Plant gums have been used in a variety of applications such as in food emulsifiers, stabilisers, and thickeners, pharmaceuticals, cosmetics, textiles, and in art. Plant gums have been used for centuries as binding media, to paint, write and illuminate manuscripts and to apply metallic leaf decorations
. Gums and other kind of saccharide materials, such as honey, fig milk or starch, are known to have been used as binding media, sizing agents or mummification materials since antiquity. Actually, carbohydrates are contained in a variety of materials used as support, binders and varnishes in painted objects
. Wood and paper are common paint supports, and carbohydrates, both free and bound, can be encountered as minor fractions in a variety of paint materials, such as proteinaceous binders, as well as plant and animal terpenoid resins.
GC-MS analytical techniques are routinely used to determine the sugar composition of polysaccharide materials, and are among the best suited for the identification of natural organic materials used in the field of Cultural Heritage. GC-MS is a sensitive technique and highly suitable for the analysis of natural organic substances when the resolution and determination of the molecular profile is essential in order to identify the materials present and the ageing pathways
. In general the GC-MS analysis of polysaccharide materials requires a chemolysis step, followed by derivatisation
[4, 5]. Moreover the analysis of saccharide materials in paint samples needs an additional step of purification, in order to remove pigments and fillers. There are many different chemolysis procedures used to study plant gums
, based on: the methanolysis
[7, 8], on the hydrolysis
[9–13], and hydrolysis assisted by microwaves of the polysaccharide
[14–16]. Rates of degradation differ for each monosaccharide during hydrolysis. The sugars are released in the order of ease of bond fission: furanosidic > pyranosidic,6-deoxyhexosidic > hexosidic > and neutral hexosidic > uronosidic
. Hydrolysis is complicated if there are proteins or polyphenols in the gum sample, and therefore interaction with the reducing sugars may take place. If the polysaccharide has a limited solubility, this also increases the difficulties. Derivatisation is fundamental in the GC-MS analysis of saccharides, due to the high number of polar moieties present in each molecule
[4, 18, 19]. Thermally assisted hydrolysis and methylation
 and on-line pyrolysis/silylation
[21, 22] can also be used, but the interpretation of the data in samples from Cultural Heritage is more complex and needs further investigation. Most sugars in saccharide materials used in the field of Cultural Heritage occur as three types: aldoses (e.g. glucose), ketoses (e.g. fructose), or uronic acids (e.g. glucuronic acid). It is very difficult to analyze all three types of sugars in one quantitative analysis without creating multiple derivatives of each sugar
. To avoid the formation of multiple derivatives, which occur because sugars have different isomeric forms in solution
, various derivatisation procedures have been proposed, such as the reduction of carbonyl moieties followed by acetylation
[25, 26] the conversion of monosaccharides into acyclic oximes, followed by silylation
 or acetylation
[9, 10], or the formation of diethyl mercaptal derivatives followed by silylation
[13, 27]. Each of these methodologies has its own advantages and drawbacks
, but none of them is able to derivatise aldoses, ketoses and uronic acids at the same time without inducing any degradation, or producing chromatograms too complex to be unequivocally interpreted.
Because of these inherent difficulties, those analyzing carbohydrates in the field of cultural heritage are not able to fully compare data obtained from a variety of different analytical methodologies, because each of them produce extremely different chromatographic profiles and multiple databases
[13, 28, 29]. Moreover, in most cases the results of the quantitative analyses are not given, so that evaluating the sugar profiles of the paint samples are even more complex.
In this paper we present a comparison between two different analytical procedures that have been independently developed, optimised and systematically used to characterise plant gums in samples collected from works of art
[22, 27, 29–34]. The research was carried out independently at two laboratories: the Getty Conservation Institute in Los Angeles, USA (GCI) and the Department of Chemistry and Industrial Chemistry of the University of Pisa, Italy (DCCI). The GCI procedure is based on the methoxylamine acetate derivatisation of neutral sugars (aldoses and ketoses) obtained from saccharide materials after hydrolysis. The DCCI procedure is based on the analysis of the mercaptal derivatives of the parent aldoses and uronic acids obtained after hydrolysis assisted by microwaves. Both procedures are used to quantitatively determine the sugar profile obtained by each polysaccharide gum after chemolysis. The data obtained with the two procedures are compared in order to understand if the chromatographic profiles are influenced by the analytical protocols and are affected differently by the sample composition. Given the proven homogeneity of the data obtained with the two techniques, a common database of sugar profiles of organic materials which can be encountered in paint samples, has been developed and is presented here.