A novel methylation derivatization method for delta super(18)O analysis of individual carbohydrates by gas chromatography/pyrolysis-isotope ratio mass spectrometry

• Published in: Rapid communications in mass spectrometry Vol. 30; no. 1; pp. 221 - 229
• Main Authors: Lehmann, Marco M, Fischer, Maria, Blees, Jan, Zech, Michael, Siegwolf, Rolf TW, Saurer, Matthias
• Format: Journal Article
• Language: English
• Published: 01.01.2016
• Subjects: Carbohydrates; Catalysts; Dimethyl; Gas chromatography; Mass spectrometry; Methylation; Silver oxides; Soils
• ISSN: 0951-4198; 1097-0231
• DOI: 10.1002/rcm.7431

Rationale The oxygen isotope ratio ( delta super(18)O) of carbohydrates derived from animals, plants, sediments, and soils provides important information about biochemical and physiological processes, past environmental conditions, and geographical origins, which are otherwise not available. Nowadays, delta super(18)O analyses are often performed on carbohydrate bulk material, while compound-specific delta super(18)O analyses remain challenging and methods for a wide range of individual carbohydrates are rare. Methods To improve the delta super(18)O analysis of individual carbohydrates by gas chromatography/pyrolysis-isotope ratio mass spectrometry (GC/Pyr-IRMS) we developed a new methylation derivatization method. Carbohydrates were fully methylated within 24 h in an easy-to-handle one-pot reaction in acetonitrile, using silver oxide as proton acceptor, methyl iodide as methyl group carrier, and dimethyl sulfide as catalyst. Results The precision of the method ranged between 0.12 and 1.09ppt for the delta super(18)O values of various individual carbohydrates of different classes (mono-, di-, and trisaccharides, alditols), with an accuracy of a similar order of magnitude, despite high variation in peak areas. Based on the delta super(18)O values of the main isomers, important monosaccharides such as glucose and fructose could also be precisely analyzed for the first time. We tested the method on standard mixtures, honey samples, and leaf carbohydrates extracted from Pinus sylvestris, showing that the method is also applicable to different carbohydrate mixtures. Conclusions The new methylation method shows unrivalled accuracy and precision for delta super(18)O analysis of various individual carbohydrates; it is fast and easy-to-handle, and may therefore find wide-spread application.