title: A novel methylation derivatization method for δ(18)O analysis of individual carbohydrates by gas chromatography/pyrolysis-isotope ratio mass spectrometry.
abstract: BACKGROUND
  The oxygen isotope ratio (δ(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, δ(18)O analyses are often performed on carbohydrate bulk material, while compound-specific δ(18)O analyses remain challenging and methods for a wide range of individual carbohydrates are rare.
  
  
  METHODS
  To improve the δ(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 1.09‰ for the δ(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 δ(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 δ(18)O analysis of various individual carbohydrates; it is fast and easy-to-handle, and may therefore find wide-spread application.
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, PSI, CH-5232, Villigen, Switzerland.
authors.forename: Marco M
authors.initials: MM
authors.lastname: Lehmann
authors.affiliation: Laboratory of Nanoscale Materials Science, Empa, Überlandstrasse 129, CH-8600, Dübendorf, Switzerland.
authors.forename: Maria
authors.initials: M
authors.lastname: Fischer
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, PSI, CH-5232, Villigen, Switzerland.
authors.forename: Jan
authors.initials: J
authors.lastname: Blees
authors.affiliation: Department of Soil Biogeochemistry, Martin-Luther-University Halle Wittenberg, Von-Seckendorff-Platz 3, D-06120, Halle, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Zech
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, PSI, CH-5232, Villigen, Switzerland.
authors.forename: Rolf T W
authors.initials: RT
authors.lastname: Siegwolf
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, PSI, CH-5232, Villigen, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Saurer
mesh_terms: D002241:Carbohydrates / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006722:Honey / Q000032:analysis; D008745:Methylation; D010103:Oxygen Isotopes / Q000032:analysis*; D010936:Plant Extracts / Q000737:chemistry; D015203:Reproducibility of Results
chemical_list: D002241:Carbohydrates; D010103:Oxygen Isotopes; D010936:Plant Extracts