The content of free formaldehyde as a preservative in water-based dispersion paints is commonly determined via the acetyl acetone method, recommended by the VdL-RL 03 directive. This method is well-known and established since 1953 by T. Nash. It is based on a chemical reaction of formaldehyde with acetyl acetone in the presence of ammonia to form a heterocyclic species, dihydro diacetyl lutidine (DDL), of yellow colour. Based on this colour, the amount of formaldehyde can be quantified by UV/VIS-spectroscopic measurements at 412 nm. However, for a single wavelength measurement this method relies on clear solutions. Difficulties arise when samples such as dispersion paints turn out to be turbid even after centrifugation, which in practice is more a rule than an exception. In such cases other techniques are recommended, however, for reasons of costs and convenience it would be better if with just one relatively simple spectroscopic method one could study samples regardless of the level of turbidity.
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