Determination of uronic acids and neutral carbohydrates in pulp and biomass by hydrolysis, reductive amination and HPAEC-UV

Abstract

Abstract:The exact quantification of all carbohydrate constituents in wood and pulp is a challenge because of the various glycosidic linkages of the polysaccharides with different stabilities. The individual detector responses for the compounds in the hydrolysates additionally complicate the quantification as pure standards for 4-O-methyl-α-Dglucuronic acid (meGlcA) and related oligosaccharides are not commercially available for calibration. In the present paper, a new analytical procedure is presented, based on the reductive amination of the carbohydrates obtained via acidic and enzymatic hydrolysis of the polysaccharides before quantification by means of high performance anion exchange chromatography (HPAEC) and UV-detection. This approach was suitable for the analysis of neutral carbohydrates and uronic acids obtained via enzymatic hydrolysis from bleached pulps. In the case of unbleached pulps, the enzymatic hydrolysis was not complete and unhydrolyzed nano-scaled and microscaled particles remained in the hydrolysates as detected by dynamic light scattering (DLS) measurements. The new HPAEC-UV methodology was also applied to kraft pulps and a sulfite pulp; six different kinds of wood as well as wheat straw and bagasse. All relevant monosaccharides and the dimer of meGlcA and xylose could be detected in the hydrolysates. Accordingly, significantly higher yields of meGlcA were found compared to literature data.

Testing Clean-Up Methods for the Quantification of Monosaccharides and Uronic Acids

“…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 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 beetroot, 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.…”