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Purified Siliceous Earth(选自USP38-NF33 SECOND SUPPLEMENT)
DEFINITION
Purified Siliceous Earth is a form of silica (SiO2 ) consisting of the frustules and fragments of diatoms, purified by calcining.
IMPURITIES
• Loss on Ignition 733Sample: 1 g, previously dried
Analysis: Ignite the Sample at 980 ± 25 for 1 h in a tared platinum or porcelain crucible.
Acceptance criteria: NMT 2.0%
• Leachable ArsenicSample solution: To 10.0 g in a 250-mL beaker add 50 mL of 0.5 N hydrochloric acid, cover with a watch glass, and heat at 70 for 15 min. 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, and dilute with water to volume.
Analysis: A 3.0-mL portion of the Sample solution meets the requirements in Arsenic, Method 1 211.
Acceptance criteria: NMT 10 μg/g
• Leachable LeadSample: A 10.0-mL portion of the Sample solution prepared in the test for Leachable Arsenic
Control: 10 mL of Diluted Standard Lead Solution in Lead 251
Analysis: The Sample meets the requirements in Lead 251.
Acceptance criteria: NMT 10 μg/g
• Limit of Nonsiliceous SubstancesSample: 200 mg
Analysis: Transfer the Sample 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.
Acceptance criteria: The weight of the residue is NMT 50 mg.
SPECIFIC TESTS
• Loss on Drying 731Analysis: Dry a sample at 105 for 2 h.
Acceptance criteria: NMT 0.5%
• Acid-Soluble SubstancesSample: 10.0 g
Analysis: Digest the Sample with 50 mL of 0.5 N hydrochloric acid at 70 for 15 min, 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.
Acceptance criteria: NMT 2.0% (weight of the dried residue is NMT 200 mg)
• Water-Soluble SubstancesSample: 12.5 g
Analysis: Place the Sample in a 500-mL conical flask, add 250 mL of water, and shake for 2 h 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.
Acceptance criteria: NMT 0.2% (weight of the residue is NMT 25 mg)
ADDITIONAL REQUIREMENTS
• Packaging and Storage: Preserve in well-closed containers.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
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USP38–NF33 Page 6862
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