Aluminum Oxide, Acid-Washed
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
(Alumina specially prepared for use in chromatographic analysis) CAS RN: 1344-28-1.-White or practically white powder or fine granules. Very hygroscopic. Store in tight containers.
pH of Slurry: The pH of a well-mixed slurry of 5 g in 150 mL of ammonia-free and carbon dioxide-free water, after 10 minutes' standing, is between 3.5 and 4.5.
Loss on Ignition: Weigh accurately about 1 g, and ignite, preferably in a muffle furnace at 800° to 825°, to constant weight: it loses not more than 5.0% of its weight.
Silica: Fuse 500 mg with 10 g of potassium bisulfate for 1 hour in a platinum crucible, cool, and dissolve in hot water: not more than a small amount of insoluble matter remains.
Suitability for Chromatographic Adsorption: Dissolve 50 mg of o-nitroaniline in benzene to make 50.0 mL. Dilute 10 mL of the resulting solution with benzene to 100.0 mL, and mix (Solution A).
Weigh quickly about 2 (±0.005) g of specimen in a glass-stoppered weighing bottle, and rapidly transfer it to a dry, glass-stoppered test tube.
Add 20.0 mL of Solution A, insert the stopper, shake vigorously for 3 minutes, and allow to settle.
Pipet 10 mL of the clear supernatant into a 100-mL volumetric flask, dilute with benzene to volume, and mix (Solution B).
Determine the absorbances of Solutions A and B at 395 nm, with a suitable spectrophotometer, using benzene as the blank. Calculate the quantity, in mg, adsorbed per g of test specimen by the formula:
[2(1 − AB /AA )]/W
in which AA and AB are the absorbances of Solutions A and B, respectively; and W is the weight, in g, of the aluminum oxide. Not less than 0.3 mg of o-nitroaniline is adsorbed for each g of the aluminum oxide.
