Packaging and storage— Preserve in well-closed containers.

Loss on drying 731— Dry it at 105 for 2 hours: it loses not more than 0.5% of its weight.

Loss on ignition 733— Transfer about 1 g, previously dried and accurately weighed, to a tared platinum or porcelain crucible, and ignite at 980 ± 25 for 1 hour: it loses not more than 2.0% of its weight.

Acid-soluble substances— Digest 10.0 g with 50 mL of 0.5 N hydrochloric acid at 70 for 15 minutes, and filter. Wash the residue, adding the washings to the filtrate, to obtain a total volume of 100 mL. Evaporate at 110 in a tared porcelain dish to dryness: the weight of the dried residue so obtained does not exceed 200 mg (2.0%).

Water-soluble substances— Place 12.5 g in a 500-mL conical flask, add 250 mL of water, and shake for 2 hours at room temperature. Filter with the aid of vacuum, and again filter if necessary to obtain a clear filtrate. Evaporate in a tared platinum or porcelain dish, and dry at 110: the weight of the residue does not exceed 25 mg (0.2%).

Leachable arsenic— Transfer 10.0 g to a 250-mL beaker, add 50 mL of 0.5 N hydrochloric acid, cover with a watch glass, and heat at 70 for 15 minutes. Cool, and decant through a Whatman No. 3 filter paper into a 100-mL volumetric flask. Wash the slurry with three 10-mL portions of water, preheated to 70, dilute with water to volume, and mix: a 3.0-mL portion of this solution meets the requirements under Arsenic, Method I 211. The limit is 0.001%.

Leachable lead— A 10.0-mL portion of the solution prepared in the test for Leachable arsenic meets the requirements under Lead 251, 10 mL of Diluted Standard Lead Solution being used for the control. The limit is 0.001%.

Limit of nonsiliceous substances— Transfer about 200 mg, accurately weighed, to a tared platinum crucible, add 5 mL of hydrofluoric acid and 2 drops of dilute sulfuric acid (1 in 2), and evaporate gently to dryness. Cool, add 5 mL of hydrofluoric acid, evaporate again to dryness, and ignite to constant weight: the weight of the residue so obtained does not exceed 50 mg.

Topic/Question	Contact	Expert Committee
Monograph	Hong Wang, Ph.D. Scientist 1-301-816-8351	(EM205) Excipient Monographs 2

USP32–NF27 Page 1337

PURIFIED SILICEOUS EARTH

Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.