Knowledge about carbohydrate composition of pulps and other cellulosic samples is essential for their characterization and further processing. The carbohydrate composition of cellulosic materials shows glucose as the predominant contributor coming from the cellulose itself, besides smaller amounts of pentoses, hexoses, and deoxy sugar from the hemicellulose fraction. Hydrolysis is necessary to cleave the glycosidic bonds of polysaccharides and determine the monosaccharide composition.

Strong hydrolysis, usually with sulfuric acid, leads to a release of reducing monosaccharides, but suffers from side reactions and other drawbacks. Methanolysis (Sundberg et al. 1996) represents a hydrolysis variant under mild conditions, the free monosaccharides are converted into their corresponding methyl glycosides, and the carboxyl groups of uronic acids are converted into methyl esters (Huang et al. 1992). The methyl glycosides formed by acid methanolysis lose their original anomeric configuration and equilibrate to a mixture of α- and ß-anomers (Laine et al. 2002). The compounds are determined by gas chromatography (GC) hyphenated to different detection modes (MS, FID), after suitable derivatization. The occurrence of up to four isomers after acid methanolysis reduces the risk of complete peak overlapping, and the constant ratio of isomers enables the possibility of compound identification and quantification in one single peak (Laine et al. 2002; Amelung et al. 1994).

The advantages of acid methanolysis compared to sulfuric acid hydrolysis are much less byproduct formation and the possibility to quantify uronic acids (Chambers et al. 1971). The main disadvantage is that cellulose is only partially hydrolyzed (mainly the amorphous regions) and hence no complete sugar profile with regard to the glucose/cellulose content can be obtained with methanolysis alone.

Sample amount generally required: 50-100 mg.

References

Sundberg, A.; Sundberg, K.; Lillandt, C.; Holmbom, B.,
Determination of hemicelluloses and pectins in wood and pulp fibres by acid methanolysis and gas chromatography.
Nordic Pulp and Paper Research Journal 1996, 11 (4), 216-219+226.

Huang, Y.; Indrarti, L.; Azuma, J.; Okamura, K.,
Simultaneous Determination of Xylose and Uronic-Acid in Beech Xylan by Methanolysis.
Mokuzai Gakkaishi 1992, 38 (12), 1168-1171.

Laine, C.; Tamminen, T.; Vikkula, A.; Vuorinen, T.,
Methylation analysis as a tool for structural analysis of wood polysaccharides.
Holzforschung 2002, 56 (6), 607-614.

Amelung, W.; Cheshire, M. V.; Guggenberger, G.,
Determination of neutral and acidic sugars in soil by capillary gas-liquid chromatography after trifluoroacetic acid hydrolysis.
Soil Biol Biochem 1996, 28 (12), 1631-1639.

Chambers, R. E.; Clamp, J. R.,
Assessment of Methanolysis and Other Factors Used in Analysis of Carbohydrate-Containing Materials.
Biochem J 1971, 125 (4), 1009.

Equipment for ion chromatography funded by IWB/EFRE-Program and REACT-EU funds