Overview
ISO 2227:1972 specifies a volumetric method for determining the formaldehyde (HCHO) content of industrial formaldehyde solutions. The procedure is applicable to solutions with 25–45% HCHO (field of application extendable by adjusting the test portion). The method is based on reaction of formaldehyde with a neutral sodium sulphite (sulfite) solution and an acidimetric titration of the liberated sodium hydroxide using thymolphthalein as the indicator. The standard also includes sampling, reagent and apparatus recommendations and safety warnings (formaldehyde is toxic; avoid inhalation).
Key topics and requirements
- Scope & applicability: Designed for industrial formaldehyde solutions between approximately 25% and 45% HCHO; extendable by modifying test portion mass.
- Principle: Formaldehyde reacts with neutral sodium sulphite; the liberated NaOH is titrated acidimetrically to an endpoint indicated by thymolphthalein.
- Reagents:
- Sodium sulphite solution (≈130 g/L) - prepared immediately before use.
- Sodium hydroxide, approximately 0.1 N.
- Hydrochloric acid standard volumetric solution, approximately 0.1 N.
- Thymolphthalein ethanolic indicator (2 g/L preparation).
- Apparatus: Ordinary laboratory glassware; a weighing pipette (~3 mL) for precise test portions.
- Procedure highlights:
- Weigh a small test portion (approx. 3 g) into water, neutralize and mix with reagents as specified.
- Combine test portion with neutralized sodium sulphite and titrate with standard HCl to the thymolphthalein endpoint.
- Mix and allow reactions to proceed for the prescribed time before titration.
- Expression of results: Formaldehyde content is calculated from the volume of HCl used and the mass of the test portion (expressed as percentage by mass).
- Sampling and sample condition: Method is valid for clear or slightly cloudy samples only; presence of precipitate (e.g., paraformaldehyde) invalidates results. Samples should be taken and tested promptly to avoid polymerization.
Applications and users
- Quality control laboratories in (formalin and formaldehyde producers).
