Packaging and storage—
Preserve in tight containers.
Labeling—
Where the labeling states the specific surface area, it also indicates which method specified under
Specific Surface Area 
846
is used.
Identification—
A:
Mix 5.0 g with 50 mL of peroxide-free ether, 20 mL of diluted nitric acid, and 20 mL of water in a round-bottom flask. Connect the flask to a reflux condenser, and reflux until dissolution is complete. Allow to cool, and transfer the contents of the flask to a separator. Shake, allow the layers to separate, and transfer the aqueous layer to a flask. Extract the ether layer with two 4-mL portions of water, and add these aqueous extracts to the main aqueous extract. Wash the aqueous extract with 15 mL of peroxide-free ether, transfer the aqueous extract to a 50-mL volumetric flask, dilute with water to volume, and mix. Retain this solution for the
Limit of chloride and
Limit of sulfate tests. This solution responds to the test for
Magnesium 191.
B:
The retention times of the peaks corresponding to stearic acid and palmitic acid in the chromatogram of the Test solution correspond to those in the chromatogram of the System suitability solution, as obtained in the Relative content of stearic acid and palmitic acid test.
Microbial limits 61—
The total aerobic microbial count does not exceed 1000 cfu per g, the total combined molds and yeasts count does not exceed 500 cfu per g, and it meets the requirements of the tests for absence of
Salmonella species and
Escherichia coli.
Acidity or alkalinity—
Transfer 1.0 g to a 100-mL beaker, add 20 mL of carbon dioxide-free water, boil on a steam bath for 1 minute with continuous shaking, cool, and filter. Add 0.05 mL of
bromothymol blue TS to 10 mL of the filtrate: not more than 0.05 mL of 0.1 N hydrochloric acid or 0.1 N sodium hydroxide is required to change the color of the indicator.
Loss on drying 731—
Dry it at 105
to constant weight: it loses not more than 6.0% of its weight.
Specific surface area 846—
[NOTE—In cases where there are no functionality-related concerns regarding the specific surface area of this article, this test may be omitted.
] Where the labeling states the specific surface area, determine the specific surface area value as directed in the chapter in the
P/
P0 range of 0.05 to 0.15, and using outgassing conditions of 2 hours at 40
. If the plot deviates from linearity for
P/P0 values of 0.05 to 0.15, then a suitable range of
P/P0 values should be validated for linearity. In this case, it is necessary to state the range of validated
P/P0 values, the increment of the
P/P0 values, and the outgassing conditions employed.
Limit of chloride 221—
A 10.0-mL portion of the aqueous solution obtained in
Identification test
A shows no more chloride than corresponds to 1.4 mL of 0.020 N hydrochloric acid (0.1%).
Limit of sulfate 221—
A 3.0 mL portion of the aqueous solution obtained in
Identification test
A shows no more sulfate than corresponds to 3.0 mL of 0.020 N sulfuric acid (1.0%).
Lead 251—
Ignite 0.50 g in a silica crucible in a muffle furnace at 475
to 500
for 15 to 20 minutes. Cool, add 3 drops of nitric acid, evaporate over a low flame to dryness, and again ignite at 475
to 500
for 30 minutes. Dissolve the residue in 1 mL of a mixture of equal parts by volume of nitric acid and water, and wash into a separator with several successive portions of water. Add 3 mL of
Ammonium Citrate Solution and 0.5 mL of
Hydroxylamine Hydrochloride Solution, and render alkaline to phenol red TS with ammonium hydroxide. Add 10 mL of
Potassium Cyanide Solution. Immediately extract the solution with successive 5-mL portions of
Dithizone Extraction Solution, draining off each extract into another separator, until the last portion of dithizone solution retains its green color. Shake the combined extracts for 30 seconds with 20 mL of 0.2 N nitric acid, and discard the chloroform layer. Add to the acid solution 4.0 mL of
Ammonia-Cyanide Solution and 2 drops of
Hydroxylamine Hydrochloride Solution. Add 10.0 mL of
Standard Dithizone Solution, and shake the mixture for 30 seconds. Pass the chloroform layer through an acid-washed filter paper into a color-comparison tube, and compare the color with that of a standard solution prepared as follows. To 20 mL of 0.2 N nitric acid add 5 µg of lead, 4 mL of
Ammonia-Cyanide Solution, and 2 drops of
Hydroxylamine Hydrochloride Solution, and shake with 10.0 mL of
Standard Dithizone Solution for 30 seconds. Pass through an acid-washed filter paper into a color-comparison tube. The color of the sample solution does not exceed that of the control (0.001%).
