Colloidal Anhydrous Silica

(Ph. Eur. monograph 0434)

SiO₂    60.1    7631-86-9

Excipient.

Ph Eur

99.0 per cent to 100.5 per cent of SiO₂ (ignited substance).

White or almost white, light, fine, amorphous powder, with a particle size of about 15 nm.

Practically insoluble in water and in mineral acids except hydrofluoric acid. It dissolves in hot solutions of alkali hydroxides.

About 20 mg gives the reaction of silicates (2.3.1).

3.5 to 5.5.

Shake 1.0 g with 30 mL of carbon dioxide-free water R.

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.

Maximum 25 ppm.

Suspend 2.5 g in sufficient water R to produce a semi-fluid slurry. Dry at 140 °C. When the dried substance is white, break up the mass with a glass rod. Add 25 mL of 1 M hydrochloric acid and boil gently for 5 min, stirring frequently with the glass rod. Centrifuge for 20 min and filter the supernatant liquid through a membrane filter. To the residue in the centrifuge tube add 3 mL of dilute hydrochloric acid R and 9 mL of water R and boil. Centrifuge for 20 min and filter the supernatant liquid through the same membrane filter. Wash the residue with small quantities of water R, combine the filtrates and washings and dilute to 50 mL with water R. To 20 mL of the solution add 50 mg of ascorbic acid R and 1 mL of concentrated ammonia R. Neutralise with dilute ammonia R2. Dilute to 25 mL with water R. 12 mL of the solution complies with test A. Prepare the reference solution using lead standard solution (1 ppm Pb) R.

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.

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.

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 ). This section is a non-mandatory part of the monograph and it is not necessary to verify the characteristics to demonstrate compliance. Control of these characteristics can however 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.

Determine the specific surface area in the P/P₀ range of 0.05 to 0.30.

Sample outgassing  20 min at 160 °C.

Ph Eur