Formaldehyde Solution

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Formalin

NOTE: The name Formalin as a synonym for Formaldehyde Solution may be used freely in many countries,including the United Kingdom, but in other countries exclusive proprietary rights in this name are claimed.

CH2O 30.03

Action and use Used in the treatment of warts.

DEFINITION

Formaldehyde solution (35 per cent) contains not less than 34.5 per cent m/m and not more than

38.0 per cent m/m of formaldehyde (CH2O; M r 30.03) with methanol as stabiliser.

CHARACTERS

A clear, colourless liquid, miscible with water and with alcohol. It may be cloudy after storage.

IDENTIFICATION

A. Dilute 1 ml of solution S (see Tests) to 10 ml with water R. To 0.05 ml of the solution add 1 ml of a 15 g / l solution of chromotropic acid, sodium salt R, 2 ml of water R and 8 ml of sulphuric acid R. A violet-blue or violet-red colour develops within 5 min.

B. To 0.1 ml of solution S add 10 ml of water R. Add 2 ml of a 10 g / l solution of phenylhydrazine

hydrochloride R, prepared immediately before use, 1 ml of potassium ferricyanide solution R and 5 ml of hydrochloric acid R. An intense red colour is formed.

C. Mix 0.5 ml with 2 ml of water R and 2 ml of silver nitrate solution R2 in a test-tube. Add dilute

ammonia R2 until slightly alkaline. Heat on a water-bath. A grey precipitate or a silver mirror is

formed.

D. It complies with the limits of the assay.

TESTS

Solution S Dilute 10 ml, filtered if necessary, to 50 ml with carbon dioxide-free water R.

Appearance of solution Solution S is colourless (Method II, 2.2.2).

Acidity To 10 ml of solution S add 1 ml of phenolphthalein solution R. Not more than 0.4 ml of 0.1M sodium hydroxide is required to change the colour of the indicator to red.

Methanol 9.0 per cent V/V to 15.0 per cent V/V, determined by gas chromatography (2.2.28) using

ethanol R1 as internal standard.

Internal standard solution. Dilute 10 ml of ethanol R1 to 100 ml with water R.

Test solution. To 10.0 ml of the solution to be examined add 10.0 ml of the internal standard solution and dilute to 100.0 ml with water R.

Reference solution. To 1.0 ml of methanol R add 10.0 ml of the internal standard solution and dilute to 100.0 ml with water R.

The chromatographic procedure may be carried out using:

— a glass column 1.5 m to 2.0 m long and 2 mm to 4 mm in internal diameter, packed with

ethylvinylbenzene-divinylbenzene copolymer R (150 μm to 180 μm),

— nitrogen for chromatography R as the carrier gas at a flow rate of 30 ml to 40 ml per minute,

— a flame-ionisation detector,

maintaining the temperature of the column at 120°C and that of the injection port and of the

detector at 150°C.

Inject 1 μl of the reference solution. Adjust the sensitivity of the detector so that the heights of the

peaks in the chromatogram obtained are not less than 50 per cent of the full scale of the recorder.

The test is not valid unless the resolution between the peaks corresponding to methanol and ethanol

is at least 2.0. Inject separately 1 μl of the test solution and 1 μl of the reference solution. Calculate

the percentage content of methanol.

Sulphated ash (2.4.14). Not more than 0.1 per cent, determined on 1.0 g.

ASSAY

Into a 100 ml volumetric flask containing 2.5 ml of water R and 1 ml of dilute sodium hydroxide

solution R, introduce 1.000 g of the solution to be examined, shake and dilute to 100.0 ml with

water R. To 10.0 ml of the solution add 30.0 ml of 0.05M iodine. Mix and add 10 ml of dilute sodium hydroxide solution R. After 15 min, add 25 ml of dilute sulphuric acid R and 2 ml of starch solution R.

Titrate with 0.1M sodium thiosulphate.

1 ml of 0.05M iodine is equivalent to 1.501 mg of CH2O.

STORAGE

Store in a well-closed container, protected from light, at a temperature of 15°C to 25°C.

Дата добавления: 2014-12-26