Packaging and storage—
Preserve in well-closed containers.
Labeling—
The quantity of dibasic calcium phosphate stated in the labeling is in terms of CaHPO4·2H2O.
Identification—
A:
A filtered portion of the solution prepared for the
Assay responds to the tests for
Calcium 
191
.
B:
A filtered portion of the solution prepared for the
Assay, neutralized with ammonium hydroxide, responds to the tests for
Phosphate 191.
Dissolution 711—
Medium:
0.1 N hydrochloric acid, 900 mL.
Apparatus 2:
75 rpm.
Time:
45 minutes.
Procedure—
Determine the amount of CaHPO4·2H2O dissolved, employing atomic absorption spectrophotometry at a wavelength of about 422.7 nm in filtered portions of the solution under test, suitably diluted with Dissolution Medium if necessary, in comparison with a Standard solution having a known concentration of calcium in the same medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of CaHPO4·2H2O is dissolved in 45 minutes.
Assay—
Weigh and finely powder not fewer than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 1 g of dibasic calcium phosphate (dihydrate), and transfer to a 100-mL volumetric flask containing 15 mL of hydrochloric acid and 10 mL of water. Heat on a steam bath, with occasional mixing to dissolve the dibasic calcium phosphate, but not longer than 30 minutes. Cool, add water to volume, and mix. If the preparation is not clear, filter, discarding the first 10 mL of the filtrate (reserve portions of the solution for the
Identification tests). Transfer 25.0 mL of the solution to a 250-mL beaker equipped with a magnetic stirrer. Proceed as directed in the
Assay under
Dibasic Calcium Phosphate, beginning with “With constant stirring.” Each mL of 0.05
M edetate disodium is equivalent to 8.604 mg of CaHPO
4·2H
2O.
