Formaldehyde Solution BP

Formalin
Formaldehyde Solution (35 per cent), Ph Eur
CH2O -- 30.03 -- 50-00-0
Action and use: When suitably diluted, used in the treatment of warts.

DEFINITION
Content: 34.5 per cent m/m to 38.0 per cent m/m of formaldehyde (CH2O; Mr 30.03). It contains methanol as stabiliser.

CHARACTERS
Appearance: Clear, colourless liquid.
Solubility: Miscible with water and with ethanol (96 per cent). It may be cloudy after storage.

IDENTIFICATION
A. Dilute 1 ml of solution S (see Tests) to 10 ml with water. To 0.05 ml of the solution add 1 ml of a 15 g/l solution of chromotropic acid sodium salt, 2 ml of water and 8 ml of sulphuric acid. A violet-blue or violet-red colour develops within 5 min.
B. To 0.1 ml of solution S add 10 ml of water. Add 2 ml of a 10 g/l solution of phenylhydrazine hydrochloride, prepared immediately before use, 1 ml of potassium ferricyanide solution and 5 ml of hydrochloric acid. An intense red colour is formed.
C. Mix 0.5 ml with 2 ml of water and 2 ml of silver nitrate solution  in a test-tube. Add dilute ammonia 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.
Appearance of solution: Solution S is colourless.
Acidity: To 10 ml of solution S add 1 ml of PhPh solution. Not more than 0.4 ml of 0.1 M sodium hydroxide is required to change the colour of the indicator to red.
Methanol: To pass Gas chromatography.
Sulphated ash: Maximum 0.1 per cent, determined on 1.0 g.

ASSAY
Into a 100 ml volumetric flask containing 2.5 ml of water and 1 ml of dilute sodium hydroxide solution, introduce 1.000 g of the solution to be examined, shake and dilute to 100.0 ml with water. To 10.0 ml of the solution add 30.0 ml of 0.05 M iodine. Mix and add 10 ml of dilute sodium hydroxide solution. After 15 min, add 25 ml of dilute sulphuric acid and 2 ml of starch solution. Titrate with 0.1 M sodium thiosulphate.
1 ml of 0.05 M iodine is equivalent to 1.501 mg of CH2O.

Formaldehyde Solution USP

CH2O 30.03
Formaldehyde [50-00-0].
Formaldehyde Solution in bulk containers contains not less than 37.0 percent, by weight, of formaldehyde (CH2O), with methanol added to prevent polymerization. Formaldehyde Solution in small containers (4 liters or less) contains not less than 36.5 percent, by weight, of formaldehyde (CH2O), with methanol present to prevent polymerization.

Packaging and storage: Preserve in tight containers, and preferably store at a temperature not below 15C.
Labeling: The label of bulk containers of the Solution directs the drug repackager to demonstrate compliance with the USP Assay limit for formaldehyde of not less than 37.0%, by weight, immediately prior to repackaging.

Identification:
A: Dilute 2 mL with 10 mL of water in a test tube, and add 1 mL of silver-ammonia-nitrate: metallic silver is produced either in the form of a finely divided, gray precipitate, or as a bright, metallic mirror on the sides of the test tube.
B: Add 2 drops to 5 mL of sulfuric acid in which about 20 mg of salicylic acid has been dissolved, and warm the liquid very gently: a permanent, deep-red color appears.

Acidity: Measure 20.0 mL into a flask containing 20 mL of water, add 2 drops of bromothymol blue and titrate with 0.1 N sodium hydroxide: not more than 10.0 mL of 0.1 N sodium hydroxide is consumed.
Assay: Transfer about 3 mL of Solution to a tared flask containing 10 mL of water, insert the stopper in the flask tightly, and accurately determine the weight of the Solution taken. Slowly and quantitatively add a mixture of 50.0 mL of 1 N sodium hydroxide and 50 mL of hydrogen peroxide that has been previously neutralized to bromothymol blue with 1 N sodium hydroxide. Heat the contents of the flask cautiously on a steam bath for 15 minutes, shaking it occasionally with a rotary motion. Allow the mixture to cool, rinse the funnel and the inner wall of the flask with water, and after allowing it to stand for 30 minutes, add 2 to 5 drops of bromothymol blue and titrate the excess alkali with 1 N sulfuric acid. Perform a blank determination (see Residual Titrations under Titrimetry). Also make a correction based upon the acidity found in the test for Acidity. Each mL of 1 N sodium hydroxide is equivalent to 30.03 mg of CH2O.