Effect of 13C enrichment and sugar type on analysis of sugars by gas chromatography/combustion/isotope ratio mass spectrometry

RATIONALE The objective of this investigation was to test gas-chromatographic compound-specific analysis for studies on the isotopic composition of 13C-enriched sugar molecules. The effects of 13C enrichment and type of sugar (C5, C6) will provide valuable information on isotopic correction for future studies employing 13C-enriched sugars. METHODS Five sugar solutions of xylose, mannose and glucose with 13C enrichments ranging between 1.1 and 1.5 atom-% were prepared. The 13C enrichments of the initial sugars were measured by elemental analyser/isotope ratio mass spectrometry (EA/IRMS); 13C enrichments for derivatised sugars were obtained by gas chromatography/combustion/IRMS (GC/C/IRMS). RESULTS The linear relationships between the 13C enrichments of the initial sugars and the values for the derivatised sugars were sugar-type dependent. Corrections for GC/C/IRMS values took into account the kinetic isotope effect (KIE) of the derivatising agent associated with the coefficient (Kd) and a newly introduced second coefficient (Kc) associated with the KIE of the sugar. While Kd was constant, Kc varied with sugar type. During derivatisation acetate groups with 12C and sugars with more 13C reacted faster. CONCLUSIONS Coefficients for the specific ranges of 13C enrichments under study have to be assessed and the reactions of different sugar types have to be taken into account to avoid underestimation of 13C enrichment of up to 9% (C5) or overestimation of up to 4% (C6). Copyright (C) 2012 John Wiley & Sons, Ltd.