Matrix Assisted Laser Desorption Ionization Mass Fingerprinting for Identification of Acacia Gum in Microsamples from Works of Art

Abstract

This paper reports an improved method for the identification of Acacia gum in cultural heritage samples using matrix assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) after enzymatic digestion of the polysaccharide component. The analytical strategy was optimized using a reference Acacia gum (gum arabic, sp. A. senegal) and provided an unambiguous MS profile of the gum, characterized by specific and recognized oligosaccharides, from as little as 0.1 μg of material. The enhanced experimental approach with reduced detection limit was successfully applied to the analysis of naturally aged (∼80 year) gum arabic samples, pure and mixed with lead white pigment, and allowed the detection of gum arabic in samples from a late painting (1949/1954) by Georges Braque in the collection of the Art Institute of Chicago. This first application of the technique to characterize microsamples from a painting, in conjunction with analyses by gas chromatography/mass spectrometry (GC/MS), provided important insights into Braque's unusual mixed paint media that are also helpful to inform appropriate conservation treatments for his works. The robustness of the analytical strategy due to the reproducibility of the gum MS profile, even in the presence of other organic and inorganic components, together with the minimal sample size required, demonstrate the value of this new MALDI-TOF MS method as an analytical tool for the identification of gum arabic in microsamples from museum artifacts.

New insight from MALDI-TOF MS and multivariate data analysis on the botanical origin of polysaccharide-based paint binders in ancient Egypt

“…The MALDI-TOF mass ngerprints of S. senegal and Vachellia seyal gums have already been shown and fully discussed in previous works (reported as A. senegal and A. seyal). 24,26 Further experiments to investigate the possible inuence of pigments on the obtained spectra were subsequently carried out using S. senegal gum combined with various pigments, and these did not provide evidence for signicant interference in the examples tested, supporting the reliability of the analytical strategy when dealing with historic paint samples (ESI Fig. S1 and S2 †).…”

“…A successful approach to overcome the limitations of the monosaccharide-based analysis has been achieved by moving from a complete hydrolysis of the polysaccharide, to a partial enzymatic digestion using specic glycoside hydrolases followed by analysis of the released oligosaccharides by matrix assisted laser desorption ionization-time-of-ight mass spectrometry (MALDI-TOF MS). This analytical strategy has proved effective in discriminating among the most known plant genera mentioned above, 23 in the presence of other organic and inorganic compounds and in aged micro samples from historical works of art, 24,25 with the additional advantage of distinguishing gums from individual Acacia species such as A. senegal and A. seyal. 26 The present work is focused on the expansion of the previously built database of MALDI-MS spectra generated from reference samples of acacieae gums, 26 which now represents 19 different acacieae species, for a total of 56 samples, as well as mass spectral interpretation to understand the chemical nature of individual gums and the application of principal component analysis (PCA) to aid in grouping of the samples.…”

“…A successful approach to overcome the limitations of the monosaccharide-based analysis has been achieved by moving from a complete hydrolysis of the polysaccharide, to a partial enzymatic digestion using specific glycoside hydrolases followed by analysis of the released oligosaccharides by matrix assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). This analytical strategy has proved effective in discriminating among the most known plant genera mentioned above, 23 in the presence of other organic and inorganic compounds and in aged micro samples from historical works of art, 24,25 with the additional advantage of distinguishing gums from individual Acacia species such as A. senegal and A. seyal . 26…”

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for 2017–2018

“…Similar methods have been used to identify acacia gum in microsamples (0.1 μg) taken from works of art. The analytical strategy successfully applied to the analysis of naturally aged (~80 year) gum arabic samples, pure and mixed with lead white pigment, and allowed the detection of gum arabic in samples from a late painting (1949/1954) by Georges Braque (1882‐1963) in the collection of the Art Institute of Chicago (Granzotto & Sutherland, 2017).…”

Chapter 9. Chromatography

“…Gum arabic as little as 100ng, has been enzyme digested with exo-β-1,3-galactanase in a phosphate buffer for MALDI-MS and derivatised for MALDI-TOF MS with 3-aminoquinoline in aqueous solvent. It was found that minute amounts of sample needed less enzyme and digestion times to improve the MS response, with the advantage of digestion directly on the sample to minimise loss and for reproducible enzyme hydrolysis profiles (Granzotto & Sutherland, 2017).…”