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