Direct gel-supported liquid extraction from paint layers: a new invisible procedure for SERS and HPLC-HRMS identification of dyes in complex matrices

The study of dyes employed in artworks is of big interest for history and conservation research, but the most critical aspect in such matter is the necessity of sampling. Dyes are easy to fade and usually low in concentration compared to inorganic components, thus, their signals in mixtures can be easily covered during non-invasive analyses. With the rise of SERS supports for minimally invasive analyses of dyes, more and more attention has been given to hydrogels. Hydrogels are substances able to hold more than 90% of water (v/v) in their three-dimensional network, showing a solid-fluid dualism [1]. This property makes them able to absorb aqueous solutions and release them in a controlled way. Besides their employment in surface cleaning [2], during the last decades it became clear hydrogels loaded with appropriate solutions could be used for direct dyes extraction from cultural heritage, for SERS identification [3]. The presented work was aimed at challenging the direct gel-supported liquid extraction (GSLE) to multi-technique dyes identification from complex paint matrices.