FL 15 - A Quasi-Non-Invasive Sampling Strategy Combined with MALDI-MS and RPLC-ESI-MS for the Analysis and Identification of Gums as Ancient Painting Binders

Elena C. L. Rigante, Cosima D. Calvano, Tommaso R. I. Cataldi

Dipartimento di Chimica, Università degli Studi di Bari Aldo Moro, 70126 Bari, Italy

Natural gums have long been used as painting binders to disperse pigments on various substrates, including wood, murals, and parchments. Composed mainly of polysaccharides, these materials strongly influence the physical and chemical properties of artworks; therefore, their accurate characterization is essential for conservation and restoration purposes. Recent advances in mass spectrometry (MS), particularly with soft ionization techniques such as matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI), have enabled detailed molecular profiling of these complex materials [1]. However, conventional sampling procedures are often invasive and unsuitable for fragile or valuable heritage objects, as they require the removal of small portions of the painting film.

To overcome these limitations, we developed a quasi-non-invasive in-situ sampling protocol based on enzyme-loaded hydrogels [2,3] for the analysis of polysaccharide binders. High-retention hydrogels functionalized with endo-1,4-β-mannanase [4] act as micro-extractors when applied to the artwork surface. During contact, the enzyme digests the gum binder into oligosaccharides, which are subsequently recovered and identified by MALDI-MS and/or RPLC-ESI-MS. A dedicated chromatographic method using a C18 column was optimized to separate the derivatized oligosaccharides using iodomethane. The protocol was first validated on standard monosaccharides and pure gums digested in solution and tested on painting mock-ups prepared with gum–pigment mixtures on parchment and non-cellulosic paper substrates. These experiments confirmed the main advantage of the method, a traceless, minimally invasive sampling procedure, and demonstrated its strong potential for cultural heritage diagnostics, particularly when traditional sampling would risk damaging fragile or precious artworks.

Acknowledgements: This work was supported by Progetto di Ricerca di Interesse Nazionale—PRIN 2022CNNRWZ- REActive GEl for orgaNic bindERs recognition in Artworks (REAGENERA), financed by the Unione Europea- Next Generation EU- Missione 4 componente 1 CUP H53D23003830006.

Keywords: natural gums, in situ digestion, RPLC-ESI-MS/MS 

References

1. Geddes da Filicaia E., Evershed R., et al., Analytica Chimica Acta, 1246 (2023), pag. 340575, 10.1016/j.aca.2022.340575

2. Calvano C. D., Rigante E. C. L., et al., Talanta, 215 (2020), pag. 120882, 10.1016/j.talanta.2020.120882

3. Calvano C. D., Rigante E. C. L., et al., Analytical Chemistry, 92 (2020), pagg. 10257-10261 10.1021/acs.analchem.0c01898.

4. Granzotto C., Arslanoglu J., et al., Scientific Reports, 7, (2017), pagg 1-15, 10.1038/srep44538.