Dibasic Calcium Phosphate
CaHPO4 136.06

Phosphoric acid,calcium salt (1:1).

Calcium phosphate (1:1) [7757-93-9].

Dihydrate 172.09 [7789-77-7].
»Dibasic Calcium Phosphate is anhydrous or contains two molecules of water of hydration.It contains not less than 98.0percent and not more than 105.0percent of anhydrous dibasic calcium phosphate (CaHPO4)or of dibasic calcium phosphate dihydrate (CaHPO4·2H2O).
Packaging and storage— Preserve in well-closed containers.
Labeling— Label it to indicate whether it is anhydrous or the dihydrate.
Identification—
A: Dissolve about 100mg by warming with a mixture of 5mLof 3Nhydrochloric acid and 5mLof water,add 2.5mLof 6Nammonium hydroxide dropwise,with shaking,and then add 5mLof ammonium oxalate TS:a white precipitate is formed.
B: To 10mLof a warm solution (1in 100)in a slight excess of nitric acid add 10mLof ammonium molybdate TS:a yellow precipitate of ammonium phosphomolybdate is formed.
Loss on ignition á733ñ— Ignite it at 800to 825to constant weight:anhydrous Dibasic Calcium Phosphate loses between 6.6%and 8.5%of its weight,and the dihydrate form of Dibasic Calcium Phosphate loses between 24.5%and 26.5%of its weight.
Carbonate— Mix 1.0g with 5mLof water,and add 2mLof hydrochloric acid:no effervescence occurs.
Chloride á221ñ— To 0.30g add 10mLof water and 2mLof nitric acid,and warm gently,if necessary,until no more dissolves.Dilute to 25mL,filter,if necessary,and add 1mLof silver nitrate TS:the turbidity does not exceed that produced by 1.0mLof 0.020Nhydrochloric acid (0.25%).
Sulfate á221ñ— Dissolve 1.0g in the smallest possible amount of 3Nhydrochloric acid,dilute with water to 100mL,and filter,if necessary.To 20mLof the filtrate add 1mLof barium chloride TS:the turbidity does not exceed that produced by 1.0mLof 0.020Nsulfuric acid (0.5%).
Arsenic,Method Iá211ñ— Prepare the Test Preparationby dissolving 1.0g in 25mLof 3Nhydrochloric acid and diluting with water to 55mL:the resulting solution meets the requirements of the test,the addition of 20mLof 7Nsulfuric acid specified under Procedurebeing omitted.The limit is 3µg per g.
Barium— Heat 0.50g with 10mLof water,and add hydrochloric acid dropwise,stirring after each addition,until no more dissolves.Filter,and to the filtrate add 2mLof potassium sulfate TS:no turbidity is produced within 10minutes.
Heavy metals,Method Iá231ñ— Warm 1.3g with 3mLof 3Nhydrochloric acid until no more dissolves,dilute with water to 50mL,and filter:the limit is 0.003%.
Limit of acid-insoluble substances— Heat 5.0g with a mixture of 40mLof water and 10mLof hydrochloric acid until no more dissolves,and dilute with water to 100mL.If an insoluble residue remains,filter,wash with hot water until the last washing does not give a reaction for chloride,and dry the residue at 105for 1hour.The weight of the residue does not exceed 10mg:not more than 0.2%of acid-insoluble substances is found.
Limit of fluoride— [NOTE—Prepare and store all solutions in plastic containers.]
Buffer solution— Dissolve 73.5g of sodium citrate dihydrate in water to make 250mLof solution.
Standard solution— Dissolve an accurately weighed quantity of USP Sodium Fluoride RSquantitatively in water to obtain a solution containing 1.1052mg per mL.Transfer 20.0mLof the resulting solution to a 100-mLvolumetric flask containing 50mLof Buffer solution,dilute with water to volume,and mix.Each mLof this solution contains 100µg of fluoride ion.
Electrode system— Use a fluoride-specific,ion-indicating electrode and a silver-silver chloride reference electrode connected to a pHmeter capable of measuring potentials with a minimum reproducibility of ±0.2mV(see pHá791ñ).
Standard response line— Transfer 50.0mLof Buffer solutionand 2.0mLof 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,and 500µLof Standard solution,reading the potential 5minutes after each addition.Plot the logarithms of the cumulative fluoride ion concentrations (0.1µg per mL,0.2µg per mL,0.5µg per mL,and 1.0µg per mL)versus potential,in mV.
Procedure— Transfer 2.0g of the specimen under test to a beaker containing a plastic-coated stirring bar,add 20mLof water and 2.0mLof hydrochloric acid,and stir until dissolved.Add 50.0mLof Buffer solutionand sufficient water to make 100mLof test solution.Rinse and dry the electrodes,insert them into the test solution,stir for 5minutes,and read the potential,in mV.From the measured potential and the Standard response linedetermine the concentration,C,in µg per mL,of fluoride ion in the test solution.Calculate the percentage of fluoride in the specimen taken by multiplying Cby 0.005:the limit is 0.005%.
Assay— Dissolve about 250mg of Dibasic Calcium Phosphate,accurately weighed,with the aid of gentle heat if necessary,in a mixture of hydrochloric acid and water (5:3)contained in a 250-mLbeaker equipped with a magnetic stirrer,and cautiously add 125mLof water.With constant stirring,add,in the order named,0.5mLof triethanolamine,300mg of hydroxy naphthol blue,and,from a 50-mLburet,about 23mLof 0.05Medetate disodium VS.Add sodium hydroxide solution (45in 100)until the initial red color changes to clear blue.Continue to add it dropwise until the color changes to violet,and add an additional 0.5mL.The pHis between 12.3and 12.5.Continue the titration dropwise with the 0.05Medetate disodium VSto the appearance of a clear blue endpoint that persists for not less than 60seconds.Each mLof 0.05Medetate disodium is equivalent to 6.803mg of CaHPO4or to 8.604mg of CaHPO4·2H2O.
Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(DSN)Dietary Supplements:Non-Botanicals
USP28–NF23Page 332
Pharmacopeial Forum:Volume No.27(6)Page 3261
Phone Number:1-301-816-8389