Mg3(PO4)2·5H2O 352.93

Phosphoric acid,magnesium salt (2:3),pentahydrate.
Magnesium phosphate (3:2)pentahydrate [10233-87-1].

Anhydrous 262.86 [7757-87-1].

Packaging and storage— Preserve in well-closed containers.

Identification—

Microbial limits á61ñ— It meets the requirements of the test for absence of Escherichia coli.

Loss on ignition á733ñ— Ignite it at 425to constant weight:it loses between 20.0%and 27.0%of its weight.

Acid-insoluble substances— If an insoluble residue remains in the test for Carbonate,filter the solution,wash well with hot water until the last washing is free from chloride,and ignite the residue:the weight of the residue does not exceed 4mg (0.2%).

Soluble substances— Digest 2.0g with 100mLof water on a steam bath for 30minutes,cool,add sufficient water to restore the original volume,mix,and filter.Evaporate 50mLof the filtrate to dryness,and ignite gently to constant weight:the weight of the residue does not exceed 15mg (1.5%).

Carbonate— Mix 2.0g with 20mLof water,and add hydrochloric acid,dropwise,to effect solution:no effervescence occurs when the acid is added.

Chloride á221ñ— Dissolve 0.50g in 50mLof 2Nnitric acid,and add 1mLof silver nitrate TS:the turbidity does not exceed that produced by 1.0mLof 0.020Nhydrochloric acid (0.14%).

Limit of nitrate— Mix 0.20g with 5mLof water,and add just sufficient hydrochloric acid to effect solution.Dilute with water to 10mL,add 0.1mLof indigo carmine TS,then add,with stirring,10mLof sulfuric acid:the blue color persists for not less than 5minutes.

Sulfate á221ñ— Dissolve 0.50g in the smallest possible amount of 3Nhydrochloric acid,dilute with water to 48mL,and add 2mLof barium chloride TS:the turbidity does not exceed that produced by 3.0mLof 0.020Nsulfuric acid (0.6%).

Arsenic,Method Iá211ñ— Prepare a Test Preparationby dissolving 1.0g in just sufficient 3Nhydrochloric acid (about 9mL)to dissolve the specimen.The limit is 3ppm.

Barium— Mix 2.0g with 40mLof water,heat,add hydrochloric acid,dropwise,to effect solution,and then add 1mLof acid in excess.Cool,dilute with water to 50mL,and filter.To 5mLof the filtrate add 1mLof potassium sulfate TS:no turbidity is produced within 15minutes.

Calcium— Mix 0.50g with 15mLof water,heat,and add sufficient hydrochloric acid,in small portions,to effect solution.Cool,add 6Nammonium hydroxide,in small portions,to produce a slight permanent precipitate,then add 2mLof 6Nacetic acid.Dilute with water to 25mL,and filter.To 10mLof the filtrate add 2mLof ammonium oxalate TS:not more than a slight turbidity is produced within 5minutes.

Dibasic salt and magnesium oxide— Ignite about 2.5g to constant weight.Weigh accurately about 2g of ignited salt,and dissolve it by warming with 50.0mLof 1Nhydrochloric acid VS.Cool,add 1or 2drops of methyl orange TS,and slowly titrate the excess 1Nhydrochloric acid VSwith 1Nsodium hydroxide VSto a yellow color,vigorously shaking the mixture during the titration.Between 14.8and 15.4mLof 1Nhydrochloric acid is consumed for each g of the ignited salt.

Lead á251ñ— Prepare a Test Preparationby dissolving 1.0g in 20mLof 3Nhydrochloric acid,evaporating on a steam bath to about 10mL,diluting with water to about 20mL,and cooling.Use 5mLof Diluted Standard Lead Solution(5µg of Pb)for the test:the limit is 5ppm.

Heavy metals,Method Iá231ñ— Dissolve 0.67g in 4.5mLof 3Nhydrochloric acid,and dilute with water to 25mL:the limit is 0.003%.

Assay— Weigh accurately about 200mg of Magnesium Phosphate,previously ignited at 425to constant weight,and dissolve in a mixture of 25mLof water and 10mLof 2Nnitric acid.Filter,if necessary,wash any precipitate,add sufficient 6Nammonium hydroxide to the filtrate to produce a slight precipitate,and then dissolve the precipitate by the addition of 1mLof 2Nnitric acid.Adjust the temperature to about 50,add 75mLof ammonium molybdate TS,and maintain the temperature at about 50for 30minutes,stirring occasionally.Wash the precipitate once or twice with water by decantation,using from 30to 40mLeach time and passing the washings through a filter.Transfer the precipitate to the filter,and wash with potassium nitrate solution (1in 100)until the last washing is not acid to litmus.Transfer the precipitate and filter to the precipitation vessel,add 50mLof water and 40.0mLof 1Nsodium hydroxide VS,agitate until the precipitate is dissolved,add phenolphthalein TS,and then titrate the excess alkali with 1Nsulfuric acid VS.Each mLof 1Nsodium hydroxide is equivalent to 5.716mg of Mg3(PO4)2.

Expert Committee:(PA4)Pharmaceutical Analysis 4

USP28–NF23Page 1173

Phone Number:1-301-816-8251