having different pHrequirements.The required contents for both forms are the same:not less than 29.1percent and not more than 35.5percent of aluminum oxide (Al2O3),not less than 11.4percent and not more than 14.0percent of magnesium oxide (MgO),and not less than 29.2percent and not more than 35.6percent of silicon dioxide (SiO2),calculated on the dried basis.
Packaging and storage Preserve in tight containers,and prevent exposure to excessive heat.
Labeling Label it to indicate whether it is Type I-Aor Type I-B.
A: Transfer 0.5g of Magnesium Aluminometasilicate to a suitable container,add 5mLof a sulfuric acid solution (1in 3),and heat until white fumes are observed.Cool,add 20mLof water,and filter.Neutralize the filtrate with ammonia TS,and retain for use in Identificationtest B.Collect the precipitate,and dissolve in 3Nhydrochloric acid:the solution meets the requirements of the tests for Aluminum á191ñ.
B: The filtrate retained from Identificationtest Ameets the requirements of the tests for Magnesium á191ñ.
C: Prepare a bead by fusing a few crystals of sodium ammonium phosphate on a platinum loop in the flame of a Bunsen burner.Place the hot,transparent bead in contact with Magnesium Aluminometasilicate,and again fuse:silica floats about in the bead producing,upon cooling,an opaque bead with a web-like structure.
Acid-consuming capacity Transfer about 0.2g of Magnesium Aluminometasilicate,accurately weighed,to a glass-stoppered flask,and add 100.0mLof 0.1Nhydrochloric acid VS.Stopper the flask tightly,shake at 37±2for 1hour,and filter.Transfer 50.0mLof the filtrate to a beaker,and while stirring,titrate the excess hydrochloric acid with 0.1Nsodium hydroxide VSto attain a pHof 3.5.Perform a blank determination,and make any necessary correction.Not less than 210mLof 0.1Nhydrochloric acid is consumed per g of Magnesium Aluminometasilicate,calculated on the dried basis.
pHá791ñ Transfer 2g of Magnesium Aluminometasilicate to a suitable container,and add 50mLof water.While stirring,immerse the pHelectrodes in the suspension,and after 2minutes,record the pH:between 6.5and 8.5for Type I-A,and between 8.5and 10.5for Type I-B.
Loss on drying á731ñ Dry it at 110for 7hours:it loses not more than 20.0%of its weight.
Soluble salts Transfer 10.0g of Magnesium Aluminometasilicate to a suitable container,add 150mLof water,and boil gently for 15minutes,with shaking.After cooling,dilute with water to 150mL,and centrifuge.Dilute 75mLof the clear filtrate with water to 100mL,and retain the diluted filtrate for use in the tests for Alkalinity,Chloride,and Sulfate.Evaporate 25mLof the diluted filtrate on a water bath,and heat at 700for 2hours.The residue weighs not more than 0.020g:not more than 1.6%is found.
Alkalinity Add 2drops of phenolphthalein TSto 20mLof the diluted filtrate retained from the test for Soluble salts,containing 1g of Magnesium Aluminometasilicate:if a pink color is produced,not more than 0.50mLof 0.1Nhydrochloric acid is required to discharge it.
Chloride á221ñ A20-mLportion of the diluted filtrate retained from the test for Soluble saltsshows no more chloride than corresponds to 0.75mLof 0.020Nhydrochloric acid:not more than 0.053%is found.
Sulfate á221ñ A2-mLportion of the diluted filtrate retained from the test for Soluble saltsshows no more sulfate than corresponds to 0.5mLof 0.020Nsulfuric acid:not more than 0.480%is found.
Arsenic,Method Iá211ñ: 3µg per g.
Test Preparation To 0.11g of Magnesium Aluminometasilicate add 8mLof 2Nnitric acid,boil for 1minute,and cool.Dilute with water to 100mL,and centrifuge.Dilute 30mLof the supernatant with water to 45mL:the limit is 0.03%.
