Determination of hemicelluloses and pectins in wood and pulp fibres by acid methanolysis and gas chromatography

An analytical method for quantitative determination of wood hemicelluloses and pectins in pulp fibres or wood meal was developed. Pulp fibres or wood meal were freeze-dried and submitted to acid methanolysis with HCl in anhydrous methanol. The resulting sugar units were silylated and their amount and composition determined by gas chromatography. The method gives the amounts of neutral as well as acidic sugar units in non-cellulosic polysaccharides. Only very small sample amounts (10 mg) are needed. The results obtained are in good agreement with data reported in the literature and the repeatability is good. Cellulose is only slightly degraded by acidic methanolysis, meaning that most of the glucose formed is derived from non-cellulosic polysaccharides. Galacturonic acid was found to be the predominant acidic sugar unit in spruce, pine and birch wood as well as in spruce and aspen mechanical pulps. Glucomannans which were adsorbed onto TMP fibres after deacetylation were not completely degraded by acid methanolysis.