Dental-Type Silica

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Dental-Type Silica is obtained from sodium silicate solution by destabilizing with acid in such a way as to yield very fine particles. The sum of the Assay values for Silicon Dioxide and Sodium Sulfate is NLT 98.0%.

2 ASSAY

2.1 SILICON DIOXIDE

Sample: 1 g

Analysis: Ignite the Sample at 1000° for 1 h, cool in a desiccator, and weigh. Carefully wet with water, and add 10 mL of hydrofluoric acid, in small increments. Evaporate on a steam bath to dryness, and cool. Add about 10 mL of hydrofluoric acid and about 0.5 mL of sulfuric acid, and evaporate to dryness. Slowly increase the temperature until all of the acids have been volatilized, and ignite at 1000°. Cool in a desiccator, and weigh. The difference between the final weight and the weight of the initially ignited portion represents the weight of SiO₂.

2.2 SODIUM SULFATE

Sample: 1 g

Analysis 1: In a platinum dish, wet the Sample with a few drops of water, add 15 mL of perchloric acid, and place the dish on a hot plate. Add 10 mL of hydrofluoric acid. Heat until copious fumes are evolved. Add 5 mL of hydrofluoric acid, and again heat to copious fumes. Add 5 mL of boric acid solution (1 in 25), and heat to fumes. Cool, and transfer the residue to a 400-mL beaker with the aid of 10 mL of hydrochloric acid. Adjust the volume with water to about 300 mL, and bring to boiling on a hot plate. Add 20 mL of hot barium chloride TS. Keep the beaker on the hot plate for 2 h, maintaining the volume above 200 mL. After cooling, transfer the precipitate and solution to a dried, tared crucible with a filter of 0.8-µm pore size. Wash the filter and precipitate 8 times with hot water, dry the crucible at 105° for 1 h, and weigh. The weight, multiplied by 0.6085, is the sodium sulfate content of the amount of specimen taken.

Acceptance criteria 1: NMT 4.0%

Analysis 2: Calculate the sum of the Assay values for the silicon dioxide and the sodium sulfate, and calculate the percentage in the Dental-Type Silica taken.

Acceptance criteria 2: NLT 98.0%

3 SPECIFIC TESTS

3.1 PH (791)

Sample solution: 50 mg/mL of slurry

Acceptance criteria: 4.0-8.5

3.2 LOSS ON DRYING (731)

Analysis: Dry a sample at 105° for 2 h.

Acceptance criteria: It loses NMT the maximum percentage of its weight as indicated in the labeling.

3.3 LOSS ON IGNITION (733)

Sample: 1 g, previously dried

Analysis: Ignite the Sample at 1000° for NLT 1 h.

Acceptance criteria: NMT 8.5%

3.4 CHLORIDE AND SULFATE, Chloride(221)

Sample solution: Boil 5 g in 50 mL of water under a reflux condenser for 2 h, cool, and filter.

Control: 1.0 mL of 0.020 N hydrochloric acid

Analysis: Use a 7-mL portion of Sample solution.

Acceptance criteria: 0.1%; the Sample solution shows no more chloride than the Control.

Change to read:

3.5 ARSENIC (211), Procedures, Procedure 1 (CN 1-JUN-2023)

Sample solution: Transfer 4.0 g of Dental-Type Silica to a platinum dish, add 5 mL of nitric acid and 35 mL of hydrofluoric acid, and evaporate on a steam bath. Cool, add 5 mL of perchloric acid, 10 mL of hydrofluoric acid, and 10 mL of sulfuric acid, and evaporate on a hot plate to the production of heavy fumes. Cool, cautiously transfer to a 100-mL beaker with the aid of a few mL of hydrochloric acid, and evaporate to dryness. Cool, add 5 mL of hydrochloric acid, dilute with water to about 40 mL, and heat to dissolve any residue. Cool, transfer to a 100-mL volumetric flask, and dilute with water to volume.

Analysis: Use a 25.0-mL portion of Sample solution.

Acceptance criteria: NMT 3 ppm

4 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers.

LABELING: Label it to indicate the maximum percentage of loss on drying.