# Testing Clean-Up Methods for the Quantification of Monosaccharides and Uronic Acids
## 1 Introduction  
Carbohydrates are the most abundant compounds in nature. They are synthesized by green plants during photosynthesis and can be classified into two categories: simple and complex carbohydrates. Simple sugars, called monosaccharides, are carbohydrates that cannot be transformed into smaller molecules by hydrolysis contrarily to complex saccharides, commonly known also as oligosaccharides or polysaccharides, formed by hundreds or thousands of monosaccharide units. The determination and quantification of free monosaccharides and of saccharides constituting polysaccharides are of considerable importance in various fields. As regards the food industry, the determination of the glucose/fructose ratio in honey has allowed possible adulterations with sugars from cheaper sources such as corn, sugar can or beet to be sought out [1; 2; 3; 4]. Numerous studies are also devoted to the analysis of monosaccharides in vegetables [5; 6] and in confectionery products [7]. Attention has also been paid to the study of the antioxidant properties [8; 9] and immunomododulating effects [10] of monosaccharides in pharmaceuticals. Polysaccharide materials such as plant gums have also been widely employed since remote antiquity to produce artistic objects, e.g., used as binders for painting [11], in writing nks [12], in illuminated manuscripts [13], in portrait miniatures [14], and as adhesives in metal leaf decorations [15]. Therefore, thedetermination of monosaccharides in artistic samples after hydrolysis provides important information on the provenience, nature of the binder, and thus on the artistic technique. The quantitative analysis of mixtures of monosaccharides is highly challenging considering their structural similarity, and consequently their chemical one. Thus, chromatography constitutes the election method to separate and determine the content of single saccharides. High-Performance Liquid Chromatography (HPLC) has been efficiently employed thanks to the high solubility of these analytes in water [16, 17, 18], but also gas chromatography preceded by proper derivatization steps has been successfully used exploiting monosaccharides high polarity [19, 20]. The analysis of saccharide materials from a complex matrix often requires clean-up steps to eliminate interferences such as inorganic compounds [15]. Some inorganic materials seem to act as catalysts for the isomerization of some sugars, producing a modification of the quantitative and qualitative profiles of the saccharides [21]. Furthermore, their presence may adversely affect the analytical instrumentation, such as in the case of sulfates, which are detrimental for Anionic Exchange Liquid Chromatography (HPAEC) setups [22] and for mass spectrometric detectors, since the ionization efficiency is reduced and ionic suppression favored, affecting the detection of the analytes and the instrumentation maintenance [23]. The high level of inorganic ions may be contained in a wide variety of samples. Those from cultural heritage, as paint samples, represent a proper example considering that pigments, fillers, and additives of painting surfaces are rich in inorganic materials [24]. The analytical methods allowing the targeting and profiling of saccharides in oligosaccharides and in complex polysaccharides require their hydrolysis. A hydrolysis method commonly used involves the use of sulfuric acid [22], making the purification of the hydrolyzed sample mandatory in order to be injected into a chromatographic system. Another aspect to consider is that widely spread and exploited saccharide matrices, such as sugar cane and beet-root, contain further classes of compounds such as phenolic acids, flavonoids, and phenolic compounds (responsible for the antioxidant activity of the relative vegetable extracts [25]) that could affect the determination of saccharides.