4-[(2,5-dichlorophenyl)azo]-N-(2,3-dihydro-2-oxo-1H-benzimidazol-5-yl)-3-hydroxynaphthalene-2-carboxamide

Endpoint summary

Description of key information

For the hydrolysis endpoint an adaptation from the standard testing requirements relies upon the principle described in Annex XI-2. The study is technically  not possible due to the low water solubility of the substance and accompanying analytical complications. The water solubility of this pigment is determined to be 17 µg/L. The analytical method used for the determination of such low a concentration was based on the Lambert-Beer principle, in which the concentration of a solution is determined by means of the quantity of light that is absorbed upon passing through the solution via a path of known length.  It is however not possible to apply the same method for the analysis of samples from a hydrolysis study. The analytical determination of such samples would either require the determination of decreasing amounts of the parent substance, or of increasing amounts of its degradation products. For the current case, the parent substance has a large chromophore group (hence its application as a pigment), and any degradation products that could be formed from a theoretical point of view would still contain a substantial chromophore. As a consequence, the parent substance as well as its theoretical hydrolysis products would absorb light in the UV-VIS measurement – albeit with different extinction coefficients – which renders the Lambert-Beer equation unsolvable.  The development of other analytical techniques such as LC-MS, LC-UV-VIS etc. has also been considered. However, such techniques require the need for concentration of the hydrolysis samples. As the pigments have a low solubility not only in water but also in organic solvents, extraction protocols are not suitable for concentrating of the samples. As this renders all options for analytical determination of the substance and its degradation products unsuitable, the hydrolysis test is technically not possible.