Degradation of food dyes by zero-valent metals exposed to ultrasonic irradiation in water medium: optimization and electrospray ionization mass spectrometry monitoring

• Published in: Journal of the Brazilian Chemical Society Vol. 22; no. 1; pp. 111 - 119
• Main Authors: Pavanelli, Sérgio P., Bispo, Glayson Leonardo, Nascentes, Clésia Cristina, Augusti, Rodinei
• Format: Journal Article
• Language: English
• Published: Sociedade Brasileira de Química 01-01-2011
• Subjects: CHEMISTRY, MULTIDISCIPLINARY; zero-valent metals; electrospray ionization mass spectrometry; food dyes; monitoring
• ISSN: 0103-5053; 1678-4790
• DOI: 10.1590/S0103-50532011000100015

The reductive degradation of four prototype dyes largely employed by the food industry (Brilliant Blue, Amaranth, Sunset Yellow and Red 40), by zero-valent metals (Fe and Sn) under ultrasonic irradiation in acidic aqueous solution (pH 3.0), was studied. The reactions were monitored by direct infusion ESI(-)-MS (electrospray ionization mass spectrometry in the negative ion mode) as well as by UV-Vis and total organic carbon (TOC). The influence of major parameters (time of exposure to ultrasonic irradiation and mass of metal) on the degradation rates was firmly established by means of factorial design and surface response approaches. Hence, it was noticed that, under the optimized experimental conditions, metallic iron (Fe) was able to efficiently degrade all the dyes (with rates higher than 90% after 30 min reaction time), whereas metallic tin (Sn) exhibited a noticeably lower performance. Low mineralization rates were achieved probably due to the essentially reductive character of such process. Based on the results from the ESI(-)-MS monitoring, a plausible degradation route for the Brilliant Blue dye in aqueous medium by the Fe/US system was proposed. Hence, this route involves, as initial pathways, the hydrogenation of the exocyclic carbon-carbon double bond of the dye followed by the insertion of hydride at its imino moiety.