Tribasic Calcium Phosphate
Ca5(OH)(PO4)3 502.31

Calcium hydroxide phosphate (Ca5(OH)(PO4)3).
Calcium hydroxide phosphate (Ca5(OH)(PO4)3) [12167-74-7].
»Tribasic Calcium Phosphate consists of a variable mixture of calcium phosphates having the approximate composition 10CaO·3P2O5·H2O.It contains not less than 34.0percent and not more than 40.0percent of calcium (Ca).
Packaging and storage— Preserve in well-closed containers.
Identification—
A: To a warm solution in a slight excess of nitric acid add ammonium molybdate TS:a yellow precipitate is formed.
B: It responds to the flame test for Calcium á191ñ.
Loss on ignition á733ñ— Ignite it at 800for 30minutes:it loses not more than 8.0%of its weight.
Water-soluble substances— Digest 2g with 100mLof water on a steam bath for 30minutes,cool,add sufficient water to restore the original volume,stir well,and filter.Evaporate 50mLof the filtrate in a tared porcelain dish on a steam bath to dryness,and dry the residue at 120to constant weight:the weight of the residue does not exceed 5mg (0.5%).
Acid-insoluble substances— If an insoluble residue remains in the test for Carbonate,boil the solution,filter,wash the residue well with hot water until the last washing is free from chloride,and ignite the residue to constant weight:the weight of the residue does not exceed 4mg (0.2%).
Carbonate— Mix 2g with 20mLof water,and add 3Nhydrochloric acid,dropwise,to effect solution:no effervescence is produced.
Chloride á221ñ— Dissolve 500mg in 25mLof 2Nnitric acid,and add 1mLof silver nitrate TS:the turbidity does not exceed that produced by 1.0mLof 0.020Nhydrochloric acid (0.14%).
Sulfate á221ñ— Dissolve 500mg in the smallest possible amount of 3Nhydrochloric acid,dilute with water to 100mL,filter,if necessary,and to 25mLof the filtrate add 1mLof barium chloride TS:the turbidity does not exceed that produced by 1.0mLof 0.020Nsulfuric acid (0.8%).
Arsenic,Method Iá211ñ— Prepare the Test Preparationby dissolving 1.0g in just sufficient 3Nhydrochloric acid to dissolve the test specimen.The limit is 3ppm.
Barium— Mix 500mg with 10mLof water,heat,add hydrochloric acid,dropwise,until solution is effected,and then add 2drops of the acid in excess.Filter,and add to the filtrate 1mLof potassium sulfate TS:no turbidity appears within 15minutes.
Dibasic salt and calcium oxide— Weigh accurately about 1.5g,and dissolve by warming with 25.0mLof 1Nhydrochloric acid VS.Cool,and slowly titrate the excess of 1Nhydrochloric acid,while agitating constantly,with 0.1Nsodium hydroxide VSto a pHof 4.0,determined potentiometrically.Not less than 13.0mLand not more than 14.3mLof 1Nhydrochloric acid is consumed for each g of salt,calculated on the ignited basis.
Limit of fluoride— [NOTE—Prepare and store all solutions in plastic containers.]
Buffer solution ,Standard solution,and Electrode system—Proceed as directed in the test for Limit of Fluoride under Dibasic Calcium Phosphate.
Standard response line— Transfer 50.0mLof Buffer solutionand 3.0mLof hydrochloric acid to a beaker,and add water to make 100mL.Add a plastic-coated stirring bar,insert the electrodes into the solution,stir for 15minutes,and read the potential,in mV.Continue stirring,and at 5-minute intervals add 100µL,100µL,300µL,500µL,and 500µLof Standard solution,reading the potential 5minutes after each addition.Plot the logarithms of the cumulative fluoride ion concentrations (0.1,0.2,0.5,1.0,and 1.5µg per mL)versus potential,in mV.
Procedure— Proceed as directed in the test for Limit of Fluorideunder Dibasic Calcium Phosphate,except to use 3.0mLof hydrochloric acid,instead of 2.0mL.The limit is 0.0075%.
Limit of nitrate— Mix 200mg with 5mLof water,and add just sufficient hydrochloric acid to effect solution.Dilute with water to 10mL,add 0.20mLof indigo carmine TS,then add,with stirring,10mLof sulfuric acid:the blue color persists for not less than 5minutes.
Heavy metals,Method Iá231ñ— Mix 1.3g with 9mLof 3Nhydrochloric acid,dilute with water to 50mL,and heat to boiling.Cool to room temperature,and filter.[NOTE—Filter the mixture after the pHadjustment]:the limit is 0.003%.
Assay— Weigh accurately about 150mg of Tribasic Calcium Phosphate,and proceed as directed in the Assay underDibasic Calcium Phosphate,beginning with “dissolve,with the aid of gentle heat.”Each mLof 0.05Medetate disodium is equivalent to 2.004mg of Ca.
Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(DSN)Dietary Supplements:Non-Botanicals
USP28–NF23Page 2969
Phone Number:1-301-816-8389