A novel methylation derivatization method for δ¹⁸O analysis of individual carbohydrates by gas chromatography/pyrolysis–isotope ratio mass spectrometry

Abstract

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.

The effect of 18O‐labelled water vapour on the oxygen isotope ratio of water and assimilates in plants at high humidity

“…The retention time of the quercitol peak was c . 15 s earlier than the glucose peak and thus the baseline was generally separated; all other sugar peaks were likewise separated as in previous chromatograms of methylated leaf sugars (Lehmann et al ., ).…”

“…Moreover, the isotopic signal in assimilates derived from the mixture of xylem and atmospheric water sources in leaf water may be further altered after photosynthesis in downstream metabolic processes in different tissues, for example, via oxygen isotope exchange of carbohydrate carbonyl groups with leaf water, in hydrolysis reactions, and due to equilibrium and kinetic isotope effects in various enzymatic catalysed reactions (Schmidt et al ., ; Lehmann et al ., ). However, it remains poorly understood how the xylem–atmosphere mixture in leaf water is incorporated and partitioned into different assimilate pools at a compound‐specific level (Lehmann et al ., , ).…”

The 18O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

“…The measurement precision was typically <0.4‰ ( SD ) for oxygen and carbon isotopes. No significant oxygen isotope fractionation was observed during sugar purification (Lehmann et al, ; Lehmann, Gamarra, Kahmen, Siegwolf, & Saurer, ).…”

“…δ 18 O values of glucose and sucrose were analysed before and after the 9‐hr labelling event by gas chromatography (GC)/pyrolysis‐IRMS for 38 species of eight different growth forms. An aliquot of sugars per sample (~2 mg DW −1 ) was transferred to a 2 ml reaction vial, frozen, freeze dried, and then methylated (Lehmann et al, ; Lehmann et al, ). Methylated sugars were injected (splitless at 250°C) and separated on a 60 m, 0.25 mm, and 0.25 μm ZB‐SemiVolatiles GC column (Zebron, Phenomenex, Torrance, CA, USA) in a Trace GC Ultra gas chromatograph.…”

“…All samples were measured three times within a sample sequence. Interspersed sugar standard mixes of different concentrations were used for drift and amount corrections (Lehmann et al, ). The average measurement precision ( SD ) was 0.5‰ for glucose and 0.3‰ for sucrose.…”