Monographs: Pharmaceutical substances: Calcium stearate (Calcii stearas)
Chemical name. Calcium stearate; calcium octadecanoate; CAS Reg. No. 1592-23-0.
Description. A white to yellowish white, fine, bulky powder; odour, slight, characteristic.
Solubility. Practically insoluble in water, ethanol (~750 g/l) TS, acetone R, and ether R.
Category. Tablet and capsule lubricant.
Storage. Calcium stearate should be kept in a well-closed container.
Additional information. The degree of lubrication depends on the particular form and size of the material.
Definition. Calcium stearate consists of calcium salts mainly of stearic acid and palmitic acid in variable proportions.
Calcium stearate contains not less than 9.0% and not more than the equivalent of 10.5% of CaO, calculated with reference to the dried substance.
Loss on drying. Heat at 105 °C for 2 hours and weigh; repeat the heating using 2-hour increments until a constant mass is obtained; not more than 40 mg/g.
Assay. To about 1.2 g, accurately weighed, add 50 mL of hydrochloric acid (0.1 mol/l) V, and heat to boiling for 10 minutes or until the separated fatty acids layer is clear, adding water if necessary to maintain the original volume. Cool, filter, and wash the filter and the flask thoroughly with water until the washing is free from acid when tested with litmus paper R. Neutralize the filtrate with sodium hydroxide (1 mol/l) VS against litmus paper R and proceed with the titration as described under 2.5 Complexometric titrations for calcium.
Each mL of disodium edetate (0.05 mol/l) VS is equivalent to 2.804 mg of CaO.