Dibasic Calcium Phosphate Dihydrate
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Attribute JP EP USP
Definition + + +
Identification A + + +
Identification B + + +
Acid-insoluble substances + + +
Chloride + + +
Sulfate + + +
Carbonate + + +
Barium + + +
Loss on ignition + + +
Assay + + +
Legend: + will adopt and implement; - will not stipulate.
Nonharmonized attributes: Packaging and storage, Heavy metals, Limit of fluoride, Iron.
Specific local attributes: Identification C (EP), Lead (USP), Description (JP)

Phosphoric acid, calcium salt (1:1).

Calcium phosphate, Dihydrate (1:1) [7789-77-7].
» Dibasic Calcium Phosphate Dihydrate contains two molecules of water of hydration. It contains not less than 98.0 percent and not more than 105.0 percent of dibasic calcium phosphate dihydrate (CaHPO4·2H2O).
Packaging and storage— Preserve in well-closed containers. No storage requirements specified.
USP Reference standards 11
USP Sodium Fluoride RS
A: Dissolve about 100 mg by warming in 10 mL of 2 N hydrochloric acid, add 2.5 mL of ammonia TS dropwise, with shaking, and then add 5 mL of ammonium oxalate TS: a white precipitate is formed.
Ammonium molybdate solution— Dissolve 21.2 g of ammonium molybdate in water to make 200 mL of solution (10%). Prepare before use.
Dissolve about 100 mg of sample in 5 mL of diluted nitric acid. Warm the solution to 70, and add 2 mL of Ammonium molybdate solution: a yellow precipitate of ammonium phosphomolybdate is formed.
Loss on ignition 733 Ignite about 1 g at 800 to 825 to constant weight: the material loses between 24.5% and 26.5% of its weight.
Carbonate— Mix 1.0 g with 5 mL of carbon dioxide-free water, and immediately add 2 mL of hydrochloric acid: no effervescence occurs.
Chloride 221 To 0.20 g add 20 mL of water and 13 mL of diluted nitric acid, and warm gently, if necessary, until no more dissolves. Dilute to 100 mL, and filter, if necessary. To 50 mL of this solution add 1 mL of silver nitrate TS: the turbidity does not exceed that produced by 0.70 mL of 0.010 N hydrochloric acid (0.25%).
Sulfate 221 Dissolve 0.5 g in 5 mL of water and 5 mL of diluted hydrochloric acid, dilute with water to 100 mL, and filter, if necessary. To 20 mL of the filtrate add 1 mL of diluted hydrochloric acid, and dilute with water to 50 mL. Add 1 mL of barium chloride TS: the turbidity does not exceed that produced by 1.0 mL of 0.010 N sulfuric acid (0.5%).
Arsenic, Method I 211 Prepare the Test Preparation by dissolving 1.0 g in 25 mL of 3 N hydrochloric acid, and diluting with water to 55 mL: the resulting solution meets the requirements of the test, the addition of 20 mL of 7 N sulfuric acid specified under Procedure being omitted. The limit is 3 µg per g.
Barium— Heat to boiling 0.50 g with 10 mL of water, and add 1 mL of hydrochloric acid dropwise, stirring after each addition. Allow to cool, and filter, if necessary, and to the filtrate add 2 mL of potassium sulfate TS: no turbidity is produced within 10 minutes.
Heavy metals, Method I 231 Warm 1.3 g with 3 mL of 3 N hydrochloric acid until no more dissolves, dilute with water to 50 mL, and filter: the limit is 0.003%.
Limit of acid-insoluble substances— Dissolve 5.0 g with a mixture of 40 mL of water and 10 mL of hydrochloric acid by boiling gently for 5 minutes. After cooling, collect the insoluble substance on ashless filter paper, and wash with water until the last washing does not give a reaction for chloride (no turbidity results from the addition of silver nitrate TS.) Ignite to incinerate completely the residue and ashless filter paper for assay at 600 ± 50. The weight of the residue does not exceed 10 mg: 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 73.5 g of sodium citrate dihydrate in water to make 250 mL of solution.
Standard solution— Dissolve an accurately weighed quantity of USP Sodium Fluoride RS quantitatively in water to obtain a solution containing 1.1052 mg per mL. Transfer 20.0 mL of the resulting solution to a 100-mL volumetric flask containing 50 mL of Buffer solution, dilute with water to volume, and mix. Each mL of this solution contains 100 µg of fluoride ion.
Electrode system— Use a fluoride-specific, ion-indicating electrode and a silver–silver chloride reference electrode connected to a pH meter capable of measuring potentials with a minimum reproducibility of ±0.2 mV (see pH 791).
Standard response line— Transfer 50.0 mL of Buffer solution and 2.0 mL of hydrochloric acid to a beaker, and add water to make 100 mL. Add a plastic-coated stirring bar, insert the electrodes into the solution, stir for 15 minutes, and read the potential, in mV. Continue stirring, and at 5-minute intervals add 100 µL, 100 µL, 300 µL, and 500 µL of Standard solution, reading the potential 5 minutes after each addition. Plot the logarithms of the cumulative fluoride ion concentrations (0.1 µg per mL, 0.2 µg per mL, 0.5 µg per mL, and 1.0 µg per mL) versus potential, in mV.
Procedure— Transfer 2.0 g of the specimen under test to a beaker containing a plastic-coated stirring bar, add 20 mL of water and 2.0 mL of hydrochloric acid, and stir until dissolved. Add 50.0 mL of Buffer solution and sufficient water to make 100 mL of test solution. Rinse and dry the electrodes, insert them into the test solution, stir for 5 minutes, and read the potential, in mV. From the measured potential and the Standard response line determine 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 C by 0.005: the limit is 0.005%.
Ammonia–ammonium chloride buffer, pH 10.7— Dissolve 53.5 g of ammonium chloride in water. Add 570 mL of ammonia water, stronger. Dilute with water to make 1000 mL.
Transfer about 400 mg of Dibasic Calcium Phosphate Dihydrate, accurately weighed, into a 200-mL volumetric flask. Dissolve in 12 mL of diluted hydrochloric acid with the aid of gentle heat, if necessary, and dilute with water to volume. Transfer 20.0 mL of this solution to a solution containing 25.0 mL of 0.02 M edetate disodium VS, 50 mL of water, and 5 mL of Ammonia–ammonium chloride buffer, pH 10.7. Add 25 mg of eriochrome black T–sodium chloride, and titrate the excess edetate disodium with 0.02 M zinc sulfate VS. Perform a blank determination in the same manner. Each mL of 0.02 M edetate disodium is equivalent to 3.442 mg of CaHPO4·2H2O.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Curtis Phinney

(DSN05) Dietary Supplements - Non-Botanicals
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 1770
Pharmacopeial Forum: Volume No. 32(4) Page 1329
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.