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

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-D-glucuronic 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 micro-scaled 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.