A: Place about 1g in a flask equipped with a stopper and glass tubing,the tip of which is immersed in calcium hydroxide TSin a test tube.Add 5mLof 3Nhydrochloric acid to the flask,and immediately insert the stopper:gas evolves in the flask and a precipitate is formed in the test tube.

B: To a solution of 5g in 10mLof 3Nhydrochloric acid add 5drops of methyl red TS,heat to boiling,add 6Nammonium hydroxide until the color of the solution changes to deep yellow,then continue boiling for 2minutes,and filter:the filtrate responds to the tests forMagnesium á191ñ.

C: Wash the precipitate obtained inIdentification testBwith a hot solution of ammonium chloride (1in 50),and dissolve the precipitate in hydrochloric acid:the solution responds to the tests forAluminum á191ñ.

0.55(0.0385A)+0.8(0.024M),

Potassium chloride solution— Prepare a solution containing 4.5g of potassium chloride in each 100mL.

Aluminum stock solution— Transfer 1.000g of aluminum wire to a 1000-mLvolumetric flask,and add 50mLof 6Nhydrochloric acid.Swirl to ensure contact of the aluminum and the acid,and allow the reaction to proceed until all of the aluminum has dissolved.Dilute with water to volume,and mix.

Standard preparations— To separate 100-mLvolumetric flasks,each containing 10mLofPotassium chloride solution,transfer 9.0,10.0,and 11.0mL,respectively,ofAluminum stock solution,dilute with water to volume,and mix.TheseStandard preparationscontain 90.0,100.0,and 110.0µg of aluminum per mL,respectively.

Assay preparation— Transfer an accurately measured quantity of Oral Suspension,previously shaken in its original container,equivalent to about 75mg of aluminum hydroxide,to a suitable beaker.Add 25mLof 6Nhydrochloric acid,and heat on a steam bath for 30minutes,with occasional swirling.Cool,and transfer with the aid of water to a 250-mLvolumetric flask containing 25mLofPotassium chloride solution.Dilute with water to volume,mix,and filter.

Procedure— Concomitantly determine the absorbances of theStandard preparationsand theAssay preparationat the aluminum emission line at 309.3nm,with a suitable atomic absorption spectrophotometer (seeSpectrophotometry and Light-Scattering á851ñ)equipped with an aluminum hollow-cathode lamp and a nitrous oxide–acetylene flame,using water as the blank.Calculate the quantity,in mg,of Al(OH)3in the portion of Oral Suspension taken by the formula: in which 78.00is the molecular weight of aluminum hydroxide;26.98is the atomic weight of aluminum;AUis the absorbance of theAssay preparation;and RSis the average of the ratios of the absorbances of theStandard preparationsto their respective concentrations,in µg of aluminum per mL.

Lanthanum chloride solution— Prepare a solution of lanthanum chloride in water containing 5mg per mL.

Magnesium stock solution— Transfer 1.000g of magnesium metal to a 1000-mLvolumetric flask containing 50mLof water,and slowly add 10mLof hydrochloric acid.Dilute with water to volume,and mix.Transfer 10.0mLof this solution to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Standard preparations— To separate 100-mLvolumetric flasks,each containing 10mLof Lanthanum chloride solution,transfer 1.70mLand 1.80mL,respectively,ofMagnesium stock solution,dilute with water to volume,and mix.These Standard preparationscontain 1.7µg of magnesium per mLand 1.8µg of magnesium per mL,respectively.

Assay preparation— Quantitatively dilute an accurately measured volume of theAssay preparationprepared as directed in theAssay for aluminum hydroxidewith water to obtain a solution having a concentration of about 6µg of magnesium carbonate per mL.

Procedure— Concomitantly determine the absorbances of theStandard preparationsand theAssay preparationat the magnesium emission line at 285.2nm,with a suitable atomic absorption spectrophotometer (seeSpectrophotometry and Light-Scattering á851ñ)equipped with a magnesium hollow-cathode lamp and an air–acetylene flame,using water as the blank.Calculate the quantity,in mg,of magnesium carbonate (MgCO3)in the portion of Oral Suspension taken by the formula: in which 84.31is the molecular weight of magnesium carbonate;24.31is the atomic weight of magnesium;Lis the labeled quantity,in mg,of magnesium carbonate in the portion of Oral Suspension taken;Dis the concentration,in µg of magnesium carbonate per mL,of theAssay preparation,based on the labeled amount of magnesium carbonate in the portion of Oral Suspension taken and the extent of dilution;AUis the absorbance of theAssay preparation;and RSis the average of the ratios of the absorbances of theStandard preparationsto their respective concentrations,in µg of magnesium per mL.