Tribasic Sodium Phosphate
Na3PO4(anhydrous) 163.94

Phosphoric acid,trisodium salt,dodecahydrate.
Trisodium phosphate,dodecahydrate 380.13 [10101-89-0].

Trisodium phosphate,monohydrate 181.96
Anhydrous [7601-54-9].
»Tribasic Sodium Phosphate is anhydrous or contains one to twelve molecules of water of hydration.Na3PO4(anhydrous)and Na3PO4·H2O(monohydrate)contain not less than 97.0percent of Na3PO4,calculated on the ignited basis;Na3PO4·12H2O(dodecahydrate)contains not less than 92.0percent of Na3PO4,calculated on the ignited basis.
Packaging and storage— Preserve in tight containers.Store at room temperature,and avoid excessive heat and freezing.Protect from moisture.
Labeling— Label it to indicate whether it is anhydrous,the monohydrate,or the dodecahydrate.
Identification— Asolution (1in 20)meets the requirements of the tests for Sodium á191ñand for Phosphate á191ñ.
Loss on ignition á733ñ— Dry a portion at 100for 5hours.Ignite about 2g,accurately weighed,of the dried sample at about 800for 30minutes:calculated on the dried basis,the anhydrous form loses not more than 2.0%of its weight,the monohydrate loses between 8.0%and 11.0%of its weight,and the dodecahydrate loses between 45.0%and 57.0%of its weight.
Insoluble substances— Dissolve a portion equivalent to 10.0g of anhydrous tribasic sodium phosphate in 100mLof hot water,and filter through a tared filtering crucible.[NOTE—Do not use glass.]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%).
Arsenic,Method Iá211ñ— Dissolve a portion equivalent to 1.0g of anhydrous tribasic sodium phosphate in 35mLof water:3µg per g.
Heavy metals,Method Iá231ñ— Dissolve a portion equivalent to 2.0g of anhydrous tribasic sodium phosphate in 25mLof water:0.001%.
Assay— Transfer 100.0mLof 1Nhydrochloric acid to a 400-mLbeaker,and titrate potentiometrically with 1Nsodium hydroxide VSto the endpoint at a pHof 7.0.Record the volume of 1Nsodium hydroxide VSconsumed as the blank.Transfer a portion of Tribasic Sodium Phosphate,accurately weighed,equivalent to about 5.5g of anhydrous tribasic sodium phosphate,to a 400-mLbeaker,add 100.0mLof 1Nhydrochloric acid,and stir until dissolved.Pass a stream of carbon-dioxide free air,in fine bubbles,through the solution for 30minutes to expel carbon dioxide,covering the beaker loosely to prevent any loss by spraying.Wash the cover and sides of the beaker with a few mLof water.Titrate the excess acid potentiometrically with 1Nsodium hydroxide VSto the inflection point at about pH4,and record the buret reading.Subtract this buret reading from that of the blank,and designate the volume of 1Nsodium hydroxide VSresulting from the subtraction as A.
Protect the solution from carbon dioxide absorbed from the air,and continue the titration with 1Nsodium hydroxide VSto the inflection point at a pHof about 8.8,record the buret reading,and calculate the volume of 1Nsodium hydroxide required in the titration between the two inflection points (pH4to pH8.8)as B.WhereAis equal to or greater than 2B,each mLof the volume of Bof 1Nsodium hydroxide is equivalent to 163.9mg of Na3PO4.Where Ais less than 2B,each mLof the volume A–Bof 1Nsodium hydroxide is equivalent to 163.9mg of Na3PO4.Calculate the percentage of Na3PO4on the ignited basis in the portion of Tribasic Sodium Phosphate taken by the formula:
[10/(100–L)](D/W),
in whichLis the percentage calculated in the test for Loss on ignition;Dis the amount,in mg,of Na3PO4found;and Wis the weight,in g,of the sample.
Auxiliary Information— Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 3079
Pharmacopeial Forum:Volume No.30(3)Page 992
Phone Number:1-301-816-8251