Vibrational characterization of E102 food additive by Raman and surface‐enhanced Raman spectroscopy and theoretical studies

Abstract

Abstract The well‐known food dye E102 could be detected in aqueous solutions by means of regular Raman and surface‐enhanced Raman scattering (SERS) spectroscopy at micromolar and nanomolar levels, respectively. The changes observed in the profile of the band at 1365 cm −1 , characteristic of the ν(NN) mode of the azo chromophore group, allowed us to establish the present species in the Raman and SERS solutions at different concentrations or pH values. Protonation at the azo group of the molecule was detected for acidic pH values <3. In the pH range 3–8, no changes in the molecular species were observed. Density functional theory (DFT)‐calculated geometries, harmonic vibrational modes and Raman scattering activities for E102 were in good agreement with the experimental data, a complete vibrational assignment being proposed. A strong chemical interaction of E102 with colloidal particles was evidenced and an adsorbed geometry was proposed. Copyright © 2005 John Wiley & Sons, Ltd.