Silicon Dioxide [14464-46-1] 

This product is prepared by reacting sodium silicate with acid or salts to produce silicic acid precipitate (i.e., hydrated silicon dioxide), which is then washed with water to remove impurities and dried. Calculated on the ignited basis, it contains not less than 99.0% of SiO?. 

[Description] This product is a white, loose powder; odorless and tasteless.

Salt: Take 10 ml of the continuous filtrate from the chloride test, examine as directed (General Rule 0801)[1], and compare with a control solution prepared from 5.0 ml of standard potassium solution. The color should not be deeper (0.5%). 

Loss on drying: Dry the sample at 145°C for 2 hours; the loss in weight should not exceed 5.0% (General Rule 0831).

Loss on ignition  Take 1.0 g of the sample remaining from the loss on drying test, accurately weighed, and ignite at 1000°C for 1 hour; the loss in weight should not exceed 8.5% of the dried sample weight.   

Iron salts  Take 0.2 g of the sample, add 25 ml of water, 2 ml of hydrochloric acid, and 5 drops of nitric acid, boil for 5 minutes, cool, filter, wash the filter with a small amount of water, combine the filtrate and washings, add 50 mg of ammonium persulfate, dilute with water to 35 ml, examine as directed (General Rule 0807), and compare with a control solution prepared from 3.0 ml of standard iron solution. The color should not be deeper (0.015%).

Heavy metals  Take 3.3 g of the sample, add 40 ml of water and 5 ml of hydrochloric acid, heat gently and boil for 15 minutes, cool, filter, transfer the filtrate to a 100 ml volumetric flask, wash the filter with an appropriate amount of water, combine the washings into the flask, dilute with water to the mark, mix well, take 20 ml, add 1 drop of phenolphthalein indicator solution, titrate with ammonia test solution until a faint red color appears, add 2 ml of acetate buffer (pH 3.5 ) and sufficient water to make 25 ml, examine as directed (General Rule 0821, Method I); the content of heavy metals should not exceed 30 parts per million. Arsenic salt  Take 20 ml of the solution from the heavy metals test, examine as directed (General Rule 0822, Method I); it should comply with the requirement (0.0003% ).

[Assay] Take 1 g of the sample, accurately weighed, place in a platinum crucible that has been ignited to constant weight at 1000°C, ignite at 1000°C for 1 hour, remove, cool, accurately weigh, moisten the residue with water, add 10 ml of hydrofluoric acid dropwise, evaporate to dryness on a water bath, cool, continue to add 10 ml of hydrofluoric acid and 0.5 ml of sulfuric acid, evaporate to near dryness on a water bath, transfer to an electric furnace and heat gently until the acid fumes are completely removed, ignite at 1000°C to constant weight, cool, accurately weigh; the loss in weight is the weight of SiO? in the sample.

[Category] Pharmaceutical excipient, glidant and suspending agent, etc.

[Storage] Preserve in a tightly closed container.