Magnesium Stearate [557-04-0] 

This product is a compound of magnesium and stearic acid. It is a mixture mainly composed of magnesium stearate (C36H70MgO4) and magnesium palmitate (C32H62MgO4). Calculated on the dried basis, it contains not less than 4.0% and not more than 5.0% of Mg. 【Description】This product is a white, light, non-sandy fine powder; it has a slight characteristic odor; it has a smooth and greasy feel when in contact with the skin. This product is insoluble in water and ethanol.

【Identification】(1) Take 5.0g of the product, place it in a round-bottom flask, add 50ml of peroxide-free ether, 20ml of dilute nitric acid, and 20ml of water, heat under reflux until completely dissolved, cool, transfer to a separatory funnel, shake, allow to stand for layering, transfer the aqueous layer to another separatory funnel; extract the ether layer with water twice, 4ml each time, combine the aqueous layers; wash the aqueous layer with 15ml of peroxide-free ether, transfer the aqueous layer to a 50ml volumetric flask, dilute with water to volume, and mix well. Use this as the test solution, which should show the identification reaction for magnesium salts (General Rule 0301).     (2) In the chromatogram recorded under the test for relative content of stearic acid and palmitic acid, the retention times of the two main peaks in the chromatogram of the test solution should correspond to those of the two main peaks in the chromatogram of the reference solution.

 Percentage content of stearic acid (%) = A/B × 100%     Where A is the peak area of methyl stearate in the test sample; B is the peak area of all fatty acid esters in the test sample. Similarly, calculate the percentage content of palmitic acid in the total fatty acids in magnesium stearate. The relative content of stearic acid should not be less than 40%, and the sum of the relative contents of stearic acid and palmitic acid should not be less than 90%.  

 Microbial Limits Take the product, and examine as directed (General Rule 1105 and General Rule 1106). The total aerobic microbial count should not exceed 1000 cfu per 1g of the test sample, the total combined yeasts and molds count should not exceed 100 cfu per 1g, and Escherichia coli should not be detected. 

【Assay】Take about 0.2g of the product, accurately weighed, add 50ml of a solution of n-butanol and anhydrous ethanol (1:1), add 5ml of concentrated ammonia solution and 3ml of ammonia-ammonium chloride buffer (pH 10.0), then accurately add 25ml of disodium edetate titrant (0.05mol/L) and a small amount of eriochrome black T indicator, mix well, heat on a water bath at 40-50°C until the solution becomes clear, titrate with zinc titrant (0.05mol/L) until the solution changes from blue to purple, and correct the titration result with a blank test. Each 1ml of disodium edetate titrant (0.05mol/L) is equivalent to 1.215mg of Mg.    

【Category】Pharmaceutical excipient, lubricant.

【Storage】Preserve in a tightly closed container.