Calcium Stearate

Octadecanoic acid, calcium salt.
Calcium stearate [1592-23-0].
» Calcium Stearate is a compound of calcium with a mixture of solid organic acids obtained from fats and consists chiefly of variable proportions of calcium stearate and calcium palmitate. It contains the equivalent of not less than 9.0 percent and not more than 10.5 percent of calcium oxide (CaO).
Packaging and storage— Preserve in well-closed containers.
A: Heat 1 g with a mixture of 25 mL of water and 5 mL of hydrochloric acid: fatty acids are liberated and appear as an oily layer floating on the surface of the liquid. The water layer responds to the tests for Calcium 191.
B: Mix 25 g with 200 mL of hot water, add 60 mL of 2 N sulfuric acid, and heat the mixture, with frequent stirring, until the separated fatty acid layer is clear. Wash the fatty acids with boiling water until free from sulfate, collect them in a small beaker, and warm on a steam bath until the water has separated and the fatty acids are clear. Allow the acids to cool, pour off the water layer, melt the acids, filter into a dry beaker, and dry at 105 for 20 minutes: the fatty acids so obtained congeal at a temperature not below 54 (see Congealing Temperature 651).
Loss on drying 731 Dry it at 105 to constant weight, using 2-hour increments of heating: it loses not more than 4.0% of its weight.
Heavy metals 231 Place 2.5 g in a porcelain dish, place a 500-mg portion in a second dish to provide the control, and to each add 5 mL of a 1 in 4 solution of magnesium nitrate in alcohol. Cover the dishes with 7.5-cm short-stem funnels so that the stems are straight up. Heat on a hot plate at low heat for 30 minutes, then heat at medium heat for 30 minutes, and cool. Remove the funnels, add 2 mL of Standard Lead Solution (20 µg of Pb) to the control, and heat each dish over a suitable burner until most of the carbon is burned off. Cool, add 10 mL of nitric acid, and transfer the solutions into 250-mL beakers. Add 5 mL of 70% perchloric acid, cautiously evaporate to dryness, add 2 mL of hydrochloric acid to the residues, and wash down the insides of the beakers with water. Evaporate carefully to dryness again, swirling near the dry point to avoid spattering. Repeat the hydrochloric acid treatment, then cool, and dissolve the residues in about 10 mL of water. To each solution add 1 drop of phenolphthalein TS and add sodium hydroxide TS until the solutions just turn pink, then add 3 N hydrochloric acid until the solutions become colorless. Add 1 mL of 1 N acetic acid and a small amount of charcoal to each solution, and filter through filter paper into 50-mL color-comparison tubes. Wash with water, dilute with water to 40 mL, add 1.2 mL of thioacetamide-glycerin base TS and 2 mL of pH 3.5 Acetate Buffer to each tube, and allow to stand for 5 minutes: the color of the test solution does not exceed that of the control. The limit is 10 µg per g.
Assay— Boil about 1.2 g of Calcium Stearate, accurately weighed, with 50 mL of 1 N sulfuric acid for about 3 hours using a watch glass cover to avoid splattering, or until the separated fatty acid layer is clear, adding water, if necessary, to maintain the original volume. [note—Stirring may be helpful in obtaining a clear layer and decreasing extraction time.] Cool, filter, and wash the filter and the flask thoroughly with water until the last washing is not acid to litmus. Neutralize the filtrate with 1 N sodium hydroxide to litmus. While stirring, preferably with a magnetic stirrer, titrate with 0.05 M edetate disodium VS as follows. Add about 30 mL from a 50-mL buret, then add 15 mL of 1 N sodium hydroxide and 300 mg of hydroxy naphthol blue, and continue the titration to a blue endpoint. Each mL of 0.05 M edetate disodium is equivalent to 2.804 mg of CaO.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, B.A.
(EM105) Excipient Monographs 1
USP32–NF27 Page 1182
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.