Spectroscopic identification of alizarin in a mixture of organic red dyes by incorporation in Zr-Ormosil



Raman and UV–visible spectroscopy were applied to the study of a mixture of alizarin and carminic acid, two highly fluorescent anthraquinone dyes. The selective incorporation of alizarin into a Zr-Ormosil polymer induced intense Raman spectra that allow an easy, quick and unequivocal identification of this dye. Therefore, this method can be applied to the separation and identification of dyes, which is an important issue in the field of archaeometry. Raman spectroscopy was used to identify alizarin in Zr-Ormosil at different pH values, solvents and dye concentrations. The best conditions for composite formation were determined. Moreover, the Raman spectra allow us to propose an interaction model for the alizarin–Zr complexes where the monoanionic alizarin forms a chelate with Zr cations in the doped Ormosil similar to the alizarin–Al chelate formed in lacs and alizarin–Ag chelate formed in SERS experiments. Copyright © 2005 John Wiley & Sons, Ltd.