title: Optimization of sample treatment for the identification of anthraquinone dyes by surface-enhanced Raman spectroscopy.
abstract: The study and characterization of old artifacts such as pigments requires the use of techniques that need a small amount of sample to perform the analysis because of the high value of these samples. In recent years, organic molecules such as anthraquinone dyes have been identified by surface-enhanced Raman spectroscopy (SERS). However, different sample treatments must be applied to isolate the organic dye from the mordant, which produces great fluorescence in the Raman measurements. In this work, optimization of sample treatment for the SERS analysis of anthraquinone dyes was performed. Sample mass, the organic solvent, and its volume were optimized and different slide materials and excitation lasers were compared to choose the best conditions for the identification of the dyes. The optimization of sample treatment resulted in 5 mg of sample as the optimum amount. Further, two consecutive extractions with 0.5 mL of ethyl acetate was the best option for the extraction of the dye. A quartz slide was used instead of a glass slide to reduce background signal, and an excitation laser of 532 nm offers better results than one of 785 nm. The optimized method was applied to the characterization of the dyes used in Pompeian pink and purple lake pigments. Alizarin and purpurin anthraquinone dyes, obtained from madder lake, were identified as the organic colorants. The SERS results were confirmed by those obtained by means of UV-visible spectroscopy. Graphical Abstract ᅟ.
authors.affiliation: Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, 48080, Bilbao, Basque Country, Spain. iker.marcaida@ehu.eus.
authors.forename: Iker
authors.identifier: http://orcid.org/0000-0002-6258-2937
authors.initials: I
authors.lastname: Marcaida
authors.affiliation: Department of Analytical Chemistry, Faculty of Pharmacy, University of the Basque Country UPV/EHU, P.O. Box 450, 01080, Vitoria-Gasteiz, Basque Country, Spain.
authors.forename: Maite
authors.initials: M
authors.lastname: Maguregui
authors.affiliation: Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, 48080, Bilbao, Basque Country, Spain.
authors.forename: Héctor
authors.initials: H
authors.lastname: Morillas
authors.affiliation: Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, 48080, Bilbao, Basque Country, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: García-Florentino
authors.affiliation: Institute of Science and Technology in Art, Academy of Fine Arts, Schillerplatz 3, 1010, Vienna, Austria.
authors.forename: Valentina
authors.initials: V
authors.lastname: Pintus
authors.affiliation: Department of Chemistry, Faculty of Sciences, University of Chile, Santiago de Chile, Santiago, Chile.
authors.forename: Tomás
authors.initials: T
authors.lastname: Aguayo
authors.affiliation: Department of Chemistry, Faculty of Sciences, University of Chile, Santiago de Chile, Santiago, Chile.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Campos-Vallette
authors.affiliation: Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, 48080, Bilbao, Basque Country, Spain.
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Madariaga
keywords: Anthraquinone; Lake pigment; Liquid–liquid extraction; Madder lake; Surface-enhanced Raman spectroscopy