Dyeing textiles is much more complex and difficult than it appears at first glance. The colours should be easy to work with, stable against light and other environmental influences and not easily degradable. A long durability of the colours in the textiles is required. This catalogue of requirements is not easy to fulfil. The chemical nature of the dye used is decisive for its properties. For a long time, so-called azo dyes were used for dyeing textiles. These are so called because in all compounds within this group the molecule contains the azo functional group. Azo compounds can be degraded, which does often not happen during normal use, but only after a longer period of time. However, exposure to light or reductive stain removers facilitate the degradation and thus the release of the resulting fragments. Many of these fragments consist of so-called primary aromatic amines, almost all of which are classified as carcinogenic.
Legislators in the EU have restricted the use of azo dyes in textiles through the REACH regulation, which is why a marketability test should also include azo dyes. Because despite the ban, it is possible that these dyes are still used, either because the regulations are not as strict in other parts of the world, or because a small amount of a banned dye was used to refine the colour of the finished textile.
The test for amines from azo dyes is carried out according to DIN EN ISO 14362-1. The dyes and/or the amines are extracted and reduced in an aqueous citrate buffer. The amines are then dissolved in tert-butyl ether and passed over an SPE column. The amount of solvent is reduced and the concentration of the amines is determined.
There are some variables in this working process that can influence the result. The colours have to be extracted differently from different types of fibres. In addition, there are some amines that decompose further under the above conditions. To detect these, DIN EN ISO 14362-3 is used, which adjusts the pH differently during reduction to prevent further decomposition.