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Procedure for determination of free formaldehyde concentration according to VdL-Guideline 03

Posted Date:2025/12/2

6.1. Acetyl acetone method

(Determination of free formaldehyde concentration)

A sample of (2.5 ± 0.3) g of water-dilutable paint or varnish (note initial sample weight to nearest 0.001 g) is weighed into a graduated 25 ml cylinder, to which 10 ml of acetyl acetone reagent is added before being filled up to 25 ml with deionised water and shaken. After 2 h at room temperature, the supernatant is transferred with a pipette to a centrifuge tube, the tube screwed shut and then centrifuged for approx. 20 min at 22000 rpm. If no clear serum is produced at this speed, a centrifuge capable of 30000 rpm or alternatively Centrisart I tubes (Sartorius brand, max. 4300 rpm for 20 min) (or a comparable product) must be used instead. After centrifuging is complete, the clear supernatant is transferred to the measurement cuvette. If turbidity occurs, the supernatant can be filtered with a syringe through a 0.2 µm single-use filter (for example) before being transferred to the cuvette.

In parallel, a blank solution is also prepared by pipetting 10 ml of acetone reagent into a graduated cylinder, which is filled up to 25 ml with deionised water and then shaken. The hold time for the solution until measurement is 2 h at room temperature.

Both solutions are measured against one another at 412 nm in the spectrophotometer.

Working range:

At formaldehyde concentrations over 100 mg/kg, the diacetyl dihydrolutidine begins to crystallise and turbidity occurs. In this case, select a smaller initial sample weight for the paint or varnish. 

Depending on the photometer used, determination limits of up to 0.1 mg/kg are achieved. The limit of determination must be determined individually. It must be ensured that the value expected is within the working range of the method.

Note:

In accordance with the standard procedure from VdL Guideline 03, samples are prepared using water. If no clear supernatant is obtained after the centrifugation step, the photometric determination may contain a systematic error as a result of turbidity. In this case, some other suitable solvent (e.g. methanol) can be used.

Since the free formaldehyde is in equilibrium with the bound formaldehyde and the equilibrium can further be influenced by the solvent, this means that the free formaldehyde content determined in water may differ to that determined in some other solvent.

This change in solvent must be documented in the test report and the result for free

formaldehyde with the different solvent must be reported.

The samples and the blank solution must always be prepared using the same solvent!

If a solvent other than water is selected, a calibration curve must be created for formaldehyde in this solvent.