Aluminum Monostearate
(a loo' mi num mon'' oh steer' ate).

Aluminum, dihydroxy(octadecanoato-O-)-.
Dihydroxy(stearato)aluminum [7047-84-9].
» Aluminum Monostearate is a compound of aluminum with a mixture of solid organic acids obtained from fats, and consists chiefly of variable proportions of aluminum monostearate and aluminum monopalmitate. It contains the equivalent of not less than 14.5 percent and not more than 16.5 percent of Al2O3, calculated on the dried basis.
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 for 1 hour, replacing the water as it evaporates: fatty acids are liberated, floating as an oily layer on the surface of the liquid, and the water layer responds to the tests for Aluminum 191.
B: Mix intimately 25 g with 100 mL of ether in a 500-mL flask, add 150 mL of 3 N hydrochloric acid, attach a water-cooled condenser, and heat on a steam bath under reflux for 15 minutes. Cool, and transfer both layers to a separator with the aid of an additional 100 mL of ether. Shake vigorously, and allow the layers to separate. Remove the water layer, and wash the ether layer with three 30-mL portions of water. Transfer the ether layer to a small beaker, warm on a steam bath until the ether has evaporated and the fatty acids are clear, and dry the acids at 105 for 20 minutes: the solidification temperature (see Fats and Fixed Oils 401) of the fatty acids is not below 54.
Loss on drying 731 Dry it at 80 for 16 hours: it loses not more than 2.0% of its weight.
Arsenic, Method I 211 Prepare the Test Preparation as follows. To 3.75 g add 12.5 mL of hydrochloric acid and 0.5 mL of bromine TS, and heat on a steam bath until a transparent layer of melted fatty acid forms. Add 50 mL of water, heat on a hot plate until the volume is about 25 mL, and filter while hot. Cool, dilute the filtrate with water to 50 mL, and to a 10-mL aliquot of this solution add 2.5 mL of hydrochloric acid, then 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 for Procedure being omitted. The limit is 4 ppm.
Heavy metals— To 2 g contained in a 250-mL flask add 20 mL of water and 10 mL of hydrochloric acid. Place a small funnel in the neck of the flask, and boil gently, replacing the water as it evaporates, until the fatty acids separate in a clear layer. Cool rapidly by rotating under a stream of cold water until the fatty acids solidify. Decant through a filter previously washed with 3 N hydrochloric acid, wash until the combined filtrate and washings measure 50 mL, and mix. To 20 mL of the pooled filtrate add 6 N ammonium hydroxide, dropwise, until a permanent turbidity forms. Add 1 N acetic acid until the precipitate just dissolves, then add 2 mL in excess, and add water to make 40 mL. Add 1.2 mL of thioacetamide-glycerin base TS and 2 mL of pH 3.5 Acetate Buffer, and allow to stand for 5 minutes: any brown color produced is not darker than that of a control solution prepared from 10 mL of the pooled filtrate and 2 mL of Standard Lead Solution (see Heavy Metals 231) containing 10 µg of lead per mL, then diluted with water to 20 mL and treated in the same manner. The limit is 50 µg per g.
Assay— Accurately weigh 5 g of Aluminum Monostearate in a covered platinum crucible that previously has been ignited for 20 minutes, cooled over anhydrous magnesium perchlorate, and weighed. Heat the open crucible gently, without allowing the specimen to burst into flame, and gradually increase the heat until the ash is white. Ignite the ash for 20 minutes after the organic matter is removed, and cool. Add 15 mL of water, cover the crucible with a small watch glass, and boil gently for 5 minutes, using a small stirring rod to break up any large lumps of ash. Decant the solution through ashless filter paper, retaining most of the ash in the crucible. Repeat the extraction with water twice, passing the solutions through the same filter. Transfer the ash to the filter by means of a fine stream of water, and wash the crucible and the residue three times with warm water. Transfer the filter paper and the residue to the crucible, dry, and ignite for 20 minutes after the filter paper has burned away. Following the ignition period, cover the crucible, cool over anhydrous magnesium perchlorate for 15 minutes, and weigh the residue of Al2O3 rapidly. Repeat the ignition until constant weight is attained, using 20-minute ignition periods and 15-minute cooling periods. From the weight of the residue remaining in the crucible, calculate the content of Al2O3.
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Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, M.S.
Scientific Liaison
(EXC2010) Monographs - Excipients
USP35–NF30 Page 1693