Electrochemical identification of flavonoid dyes in solid work of art samples by abrasive voltammetry at paraffin-impregnated graphite electrodes

An electrochemical method for identifying flavonoid-type dyes in microsamples from works of art is reported. Square wave voltammograms of natural insoluble dyestuffs based on flavonoid structure dragoon's blood, weld, old fustic, gamboge, Brazilwood and logwood (Campeche wood) attached to paraffin-impregnated graphite electrodes in contact with 0.25 M HAc + 0.25 M NaAc aqueous buffer display characteristic peaks in the potential region between +0.85 and −0.85 V versus AgCl/Ag. Sequential experiments in contact with 0.05 M AlCl₃ and 0.05 M Na₂MoO₄ plus HAc/NaAc and 0.05 M H₃BO₃ + 0.10 M NaOH solutions also provide dye-characteristic signals allowing for an unambiguous identification of each one of the pigments. Individual pigments were satisfactorily identified in mixtures of pigments and real samples from textile pieces found in Castellfort (Valencian Region, Spain) attributed to the 15th century production of local textile workshops.