CaCO3 100.09

Carbonic acid, calcium salt (1:1).

Calcium carbonate (1:1) [471-34-1].

Packaging and storage— Preserve in well-closed containers.

Identification— The addition of acetic acid to it produces effervescence (presence of carbonate), and the resulting solution, after boiling, responds to the tests for Calcium 191.

Loss on drying 731— Dry it at 200 for 4 hours: it loses not more than 2.0% of its weight.

Acid-insoluble substances— Mix 5.0 g with 10 mL of water, and add hydrochloric acid, dropwise, with agitation, until it ceases to cause effervescence, then add water to make the mixture measure 200 mL, and filter. Wash the insoluble residue with water until the last washing shows no chloride, and ignite: the weight of the residue does not exceed 10 mg (0.2%).

Limit of fluoride— [note—Prepare and store all solutions in plastic containers.]

Arsenic, Method I 211— Slowly dissolve 1.0 g in 15 mL of hydrochloric acid, and dilute 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 ppm.

Barium— A platinum wire, dipped in the filtrate obtained in the test for Acid-insoluble substances and held in a nonluminous flame, does not impart a green color.

Lead 251— Mix 1.0 g with 5 mL of water, slowly add 8 mL of 3 N hydrochloric acid, evaporate on a steam bath to dryness, and dissolve the residue in 5 mL of water: the limit is 3 ppm.

Iron— Dissolve 40 mg in 5 mL of 2 N hydrochloric acid, transfer to a beaker with the aid of water, and dilute with water to 10 mL. Prepare a Standard solution by transferring 4.0 mL of Standard Iron Solution, prepared as directed under Iron 241, to a beaker and by diluting with water to 10 mL. To each beaker add 2 mL of citric acid solution (1 in 5) and 2 drops of thioglycolic acid, adjust to a pH of 9.5 ± 0.1 with ammonia TS, dilute with water to 20 mL, mix, and allow to stand for 5 minutes. Dilute with water to 50 mL, and mix. Concomitantly determine the absorbances of the solutions from the specimen and the Standard solution at the wavelength of maximum absorbance at about 530 nm with a suitable spectrophotometer, using water as the blank: the absorbance of the solution from the specimen under test does not exceed that of the Standard solution (0.1%).

Mercury, Method IIa 261— Transfer 4.0 g to a 100-mL beaker, and cautiously dissolve in 14 mL of 6 N hydrochloric acid. Use 3 mL of hydrochloric acid instead of 3 mL of sulfuric acid when preparing the Standard Preparation and the Test Preparation: the limit is 0.5 µg per g.

Limit of magnesium and alkali salts— Mix 1.0 g with 35 mL of water, carefully add 3 mL of hydrochloric acid, heat the solution, and boil for 1 minute. Rapidly add 40 mL of oxalic acid TS, and stir vigorously until precipitation is well established. Add immediately to the warm mixture 2 drops of methyl red TS and then 6 N ammonium hydroxide, dropwise, until the mixture is just alkaline. Cool to room temperature, transfer to a 100-mL graduated cylinder, dilute with water to 100 mL, mix, and allow to stand for 4 hours or overnight. Filter, and to 50 mL of the clear filtrate in a platinum dish add 0.5 mL of sulfuric acid, and evaporate the mixture on a steam bath to a small volume. Carefully heat over a free flame to dryness, and continue heating to complete decomposition and volatilization of ammonium salts. Finally ignite the residue to constant weight. The weight of the residue does not exceed 5 mg (1.0%).

Heavy metals 231— Mix 1.0 g with 5 mL of water, slowly add 8 mL of 3 N hydrochloric acid, and evaporate on a steam bath to dryness. Dissolve the residue in 20 mL of water, filter, and add water to the filtrate to make 25 mL: the limit is 0.002%.

Assay— Transfer about 200 mg of Calcium Carbonate, previously dried at 200 for 4 hours and accurately weighed, to a 250-mL beaker. Moisten thoroughly with a few mL of water, and add, dropwise, sufficient 3 N hydrochloric acid to dissolve. Add 100 mL of water, 15 mL of 1 N sodium hydroxide, and 300 mg of hydroxy naphthol blue, and titrate with 0.05 M edetate disodium VS until the solution is a distinct blue in color. Each mL of 0.05 M edetate disodium is equivalent to 5.004 mg of CaCO3.

Topic/Question	Contact	Expert Committee
Monograph	Curtis Phinney 1-301-816-8345	(DSN05) Dietary Supplements - Non-Botanicals

USP32–NF27 Page 1754

CALCIUM CARBONATE

Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.