Heavy metals,Method Iá231ñ
Test Preparation Transfer 2.67g of Magnesium Aluminometasilicate to a suitable container,add 20mLof water and 8mLof hydrochloric acid,and evaporate to dryness on a water bath.To the residue add 5mLof 1Nacetic acid and 20mLof water,boil for 2minutes,add 0.4g of hydroxylamine hydrochloride,and heat to boiling.Cool,dilute with water to 100mL,and filter.Use 25mLof the filtrate as the Test Preparation.
Monitor Preparation Transfer another 25mLof the diluted filtrate to a suitable container,and add 2.0mLof Standard Lead Solution.
Standard Preparation Transfer 2mLof hydrochloric acid to a suitable container,and evaporate to dryness on a water bath.To the residue add 2.0mLof Standard Lead Solutionand 0.1g of hydroxylamine hydrochloride.Dilute with water to 25mL:the limit is 30µg per g.
Assay for aluminum oxide
Edetate disodium titrant Prepare and standardize as directed in the Assayunder Ammonium Alum.
Assay preparation Transfer about 1.25g of Magnesium Aluminometasilicate,accurately weighed,to a conical flask,add 10mLof 3Nhydrochloric acid and 50mLof water,and heat on a water bath for 15minutes.To this solution add 8mLof hydrochloric acid,and heat on a water bath for 10minutes.After cooling,transfer the solution to a 250-mLvolumetric flask,rinse the conical flask with water,and add the washings to the volumetric flask.Dilute with water to volume,and mix.Centrifuge,and use the supernatant as the Assay preparation.Retain a portion of the Assay preparationfor use in the Assay for magnesium oxide.
Procedure Transfer 20.0mLof the Assay preparationto a beaker,and add 20.0mLof Edetate disodium titrant.To this solution add 15mLof acetic acidammonium acetate buffer TSand 20mLof water,and boil for 5minutes.After cooling,add 50mLof alcohol and 2mLof dithizone TS,and titrate with 0.05Mzinc sulfate VSuntil the color of the solution changes from green-violet to rose-pink.Perform a blank determination,and make any necessary correction.Each mLof 0.05MEdetate disodium titrantis equivalent to 2.5490mg of Al2O3.
Assay for magnesium oxide Transfer 50.0mLof the Assay preparationretained from the Assay for aluminum oxideto a suitable container,add 50mLof water and 25mLof a trolamine solution (1in 2),and shake well.Add 25mLof ammoniaammonium chloride buffer TSand 0.04g of eriochrome black TStrituration as the indicator.Titrate with 0.05Medetate disodium VSuntil the red-purple color changes to blue and persists for 30seconds.Each mLof 0.05Medetate disodium VSis equivalent to 2.0152mg of MgO.
Assay for silicon dioxide Transfer about 1g of Magnesium Aluminometasilicate,accurately weighed,to a suitable container,add 30mLof 3Nhydrochloric acid,and evaporate on a water bath to dryness.Moisten the residue with hydrochloric acid,and again evaporate on a water bath to dryness.To the residue add 8mLof hydrochloric acid and 25mLof hot water,and stir.Allow to stand,and then decant the supernatant through an ashless filter paper.To the residue in the container add 10mLof hot water,stir,and decant the supernatant through the filter paper.Wash the residue in the container with three additional 10-mLportions of hot water,stir,and decant as described above.Treat the residue in the container with 50mLof water,and heat on a water bath for 15minutes.Filter,and rinse the residue on the filter paper with hot water until no precipitate is obtained when 1mLof silver nitrate TSis added to 5mLof the washing.Transfer the filter paper and its contents to a tared platinum crucible,heat to dryness,incinerate,and continue to heat at 800±25for 1hour.Cool,and weigh.Moisten the residue with 6mLof hydrofluoric acid,evaporate to dryness,and ignite for 5minutes.Cool,and weigh.The loss in weight represents the weight of silicon dioxide (SiO2).
Auxiliary Information Staff Liaison:Catherine Sheehan,B.Sc.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28NF23Page 3026Pharmacopeial Forum:Volume No.28(4)Page 1214