RAPID ULTRASOUND ASSISTED REDUCTION OF AZO DYES FOR SCREENING BANNED AROMATIC AMINES

Abstract

The screening of harmful colorants in consumer products is a global concern. The majority of textile and leather exports undergo extensive quality testing, consuming a lot of time and energy. Consequently, improvements in the rate of reduction of standard method for harmful azo dyes, EN 14362-1:2012 (Annex. F), by combining conventional heating with ultrasonication have been explored to adopt a greener approach. Basic dye behavior was investigated by UV-visible spectroscopy, so that more efficient reduction methods could be designed for high-tech instruments of analysis like HPLC with diode array detection (DAD) and GC with mass spectrophotometer (GC-MS). Four dyes were selected, namely Acid red 1 (AR-1), Direct blue 15 (DB-15), Direct red 28 (DR-28), and Direct red 7 (DR-7) containing one harmful aromatic amine in their structures which make them critical for analyses. Basic observation that absorbance of dyes (having azo chromospheres in their structure) decreases with their reduction to amines was exploited using UV-visible spectroscopic analysis with preselected absorption bands in the visible region from 400 to 700 nm. The dyes were subjected to two types of ultrasound assisted reduction (UAR) methods; less vigorous (experimental method 1) and more vigorous (experimental method 2). All dyes achieved reductions through ultrasonic assistance, higher than the reference method within ten min of time at or before 70 °C except DR-28, according to experimental method 1. According to experimental method 2, DB-15 and DR-7 achieved reductions equivalent to the reference method in 15 min of UAR at 70 °C whereas AR-1 and DR-28 achieved in 20 min of UAR. Finally, DR-28 was further subjected to experimental method 3, which was simply EN 14362-1:2012 (F) method for colorants, with UAR. At this stage, standard techniques of analysis exploiting HPLC-DAD and GC-MS were used. According to experimental method 3, even 15 min of UAR caused a greater reduction of DR-28 dye as compared to the standard method (BS EN 14362-1, F). Ultrasonication at 70°C reduced the total dye reduction time by 42% and energy consumption by 85%.