New Advances in Dye Analyses: In Situ Gel-Supported Liquid Extraction from Paint Layers and Textiles for SERS and HPLC-MS/MS Identification

To date, it is still not possible to obtain exhaustive information about organic materials in cultural heritage without sampling. Nonetheless, when studying unique objects with invaluable artistic or historical significance, preserving their integrity is a priority. In particular, organic dye identification is of significant interest for history and conservation research, but it is still hindered by analytes' low concentration and poor fastness. In this work, a minimally invasive approach for dye identification is presented. The procedure is designed to accompany noninvasive analyses of inorganic substances for comprehensive studies of complex cultural heritage matrices, in compliance with their soundness. Liquid extraction of madder, turmeric, and indigo dyes was performed directly from paint layers and textiles. The extraction was supported by hydrogels, which themselves can undergo multitechnique analyses in the place of samples. After extraction, Ag colloid pastes were applied on the gels for SERS analyses, allowing for the identification of the three dyes. For the HPLC-MS/MS analyses, re-extraction of the dyes was followed by a clean-up step that was successfully applied on madder and turmeric. The colour change perceptivity after extraction was measured with colorimetry. The results showed & UDelta;E values mostly below the upper limit of rigorous colour change, confirming the gentleness of the procedure.

Automated summary

This study presents a minimally invasive approach for dye identification, allowing for research on cultural heritage without compromising its integrity. Liquid extraction of madder, turmeric, and indigo dyes directly from paint layers and textiles is performed, supported by hydrogels. Various techniques, such as SERS and HPLC-MS/MS, are applied for dye identification. Color change perceptivity measurements confirm the gentleness of the procedure, protecting the cultural heritage.