Aluminum Phosphate Gel

Phosphoric acid,aluminum salt (1:1).
Aluminum phosphate (1:1) [7784-30-7].
»Aluminum Phosphate Gel is a water suspension containing not less than 4.0percent and not more than 5.0percent (w/w)of aluminum phosphate (AlPO4).It may contain sodium benzoate,benzoic acid,or other suitable agent,in an amount not exceeding 0.5percent,as a preservative.
Packaging and storage— Preserve in tight containers.
Identification—
A: Asolution of it in hydrochloric acid meets the requirements of the tests for Aluminum á191ñ.
B: Asolution of it in 2Nnitric acid meets the requirements of the tests for Phosphate á191ñ.
pHá791ñ: between 6.0and 7.2.
Soluble phosphate— Filter 20g,and wash the residue with 30mLof water.Add to the filtrate 2mLof nitric acid,heat to 60,and add 20mLof ammonium molybdate TS.Heat at 50for 30minutes,filter,wash the precipitate with dilute nitric acid (1in 36),then wash with potassium nitrate solution (1in 100)until the last portion of the filtrate is not acid to litmus paper.Dissolve the precipitate in 50.0mLof 0.5Nsodium hydroxide VS,add phenolphthalein TS,and titrate the excess alkali with 0.5Nhydrochloric acid VS.Each mLof 0.5Nsodium hydroxide is equivalent to 2.065mg of PO4.The soluble phosphate,calculated as PO4,does not exceed 0.30%.
Sulfate á221ñ— Add 10mLof 3Nhydrochloric acid to 10g of Gel,and heat to boiling.Cool,dilute with water to 250mL,and filter,if necessary.A10-mLportion of the solution shows no more sulfate than corresponds to 0.20mLof 0.020Nsulfuric acid:not more than 0.05%is found.
Arsenic,Method Iá211ñ— Prepare theTest Preparation by dissolving 5.0g of Gel in the smallest necessary volume of 3Nhydrochloric acid.The limit is 0.6ppm.
Heavy metals,Method Iá231ñ— Proceed as directed in the chapter,except to make the following modifications.
Standard Preparation— Into a 50-mLcolor-comparison tube pipet 4.0mLofStandard Lead Solution,dilute with water to 25mL,adjust with 6Nammonium hydroxide to a pHbetween 1.9and 2.1,dilute with water to 40mL,and mix.
Test Preparation— Dissolve 8.0g in 5mLof 3Nhydrochloric acid,warming if necessary,dilute with water to 25mL,and adjust with 6Nammonium hydroxide to a pHbetween 1.9and 2.1.Transfer to a 50-mLcolor-comparison tube,dilute with water to 40mL,and mix.
Monitor Preparation— Into a 50-mLcolor-comparison tube place 25mLof theTest Preparation,add 4.0mLofStandard Lead Solution,adjust with 1Nacetic acid or 6Nammonium hydroxide to a pHbetween 1.9and 2.1,dilute with water to 40mL,and mix.
Procedure— Proceed as directed in the chapter,except to omit the addition of 2mLofpH3.5Acetate Buffer.Not more than 5µg per g is found.
Chloride— Transfer 25g to a beaker with the aid of about 50mLof water,add 5mLof nitric acid,mix,then add,with stirring,30.0mLof 0.1Nsilver nitrate VS.Warm on a steam bath for 30minutes,filter,and wash the precipitate with water acidified with nitric acid.To the filtrate add ferric ammonium sulfate TS,and titrate the excess silver nitrate with 0.1Nammonium thiocyanate VS.Each mLof 0.1Nsilver nitrate is equivalent to 3.545mg of Cl.Not more than 0.16%of chloride is found.
Assay— To about 20g of Gel,accurately weighed,in a 100-mLvolumetric flask,add nitric acid to effect solution,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a 400-mLbeaker,dilute with water to 100mL,heat to 60,add an excess of ammonium molybdate TS,and maintain at 50for 30minutes.Filter,and wash the precipitate with dilute nitric acid (1in 36),then with potassium nitrate solution (1in 100)until the last portion of the filtrate is not acid to litmus paper.Dissolve the precipitate in 50.0mLof 0.5Nsodium hydroxide VS,add phenolphthalein TS,and titrate the excess sodium hydroxide with 0.5Nsulfuric acid VS.Each mLof 0.5Nsodium hydroxide is equivalent to 2.651mg of AlPO4.
Auxiliary Information— Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 94
Pharmacopeial Forum:Volume No.27(6)Page 3242
Phone Number:1-301-816-8251