Compound-specific stable carbon isotopic signature of carbohydrate pyrolysis products from C3 and C4 plants

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BACKGROUND: Pyrolysis-compound specific isotopic analysis (Py-CSIA: Py-GC-(FID)-C-IRMS) is a relatively novel technique that allows on-line quantification of stable isotope proportions in chromatographically separated products released by pyrolysis. Validation of the Py-CSIA technique is compulsory for molecular traceability in basic and applied research. In this work, commercial sucrose from C4 (sugarcane) and C3 (sugarbeet) photosystem plants and admixtures were studied using analytical pyrolysis (Py-GC/MS), bulk δ13C IRMS and δ13C Py-CSIA. RESULTS: Major pyrolysis compounds were furfural (F), furfural-5-hydroxymethyl (HMF) and levoglucosan (LV). Bulk and main pyrolysis compound δ13C (‰) values were dependent on plant origin: C3 (F, -24.65 ± 0.89; HMF, -22.07 ± 0.41‰ LV, -21.74 ± 0.17‰) and C4 (F, -14.35 ± 0.89‰ HMF, -11.22 ± 0.54‰ LV, -11.44 ± 1.26‰). Significant regressions were obtained for δ13C of bulk and pyrolysis compounds in C3 and C4 admixtures. Furfural (F) was found 13C depleted with respect to bulk and HMF and LV, indicating the incorporation of the light carbon atom in position 6 of carbohydrates in the furan ring after pyrolysis. CONCLUSION: This is the first detailed report on the δ13C signature of major pyrolytically generated carbohydrate-derived molecules. The information provided by Py-CSIA is valuable for identifying source marker compounds of use in food science/fraud detection or in environmental research. © 2015 Society of Chemical Industry © 2016 Society of Chemical Industry.
This work has been partly funded by the Spanish ‘Ministerio de Economía y Competitividad’ through project GEOFIRE (CGL2012-38655-C04-01). Dr J.M. de la Rosa is the recipient of a fellowship from the JAE-Doc subprogram financed by the CSIC and the European Social Fund.