Relative content of stearic acid and palmitic acid—
System suitability solution—
Transfer about 50 mg each of
USP Stearic Acid RS and
USP Palmitic Acid RS to a small conical flask fitted with a suitable reflux condenser. Add 5.0 mL of a solution prepared by dissolving 14 g of boron trifluoride in methanol to make 100 mL, swirl to mix, and reflux for 10 minutes until the solids have dissolved. Add 4 mL of chromatographic
n-heptane through the condenser, and reflux for 10 minutes. Cool, add 20 mL of saturated sodium chloride solution, shake, and allow the layers to separate. Pass the
n-heptane layer through 0.1 g of anhydrous sodium sulfate (previously washed with chromatographic
n-heptane) into a suitable flask. Transfer 1.0 mL of this solution to a 10-mL volumetric flask, dilute with chromatographic
n-heptane to volume, and mix.
Test solution—
Transfer about 100 mg of Magnesium Stearate, accurately weighed, to a small conical flask fitted with a suitable reflux condenser, and proceed as directed for System suitability solution, beginning with “Add 5.0 mL of a solution prepared by dissolving.”
Chromatographic system (see Chromatography 621)—
The gas chromatograph is equipped with a flame-ionization detector, maintained at about 260
; a splitless injection system; and a 0.32-mm × 30-m fused silica capillary column bonded with a 0.5-µm layer of phase G16. The column temperature is maintained at 70
for about 2 minutes after injection, then programmed to increase at the rate of 5
per minute to 240
and to maintain this temperature for 5 minutes. The injection port temperature is maintained at about 220
. The carrier gas is helium with a linear velocity of about 50 cm per second.
Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.86 for methyl palmitate and 1.0 for methyl stearate; the resolution, R, between the methyl palmitate and methyl stearate peaks is not less than 5.0; the relative standard deviation of the peak area responses for the palmitate and stearate peaks for replicate injections is not greater than 6.0%; and the relative standard deviation of the peak area response ratio of the palmitate to stearate peaks from these replicate injections is not more than 1.0%.
Procedure—
Inject about 1 µL of the
Test solution into the chromatograph, record the chromatogram, and measure the peak areas for all the fatty acid ester peaks in the chromatogram. Calculate the percentage of stearic acid in the fatty acid fraction of Magnesium Stearate taken by the formula:
100A/B,
in which
A is the area due to the methyl stearate peak, and
B is the sum of the areas of all the fatty acid ester peaks in the chromatogram. Similarly, calculate the percentage of palmitic acid in the portion of Magnesium Stearate taken. The stearate peak comprises not less than 40%; and the sum of the stearate and palmitate peaks is not less than 90% of the total area of all fatty acid ester peaks in the chromatogram.
Assay—
Ammonium chloride pH 10 buffer solution—
Dissolve 5.4 g of ammonium chloride in water, add 20 mL of ammonium hydroxide, and dilute with water to 100 mL.
Procedure—
Transfer about 500 mg of Magnesium Stearate, accurately weighed, to a 250-mL conical flask. Add 50 mL of a mixture of butyl alcohol and dehydrated alcohol (1:1), 5 mL of ammonium hydroxide, 3 mL of
Ammonium chloride pH 10 buffer solution, 30.0 mL of 0.1 M edetate disodium VS, and 1 or 2 drops of
eriochrome black TS, and mix. Heat at 45
to 50
until the solution is clear. Cool, and titrate the excess edetate disodium with 0.1 M zinc sulfate VS until the solution color changes from blue to violet (see
Titrimetry 541). Perform a blank determination, and make any necessary correction. Each mL of 0.1 M edetate disodium is equivalent to 2.431 mg of Mg.
