(Ph. Eur. monograph 0434)
SiO2 60.1 7631-86-9
Action and use
Excipient.
DEFINITION
Content
99.0 per cent to 100.5 per cent of SiO2 (ignited substance).
CHARACTERS
Appearance
White or almost white, light, fine, amorphous powder, with a particle size of about 15 nm.
Solubility
Practically insoluble in water and in mineral acids except hydrofluoric acid. It dissolves in hot solutions of alkali hydroxides.
IDENTIFICATION
About 20 mg gives the reaction of silicates (2.3.1).
TESTS
pH (2.2.3)
3.5 to 5.5.
Shake 1.0 g with 30 mL of carbon dioxide-free water R.
Chlorides (2.4.4)
Maximum 250 ppm.
To 1.0 g add a mixture of 20 mL of dilute nitric acid R and 30 mL of water R and heat on a water-bath for 15 min, shaking frequently. Dilute to 50 mL with water R if necessary, filter and cool. Dilute 10 mL of the filtrate to 15 mL with water R.
Loss on ignition
Maximum 5.0 per cent, determined on 0.200 g by ignition in a platinum crucible at 900 ± 50 °C for 2 h. Allow to cool in a desiccator before weighing.
ASSAY
To the residue obtained in the test for loss on ignition add 0.2 mL of sulfuric acid R and sufficient ethanol (96 per cent) R to moisten the residue completely. Add 6 mL of hydrofluoric acid R and evaporate to dryness on a hot-plate at 95-105 °C, taking care to avoid loss from sputtering. Wash down the sides of the dish with 6 mL of hydrofluoric acid R and evaporate to dryness. Ignite at 900 ± 50 °C, allow to cool in a desiccator and
weigh.
The difference between the mass of the final residue and the mass of the residue obtained in the test for loss on ignition gives the amount of SiO2 in the quantity of the substance to be examined used.
FUNCTIONALITY-RELATED CHARACTERISTICS
This section provides information on characteristics that are recognised as being relevant control parameters for one or more functions of the substance when used as an excipient (see chapter 5.15). Some of the characteristics described in the Functionality-related characteristics section may also be present in the mandatory part of the monograph since they also represent mandatory quality criteria. In such cases, a cross-reference to the tests described in the mandatory part is included in the Functionality-related characteristics section. Control of the characteristics can contribute to the quality of a medicinal product by improving the consistency of the manufacturing process and the performance of the medicinal product during use. Where control methods are cited, they are recognised as being suitable for the purpose, but other methods can also be used. Wherever results for a particular characteristic are reported, the control method must be indicated.
The following characteristic may be relevant for colloidal anhydrous silica used as glidant in tablets and capsules.
Specific surface area (2.9.26, Method I)
Determine the specific surface area in the P/P0 range of 0.05 to 0.30.
Sample outgassing: 20 min at 160 °C.
