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Glycerol

Glycerin

C3H8O3 92.1

Action and useLubricant; laxative.

Glycerol Suppositories

DEFINITION

Glycerol contains not less than 98.0 per cent and not more than the equivalent of 101.0 per cent of

propane-1,2,3-triol, calculated with reference to the anhydrous substance.

CHARACTERS

A syrupy liquid, unctuous to the touch, colourless or almost colourless, clear, very hygroscopic,

miscible with water and with alcohol, slightly soluble in acetone, practically insoluble in ether, in fatty oils and in essential oils.

IDENTIFICATION

First identification: A, B.

Second identification: A, C, D.

A. It complies with the test for refractive index (see Tests).

B. To 5 ml add 1 ml of water R and mix carefully. Examine the solution by infrared absorption

spectrophotometry (2.2.24), comparing with the Ph. Eur. reference spectrum of glycerol (85 per cent).

C. Mix 1 ml with 0.5 ml of nitric acid R. Superimpose 0.5 ml of potassium dichromate solution R. A blue ring develops at the interface of the liquids. Within 10 min, the blue colour does not diffuse into the lower layer.

D. Heat 1 ml with 2 g of potassium hydrogen sulphate R in an evaporating dish. Vapours (acrolein) are volved which blacken filter paper impregnated with alkaline potassium tetraiodomercurate solution R.

TESTS

Solution SDilute 100.0 g to 200.0 ml with carbon dioxide-free water R.

Appearance of solutionSolution S is clear (2.2.1). Dilute 10 ml of solution S to 25 ml with

water R. The solution is colourless (Method II, 2.2.2).

Acidity or alkalinityTo 50 ml of solution S add 0.5 ml of phenolphthalein solution R. The solution is colourless. Not more than 0.2 ml of 0.1M sodium hydroxide is required to change the colour of the indicator to pink.

Refractive index(2.2.6). 1.470 to 1.475.

AldehydesPlace 7.5 ml of solution S in a ground-glass-stoppered flask and add 7.5 ml of water R

and 1.0 ml of decolorised pararosaniline solution R. Close the flask and allow to stand for 1 h at a

temperature of 25 ± 1°C. The absorbance of the solution measured at 552 nm (2.2.25) is not greater

than that of a standard prepared at the same time and in the same manner using 7.5 ml of

formaldehyde standard solution (5 ppm CH2O) R and 7.5 ml of water R. The test is not valid unless the standard is pink.

EstersAdd 0.1M sodium hydroxide to the final solution obtained in the test for acidity or alkalinity

until a total of 10.0 ml has been added. Boil under a reflux condenser for 5 min. Cool. Add 0.5 ml of phenolphthalein solution R and titrate with 0.1M hydrochloric acid. Not less than 8.0 ml of 0.1M hydrochloric acid is required to change the colour of the indicator.

Impurity A and related substancesExamine by gas chromatography (2.2.28).

Test solution. Dilute 10.0 ml of solution S to 100.0 ml with water R.

Reference solution (a). Dissolve 1.000 g of diethylene glycol R in water R and dilute to 100.0 ml with the same solvent.

Reference solution (b). Dilute 1.0 ml of reference solution (a) to 10.0 ml with the test solution. Dilute 1.0 ml of this solution to 20.0 ml with the test solution.

Reference solution (c). Mix 1.0 ml of the test solution and 5.0 ml of reference solution (a) and dilute

to 100.0 ml with water R. Dilute 1.0 ml of this solution to 10.0 ml with water R.

Reference solution (d). Dilute 5.0 ml of reference solution (a) to 100.0 ml with water R.

The chromatographic procedure may be carried out using:

— a fused-silica column 30 m long and 0.53 mm in internal diameter coated with a mixture of

cross-linked polycyanopropylphenylsiloxane (6 per cent) and polydimethylsiloxane (94 per cent)

(film thickness 3 μm),

helium for chromatography R as the carrier gas at a linear velocity of about 38 cm/s and with a split ratio of about 10:1,

— a flame-ionisation detector,

maintaining the temperature of the column at 100°C until injection, then raising the temperature at a

rate of 7.5°C per minute to 220°C and maintaining at 220°C for 4 min; maintaining the temperature

of the injection port at 220°C and that of the detector at 250°C.

