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.
Water-soluble substances—
Digest 2 g with 100 mL of water on a steam bath for 30 minutes, cool, add sufficient water to restore the original volume, stir well, and filter. Evaporate 50 mL of the filtrate in a tared porcelain dish on a steam bath to dryness, and dry the residue at 120
to constant weight: the weight of the residue does not exceed 5 mg (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 4 mg (0.2%).
Carbonate—
Mix 2 g with 20 mL of water, and add 3 N hydrochloric acid, dropwise, to effect solution: no effervescence is produced.
Chloride 
221
—
Dissolve 500 mg in 25 mL of 2 N nitric acid, and add 1 mL of
silver nitrate TS: the turbidity does not exceed that produced by 1.0 mL of 0.020 N hydrochloric acid (0.14%).
Sulfate 221—
Dissolve 500 mg in the smallest possible amount of 3 N hydrochloric acid, dilute with water to 100 mL, filter, if necessary, and to 25 mL of the filtrate add 1 mL of
barium chloride TS: the turbidity does not exceed that produced by 1.0 mL of 0.020 N sulfuric acid (0.8%).
Arsenic, Method I 211—
Prepare the
Test Preparation by dissolving 1.0 g in just sufficient 3 N hydrochloric acid to dissolve the test specimen. The limit is 3 ppm.
Barium—
Mix 500 mg with 10 mL of water, heat, add hydrochloric acid, dropwise, until solution is effected, and then add 2 drops of the acid in excess. Filter, and add to the filtrate 1 mL of
potassium sulfate TS: no turbidity appears within 15 minutes.
Dibasic salt and calcium oxide—
Weigh accurately about 1.5 g, and dissolve by warming with 25.0 mL of 1 N hydrochloric acid VS. Cool, and slowly titrate the excess of 1 N hydrochloric acid, while agitating constantly, with 0.1 N sodium hydroxide VS to a pH of 4.0, determined potentiometrically. Not less than 13.0 mL and not more than 14.3 mL of 1 N hydrochloric 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 50.0 mL of Buffer solution and 3.0 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, 500 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, 0.2, 0.5, 1.0, and 1.5 µg per mL) versus potential, in mV.
Procedure—
Proceed as directed in the test for Limit of Fluoride under Dibasic Calcium Phosphate, except to use 3.0 mL of hydrochloric acid, instead of 2.0 mL. The limit is 0.0075%.
Limit of nitrate—
Mix 200 mg with 5 mL of water, and add just sufficient hydrochloric acid to effect solution. Dilute with water to 10 mL, add 0.20 mL of indigo carmine TS, then add, with stirring, 10 mL of sulfuric acid: the blue color persists for not less than 5 minutes.
Heavy metals, Method I 231—
Mix 1.3 g with 9 mL of 3 N hydrochloric acid, dilute with water to 50 mL, and heat to boiling. Cool to room temperature, and filter.
[NOTE—Filter the mixture after the pH adjustment
]: the limit is 0.003%.
Assay—
Weigh accurately about 150 mg of Tribasic Calcium Phosphate, and proceed as directed in the Assay under Dibasic Calcium Phosphate, beginning with “dissolve, with the aid of gentle heat.” Each mL of 0.05 M edetate disodium is equivalent to 2.004 mg of Ca.
