SiO2xH2O

Anhydrous 60.08

Packaging and storage— Preserve in tight containers,protected from moisture.

Labeling— Label it to state whether it is silica gel or precipitated silica.

Identification— Transfer about 5mg to a platinum crucible,mix with about 200mg of anhydrous potassium carbonate,ignite at a red heat over a burner for 10minutes,and cool.Dissolve the melt in 2mLof recently distilled water,warming if necessary,and slowly add 2mLof ammonium molybdate TS:a deep yellow color is produced.

pHá791ñ: between 4and 8,in a slurry (1in 20).

Loss on drying á731ñ— Dry it at 145for 4hours:it loses not more than 5.0%of its weight.

Loss on ignition á733ñ— Ignite about 1g of it,previously dried and accurately weighed,at 1000for not less than 1hour:it loses not more than 8.5%of its weight.

Chloride á221ñ— Boil 5g in 50mLof water under a reflux condenser for 2hours,cool,and filter.A7-mLportion of the filtrate shows no more chloride than corresponds to 1.0mLof 0.020Nhydrochloric acid (0.1%).

Sulfate á221ñ— A10-mLportion of the filtrate obtained in the test for Chlorideshows no more sulfate than corresponds to 5.0mLof 0.020Nsulfuric acid (0.5%).

Arsenic,Method Iá211ñ— Prepare the Test Preparationas follows.Transfer 4.0g to a platinum dish,add 5mLof nitric acid and 35mLof hydrofluoric acid,and evaporate on a steam bath.Cool,add 5mLof perchloric acid,10mLof hydrofluoric acid,and 10mLof sulfuric acid,and evaporate on a hot plate to the production of heavy fumes.Cool,cautiously transfer to a 100-mLbeaker with the aid of a few mLof hydrochloric acid,and evaporate to dryness.Cool,add 5mLof hydrochloric acid,dilute with water to about 40mL,and heat to dissolve any residue.Cool,transfer to a 100-mLvolumetric flask,dilute with water to volume,and mix.A25.0-mLportion of this solution meets the requirements of the test.The limit is 3ppm.

Heavy metals,Method Iá231ñ— Transfer 16.7mLof the solution prepared for the test for Arsenicinto a 100-mLbeaker,and neutralize with ammonium hydroxide to litmus paper.Adjust with 6Nacetic acid to a pHof between 3and 4.Filter,using medium-speed filter paper,wash with water until the filtrate and washings measure 40mL,and mix.The limit is 0.003%.

Organic volatile impurities,Method IVá467ñ: meets the requirements.

Assay— Transfer about 1g of Silica Gel to a tared platinum dish,ignite at 1000for 1hour,cool in a desiccator,and weigh.Carefully wet with water,and add about 10mLof hydrofluoric acid,in small increments.Evaporate on a steam bath to dryness,and cool.Add about 10mLof hydrofluoric acid and about 0.5mLof 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.

Expert Committee:(EMC)Excipients:Monograph Content

USP28–NF23Page 3073

Phone Number:1-301-816-8323