NaH2PO4·xH2O
(anhydrous) 119.98

Phosphoric acid,monosodium salt,monohydrate.
Monosodium phosphate monohydrate 137.99 [10049-21-5].

Phosphoric acid,monosodium salt,dihydrate.
Monosodium phosphate dihydrate 156.01 [13472-35-0].

Anhydrous [7558-80-7].

Packaging and storage— Preserve in well-closed containers.

Labeling— Label it to indicate whether it is anhydrous or is the monohydrate or the dihydrate.

Identification— Asolution (1in 20)responds to the tests for Sodium á191ñand for Phosphate á191ñ.

pHá791ñ: between 4.1and 4.5,in a solution containing the equivalent of 1.0g of NaH2PO4·H2Oin 20mLof water.

Water,Method Iá921ñ: less than 2.0%(anhydrous form);between 10.0%and 15.0%(monohydrate);between 18.0%and 26.5%(dihydrate).For the monohydrate,the sample may be ground to a fine powder in an atmosphere of temperature and relative humidity known not to influence the results,prior to performing the test.

Insoluble substances— Dissolve a portion equivalent to 10.0g of NaH2PO4·H2Oin 100mLof hot water,filter through a tared filtering crucible,wash the insoluble residue with hot water,and dry at 105for 2hours:the weight of the residue so obtained does not exceed 20mg (0.2%).

Chloride á221ñ— Aportion equivalent to 1.0g of NaH2PO4·H2Oshows no more chloride than corresponds to 0.20mLof 0.020Nhydrochloric acid (0.014%).

Sulfate á221ñ— Aportion equivalent to 0.20g of NaH2PO4·H2Oshows no more sulfate than corresponds to 0.30mLof 0.020Nsulfuric acid (0.15%).

Aluminum,calcium,and related elements— Asolution containing the equivalent of 1.0g of NaH2PO4·H2Oin 10mLof water does not become turbid when rendered slightly alkaline to litmus paper with 6Nammonium hydroxide.

Arsenic,Method Iá211ñ— Dissolve a portion equivalent to 0.375g of NaH2PO4·H2Oin 35mLof water:the limit is 8ppm.

Heavy metals á231ñ— Dissolve a portion equivalent to 1.0g of NaH2PO4·H2Oin 20mLof water,and add 1mLof 3Nhydrochloric acid and water to make 25mL:the limit is 0.002%.

Organic volatile impurities,Method Iá467ñ: meets the requirements.

Assay— Dissolve about 2.5g of Monobasic Sodium Phosphate,accurately weighed,in 10mLof cold water,add 20mLof a cold,saturated solution of sodium chloride,then add phenolphthalein TS,and titrate with 1Nsodium hydroxide VS,keeping the temperature of the solution between 10and 15during the entire titration.Perform a blank determination,and make any necessary correction.Each mLof 1Nsodium hydroxide is equivalent to 120.0mg of NaH2PO4.

Expert Committee:(PA4)Pharmaceutical Analysis 4

USP28–NF23Page 1791

Phone Number:1-301-816-8251