Inject 0.5 μl of the reference solution (c). Adjust the sensitivity of the system such that the height of

the peak due to impurity A is at least 50 per cent of the full scale of the recorder. When the chromatograms are recorded in the prescribed conditions, the substances are eluted in the following order: impurity A and glycerol.

The test is not valid unless: in the chromatogram obtained with reference solution (c), the

resolution between the peaks corresponding to impurity A and to glycerol is at least 7.0.

Inject 0.5 μl of the test solution, 0.5 μl of reference solution (b) and 0.5 μl of reference solution (d).

In the chromatogram obtained with the test solution: the area of any peak corresponding to impurity

A is not greater than half the area of the corresponding peak in the chromatogram obtained with

reference solution (b) (0.1 per cent); the area of any peak, apart from the peak corresponding to

impurity A, and with a retention time less than the retention time of glycerol, is not greater than half

the area of the peak corresponding to impurity A in the chromatogram obtained with reference

solution (b) (0.1 per cent); the sum of the areas of any peaks with retention times greater than the

retention time of glycerol, is not greater than 2.5 times the area of the peak corresponding to impurity

A in the chromatogram obtained with reference solution (b) (0.5 per cent). Disregard any peak with

an area less than 0.05 times the area of the peak corresponding to impurity A in the chromatogram

obtained with reference solution (d).

Halogenated compoundsTo 10 ml of solution S add 1 ml of dilute sodium hydroxide solution R,

5 ml of water R and 50 mg of halogen-free nickel-aluminium alloy R. Heat on a water-bath for 10 min, allow to cool and filter. Rinse the flask and the filter with water R until 25 ml of filtrate is obtained.

To 5 ml of the filtrate add 4 ml of alcohol R, 2.5 ml of water R, 0.5 ml of nitric acid R and 0.05 ml of silver nitrate solution R2 and mix. Allow to stand for 2 min. Any opalescence in the solution is not more intense than that in a standard prepared at the same time by mixing 7.0 ml of chloride standard solution (5 ppm Cl) R, 4 ml of alcohol R, 0.5 ml of water R, 0.5 ml of nitric acid R and 0.05 ml of silver nitrate solution R2 (35 ppm).

SugarsTo 10 ml of solution S add 1 ml of dilute sulphuric acid R and heat on a water-bath for 5 min. Add 3 ml of carbonate-free dilute sodium hydroxide solution R (prepared by the method described for carbonate-free 1M sodium hydroxide (4.2.2), mix and add dropwise 1 ml of freshly prepared copper sulphate solution R. The solution is clear and blue. Continue heating on the water-bath for 5 min. The solution remains blue and no precipitate is formed.

Chlorides(2.4.4). 1 ml of solution S diluted to 15 ml with water R complies with the limit test for

chlorides (10 ppm). Prepare the standard using 1 ml of chloride standard solution (5 ppm Cl) R diluted to 15 ml with water R.

Heavy metals(2.4.8). Dilute 8 ml of solution S to 20 ml with water R. 12 ml of the solution

complies with limit test A for heavy metals (5 ppm). Prepare the standard using lead standard solution (1 ppm Pb) R.

Water(2.5.12). Not more than 2.0 per cent, determined on 1.500 g by the semi-micro determination of water.

Sulphated ash(2.4.14). Not more than 0.01 per cent, determined on 5.0 g after heating to boiling

and ignition.

ASSAY

Thoroughly mix 0.1000 g with 45 ml of water R. Add 25.0 ml of a 21.4 g/l solution of

sodium periodate R. Allow to stand protected from light for 15 min. Add 5.0 ml of a 500 g/l solution of ethylene glycol R and allow to stand protected from light for 20 min. Using 0.5 ml of phenolphthalein solution R as indicator, titrate with 0.1M sodium hydroxide. Carry out a blank titration. 1 ml of 0.1M sodium hydroxide is equivalent to 9.21 mg of C3H8O3.

STORAGE

Store in an airtight container.


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