Abstract

The four azo dyes Acid Red I (C. 1. 18050), Acid Black I (C. I. 20470). Acid Black 234 (C. 1. 30027) and Direct Black 168 (C. I. 30410) were analysed to calculate the amount of 4-aminodiphenyl (ADP) present after sodium dithionite reduction of the azo groups. This method follows the description in DIN 53 316. Synthesised and non-purified dyes showed high contamination, whereas the TLC cleaned Acid Black I (C. I. 20470) revealed no ADP in measurable amounts.