0434e

Silica, colloidal anhydrous EUROPEAN PHARMACOPOEIA 5.0

there is a light blue zone (shellolic acid) accompanied byzones of the same colour but of lower intensity. Otherfaint grey and violet zones may be visible.

B. Examine the chromatograms obtained in the testfor colophony. For wax-containing shellac, in thechromatogram obtained with the test solution, a moreor less strong bluish-grey zone is visible, just abovethe zone due to thymolphthalein in the chromatogramobtained with the reference solution. For dewaxedshellac, no such zone is visible just above the zone dueto thymolphthalein in the chromatogram obtained withthe reference solution.

TESTS

Colophony. Examine by thin-layer chromatography (2.2.27),as described under identification test A with the followingmodifications.

Test solution. Dissolve 50 mg of the powdered substance(500), while heating, in a mixture of 0.5 ml of methylenechloride R and 0.5 ml of methanol R.

Reference solution. Dissolve 2.0 mg of thymolphthalein Rin 1.0 ml of methanol R.

Examine the plate in ultraviolet light at 254 nm. Mark thequenching zones in the chromatogram obtained with the testsolution that have similar Rf values to that of the quenchingzone of thymolphthalein in the chromatogram obtainedwith the reference solution. Spray with anisaldehydesolution R, heat the plate at 100 °C to 105 °C for 5 minto 10 min and examine in daylight. The chromatogramobtained with the reference solution shows a principal zonewith a reddish- violet colour (thymolphthalein). None ofthe quenching zones in the chromatogram obtained withthe test solution that have an Rf value similar to the zonedue to thymolphthalein in the reference solution show amore or less strong violet or brownish colour (colophony).Disregard any faint violet zone at this level that does notshow quenching before spraying and heating.

Acid value (2.5.1) : 65 to 95, calculated with reference tothe dried substance. Examine 1.00 g of the coarsely groundsubstance. Determine the end-point by potentiometry(2.2.20).

Arsenic (2.4.2). Introduce 0.33 g of the substance to beexamined and 5 ml of sulphuric acid R into a combustionflask. Carefully add a few millilitres of strong hydrogenperoxide solution R and heat to boiling until a clear,colourless solution is obtained. Continue heating toeliminate the water and as much sulphuric acid as possibleand dilute to 25 ml with water R. The solution complies withlimit test A for arsenic (3 ppm).

Heavy metals (2.4.8). 2.0 g complies with limit test D forheavy metals (10 ppm). Prepare the standard using 2 ml oflead standard solution (10 ppm Pb) R.

Loss on drying (2.2.32). Not more than 2.0 per cent forunbleached shellac and not more than 6.0 per cent forbleached shellac, determined on 1.000 g of the powderedsubstance (500) by drying in an oven at 40 °C to 45 °C for24 h.

STORAGE

Store protected from light. Store bleached shellac andbleached, dewaxed shellac at a temperature not exceeding15 °C.

LABELLING

The label indicates the type of shellac.

01/2005:0434

SILICA, COLLOIDAL ANHYDROUS

Silica colloidalis anhydrica

SiO2 Mr 60.1

DEFINITION

Colloidal anhydrous silica contains not less than 99.0 percent and not more than the equivalent of 100.5 per cent ofSiO2, determined on the ignited substance.

CHARACTERS

A light, fine, white, amorphous powder, with a particle sizeof about 15 nm, practically insoluble in water and in mineralacids except hydrofluoric acid. It dissolves in hot solutionsof alkali hydroxides.

IDENTIFICATION

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

TESTS

pH (2.2.3). Shake 1.0 g with 30 ml of carbon dioxide-freewater R. The pH of the suspension is 3.5 to 5.5.

Chlorides (2.4.4). To 1.0 g add a mixture of 20 ml of dilutenitric acid R and 30 ml of water R and heat on a water-bathfor 15 min, shaking frequently. Dilute to 50 ml with water Rif necessary, filter and cool. 10 ml of the filtrate diluted to15 ml with water R complies with the limit test for chlorides(250 ppm).

Heavy metals (2.4.8). Suspend 2.5 g in sufficient water R toproduce a semi-fluid slurry. Dry at 140 °C. When the driedsubstance is white, break up the mass with a glass rod. Add25 ml of 1 M hydrochloric acid and boil gently for 5 min,stirring frequently with the glass rod. Centrifuge for 20 minand filter the supernatant liquid through a membrane filter.To the residue in the centrifuge tube add 3 ml of dilutehydrochloric acid R and 9 ml of water R and boil. Centrifugefor 20 min and filter the supernatant liquid through the samemembrane filter. Wash the residue with small quantities ofwater R, combine the filtrates and washings and dilute to50 ml with water R. To 20 ml of the solution add 50 mgof ascorbic acid R and 1 ml of concentrated ammonia R.Neutralise with dilute ammonia R2. Dilute to 25 ml withwater R. 12 ml of the solution complies with limit test A forheavy metals (25 ppm). Prepare the standard using leadstandard solution (1 ppm Pb) R.

Loss on ignition. Not more than 5.0 per cent, determined on0.200 g by ignition in a platinum crucible at 900 °C for 2 h.Allow to cool in a desiccator before weighing.

ASSAY

To the residue obtained in the test for loss on ignitionadd 0.2 ml of sulphuric acid R and sufficient alcohol R tomoisten the residue completely. Add 6 ml of hydrofluoricacid R and evaporate to dryness on a hot-plate at 95 °Cto 105 °C, taking care to avoid loss from sputtering. Washdown the sides of the dish with 6 ml of hydrofluoric acid Rand evaporate to dryness. Ignite at 900 °C, allow to cool in adesiccator and weigh.

The difference between the mass of the final residue and themass of the residue obtained in the test for loss on ignitiongives the amount of SiO2 in the quantity of the substanceto be examined used.

2410 See the information section on general monographs (cover pages)