Spectroscopic and chromatographic analysis of yellow flavonoidic lakes: Quercetin chromophore

To better understand the interactions between organic (natural flavonol) and inorganic (alum) constituents of Stil de grain, yellow lake model compounds based on quercetin as a chromophore were prepared and compared in terms of color and stability with those of historical, reconstituted samples. The extraction process of the natural dyes was optimized by varying the quantity of Rhamnus berries, the solvent, the temperature, the time and the extraction method in order to evaluate the role of the natural dye composition on the lake properties. The samples (chromophores and their AI(III) complexes embedded in an aluminum hydroxide matrix) were characterized by high performance liquid chromatography-photodiode array (HPLC-PDA). UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS). The conditions of preparation (solvent, temperature, time, extraction method) were correlated to physico-chemical features. Extraction of quercetin from the lake was optimized by using acetic acid buffer and ultrasound. This procedure will enable an improved analysis to be made of current historical materials. (C) 2011 Elsevier B.V. All rights reserved.